hybrid to mild phev conversion?
 

I'm sure people have done conversions of their nonplugin-hybrid to plugin without the extra battery expense. What were the results. On our C-MAX we come home with the battery at about 50% charged. What if there was a trickle charge circuit that could be added that would make sure the EV battery was topped off before taking it out again. Not looking for a quick charge so hopefully heat would not be an issue. I'm thinking that being able to start out every morning with a fully charged EV battery, thanks to the electric grid would be a reasonably good ROI.

I'd like that too, if just to balance the cells in my battery pack. Over time the load level between individual cells in the battery pack will start to differ; while some are almost empty others will be full. This will reduce the effective range of the battery pack and may damage the cells as they get underdepleted or overcharged.

A gentle overcharge may top off all cells while those that are already full will not get damaged. A trickle charge will not only give better initial performance, but better performance all round.
It's the not knowing how to that's holding me back for now.

Long story short, no.

Enginer made a phev kit for various hybrid cars and suvs. In my honda insight I managed a top of 103 mpg, about a 4 hour run time, 5 hour recharge time. Epa is 43.

Even though I got a later more advance kit, it paid for itself with supreme mpg, but it too died due to quality control issues.

As for precharging your own hybrid battery, it helps if you are in a mpg contest, but on a daily bases it will help your pack fail faster. Batteries lives are measures in cycles from being recharged and discharged and to what extend.

The reason your battery is low when you come home is likely so the car can use the extra fuel burned for cold start up to recharge it the next morning. Your cars computer likely only uses 60% or so of the whole capacity of the pack, so it can be cycles thousands of times in daily use.

As an Insight owner and like many other insight owners it seems the least you use of the IMA system the better your mpg is.

I have tried this with my Prius, a charge at a low rate (100mA) does not equallise the cells, it actually seems to make them more unequal...which supprised me, I think it is because the self discharge is so temperature dependant and the most full cells get warm and end up the lowest.

You are right, it does not work on the prius cells. It only works on the cylinder cells. The charge used is 350ma, which btw is what most wall warts use to charge nicad batteries. The non US models had a charger included in the trunkthat did something similar in a different way to revive a low or bad pack.

My plan was (you talked me out of it) to trickle charge it every once in a while.
I suspect my pack is not entirely fresh; strong support is always short and never full up the blue side of the charge dial; doodling in EV is only possible for a few hundred meters, no matter how careful. Never had an IMA failure yet though, no positive/negative recalls or what.

RD, you are in Europe, I was of the understanding you guys had ready available adjustible power supplies and it was just a matter of hooking one up, setting it to 134 volts no load and 350 ma output and wait 36 hours. :eek:

Its likely your 12 volt battery that is so-so. I bet if you switched it out you see a vast improvement in your IMA behavior. :thumbup:

Yup, they grow on APS trees over here but we're out of season right now ;)
Well they might sell some over here, just don't know. My brother-in-law is the expert on stuff like that, but I'm a bit wary since he all but disected me over my WAI, LGB and block heater experiments. Better know what I'm asking before I do.

You made me realize that while I (like you) told others to test the voltage of their 12V battery, I didn't follow that advice myself :o even though I did on previous cars and all the bikes I had. Will do so tomorrow.

One map light left on accidentally ran my battery flat in just 10 hours or so. I did not expect that to happen as my car was barely 1 year old :confused:.
It won't happen again as the map lights are now LEDs. I rely on my ability to make the same mistake twice :).

Yeah, online it seems those over seas have one laying around inaddition to a scope to look at waves. Maybe one day I can go over seas and see how life is really like and what quarks exist inr elation to the US.

I had a 10 farad cap with voltage read out and subwoofer with amp attached to my Insight. Its connected to a remote wire and i turned the key on one day without starting it and saw the voltage tne next morning was 11.7 volts. I had connected the battery charger to my car other night and thought i had fixed it. It was warm again for a few days, then BOOM, 20 degrees out F. I had to use my key to unlock the door, then 5 seconds later the alarm went off and it wouldnt start. I checked the cables again, nope, had to jump it. Previously I lucked out and fixed it by readjusting the battery cables.

I have 3 of the NHW10's imported from Japan, they have "D" cells. I have been working on the batteries, replacing cells etc as they were not supported by Toyota here. (New Zealand). recently, toyota have started supporting them and I have bought a new pack for one of them from Toyota. The small 12V charger you talk about only charges the pack to enable the car to start if it is left standing for a long time. The "D" cells do act very differently to the prismatic ones, if you charge a totally flat D cell carefully it recovers full performance, but the D cells don't. the D cells in these are 16 years old and have done 300,000 km or 200,000 miles, the self discharge rates have increased on some cells to the point where if they stand for a week they are flat.

One other thing to consider is the magnitude of the possible benefit ... in addition to the possible issue raised of more cycles per year generally means fewer years of useful battery life.

You can calculate the maximum possible benefit if you know the general system efficiency and the battery size ... just compare the energy contents.

For example ... a Gen-1 Honda Insight OEM Battery has at most ~6.5Ah , 144 V Nominal = 936 wh max from 100% to 0% DoD window ... that generation IMA system is around ~90% efficient ... so maximum possible would be ~842Wh of plug in energy to the wheel ... Although in practice it would be much lower than this , because you don't get the full 100% window , and peukert effects , etc ... in practice about ~470 wh to the wheel is more likely ... but even at the max upper end ideal ( a bit unrealistically optimistic case ) ... at roughly ~36 kwh of chemical energy per gallon and roughly 35% efficient ICE that ~842 Wh would only offset / replace at most about ~0.06 Gallons per such full 100% cycle charge... or from the ~470Wh more realistic case ~0.03 Gallons offset per such full cycle... it's something ... but is it enough to justify doing it... that's up to the individual.

I'm not sure I buy Cobb's assertion that topping off the batteries every night would reduce the life of the batteries.
a) Owner's of cmax energi's does this now, as does any other plugin EV or PHEV
b) The charge/discharge cycle during normal driving is several times a day as the battery runs down and then is recharged either by ICE or by regenerative braking.
c) Slow charging up the battery overnight so that you start with a fully charged battery in the morning would directly allow the engine to primarily be used to move the car forward and not recharge the batteries when you might need extra power to get going.
d) The slow charge using 120V plug would probably be gentler (less heat) on the batteries then fast charging with the ICE.
e) It seems to me that topping off the Etank overnight would reduce the number of charge/discharge cycles.

Go for it. I am just repeating what Ive read on the insightcentral form where a lot of smart people learn from their mistakes.

BTW, we have a few vendors that sells, rebuilds and replaces hybrid batteries too. :D

The latest information I have says that for li-ion battery packs you want to keep them charged between the range of 20-80% to maximize battery life.
Design News - News - Can EV Batteries Last 20 Years?
So a way to arrive home with about 20% left and a slow charge (slow also extends life) to 80% seems to me to be ideal. That would be about 60% of 1.4kWh or 840watt hours. A 200W charger I think wouldn't be that expensive.
Now there already is a couple of charging electronics designed in every c-max. The braking regenerative recharge system and the ICE driven charger. (At this time I'm not sure if they are actually the same). But if we could use those circuits that must already be conditioning the power to charge the battery then the 120V charger might not be that expensive. Anyone know where an electrical diagram of the CMAX could be downloaded?

This flies opposite to the experience of Insight G1 owners who have marginal packs, the trouble I forsee is that the various types of cells will behave differently and have different charge requirements, where my 13 year old pack likely enjoys a charge to be functional, perhaps a new pack should only be charged partway?

To balance the cells in an Insight G1 pack may need to charge at a very slow rate for up to a little over a full day, so perhaps we aren't all talking the same language.

Cheers
Ryan

Great subject and from what Ive read I am convinced no one really knows the correct answer, however there are plenty of examples that damage and shorten pack life.

Ok, first off we need to communicate if we are talking about % of charge of the pack itself or what the car uses which is typically less like 80%.

For example in the gen 2 insight I see 3 voltages, the car considered 112 to be 90% to full at times, 117 is FULL according to the SOC meter 121 is considered full and balanced hot off the charger.

I am guessing you are saying precharge the pack in this example to 112-117 volts or somewhere in the middle like 115 volts? Yeah, I can see that being some benefit and likely ok as long as its monitored. You could stack a few meanwell power supplies and fully charge the insight pack in 3-5 hours depending on its current soc.

Now if the car has lifepo4 or some form of lithium cells those go up fast in voltage when a cell is fully charged vs the rest, so if you are charging the pack you need to make sure it has some type of active bms and that system is fully operational if you are going to tap a few electrodes and back feed power to it like the Honda and prius guys do.

IamIan's comment prompted me to calculate the benefit in another way. Based on charging the battery with a max of 840Wh everynight and using a DoE rating of 220-265wH per mile this would mean about a max of 3 miles of additional electrical range per day. Depending on your daily driving habits this could be a lot or could be a little. Is it worthwhile? Good question, both in terms of the financial investment, and time to plug it in everynight to get 3 additional miles without needing to burn gas from the tank. I think the answer is different for each owner.

3 miles over a long trip may take care of all of your acceleration events, which is where your fuel economy drops into the basement.

So I would argue charging the pack (safely) for whatever paticular chemestry and type is in there is likely of benefit.

The pack is MADE to charge and discharge, to say you can't charge a pack due to wear, that the car repeatedly charges and discharges everyday is false.

Incorrectly charging the pack or taking it outside the best life charge level is another matter altogether.

Trickle charging as done on a G1 insight with a failed pack is altogether different than how you would approach the matter on a new car with a good pack.

Cheers
Ryan

Its just a shame all of our "hybrid phev experts" do not actually own or drive a hybrid nor have a phev kit installed. :eek::eek:

If you ever get a chance to drive one you will see you actually get more mpg without using any of the hybrid systems. Thats right. :eek:

Cobb,
I don't believe anyone disagrees with the assertion of getting better mpg. What is being discussed is the potential costs: battery lifetime (better or worse), costs of installing a charging kit. Some estimated it to be upwards of $900 just for charging. Time to plug the car in every night when returning home. Can you get each person that's driving the vehicle to commit? Is there a potential to void the warranty?
cheers

I own and drive a hybrid and an ev, no PHEV but that may come some day.

As for the 2nd statement that isn't entirely accurate, the prius warp stealth and P&G techniques are VERY difficult to pull off in a non hybrid. My cobalt P&G is not as effective as I would like for a varienty of reasons and the motor gets bogged down (flooded) when its cold out if I pulse and glide.

My insight can get better without the hybrid under specific conditions but also ends up with other issues without the hybrid on.

I own and use .. a HEV ... which I can and have run in a PHEV mode ... and I have and use a small BEV.on occasion as well ... not sure who you were referring to though.

The second claim is conditionally correct or incorrect... meaning ... weather or not the hybrid system is a + or a - to mpg will depend on the condition / context ... it is incorrect to claim it would be + in all contexts , and it is just as incorrect to claim it would be - in all contexts... which may not be popular ... but that is more accurate.

The hybrid system is useful for situations where it can help avoid using the brakes or run the ICE at a very inefficient load level. It also helps acceleration, of course.

In situations where you can keep a constant load by varying the speed, like when negotiating a small hill on the highway, that is preferrable to drawing from the battery on the ascent and filling it back up descending, as the losses in the movement->electricity->battery->electricity->movement conversion are substantial.

Nowadays I try to coast on level load, e.g. not drawing and not storing.
When driving slow the electric mode will kick in by itself. I then go P&G varying the speed (if not hindering traffic) rather than maintaining speed drawing power. If I do the latter at some point the ICE will kick in and recharge the battery, but the FE while it does that is worse than when gently accelerating in the P phase.

It is great to have the hybrid system when you can put it to good use, but it is even better to avoid using it if that is possible too.

Inaccurately over simplified for my tastes ... but that might just be me , and my personal preferences.

It depends on context ... it is not always a + to avoid using it ... just like it is not always a - to avoid using it ... it's not that simple.

- - - - - - -

Just by fluctuating your speed any amount at all ... you ALWAYS increase the total joules of energy needed for wind resistance , compared to maintaining the same average speed as a steady speed ... that is just the reality of wind resistance.

Fluctuating vehicle speed is only a net + ... for the same average speed ... when the average ICE efficiency goes up by more than the increase in joules needed to fight wind resistance.

- - - - - -

All those conversion have losses yes ... but those losses are not always more than other losses ... sometimes for some conditions the round trip would be more losses ... and for other conditions the round trip is less losses.

There can be just as substantial and even more substantial losses from ICE efficiency fluctuations ... or from travel joules fluctuations ... etc.

- - - - - - -

And once it goes into the PHEV category of HEVs the effect of round trip losses are drastically reduced ... if not removed.

And for many people ... every 1 kwh of mechanical energy it costs in $ more than 3x as much to buy it from gasoline as it does from grid electricity, which pays for a lot of other losses.

Always nice to get a compliment.

If I fluctuate my speed downwards, topping that hill, wind resistance might even be lower rather than higher. Wind picks up at height. But even if it gets higher, that's probably preferable to the 50% or so you lose in the charge-to-discharge conversion.

When the speed variation is low, the amount you lose on the bit you go faster is hardly any bigger than the amount you gain while goiing slower. The relation between wind resistance and speed is quadratic; so it rises sharply by raising the speed but also drops almost as sharply by lowering it. It pretty much equals out.
The hybrid conversion does not equal out; that is about 50% loss for any amount you use.

It is impossible to attain perfection on such a complex matter as this in just a few sentences. But that does not mean that you cannot draw general conclusions.

Cobb's statement was more to the point than many like.
The "Hybrid is good, must use it always" rule simply does not work. The system is great to have when you need it, but you get better mileage and longer battery life by minimising its use when you don't.
And it shows; I just got my best ever FE on my 36 km commute: 3.4 l/100 km (69 mpg) as indicated by the MID; cold start, ambient 20 degrees Celsius, mild side wind, mainly doing 55 mph.

I will agree that the correct speed to use for wind resistance is the air to vehicle speed and not the vehicle to ground speed ... so sure.

I will agree to that exception ... if you are able to accurately predict the wind speed changes correctly in real time before they happen ... then sure ... it would be possible to combine vehicle speed fluctuations with that precognitive ability in order to not have a net of more aerodynamic loss joules.

The round trip can loose 50% ... or in other conditions it looses only 25% ... or maybe in yet other conditions as little as ~13%... it depends.

It is not the HEV that is % wasteful with joules of braking , compared to the non-HEV.

The ICE can also change that much or more in it's operating efficiency.

And there is also the other potential losses from other sources ... including the air to vehicle speed fluctuations... route choices ... etc.

It is not HEV% loss vs 0% loss ... the non-HEV option can have losses too.

If the choice in a specific condition is 43% loss or 42% loss ... the 42% loss is better ... it is better if it is the HEV round trip ... or it is also equally better if it is the avoid using the HEV option.

(Bold added)
No ... it does not.

The smaller the fluctuation the less of a penalty ... but there is always a aerodynamic joule penalty for the air to vehicle speed fluctuation.

We can crunch the equations if you like ... but ... it does not balance out.

Agreed.

I disagree with the "must always use it" people ... just as much as I disagree with the "can do better without ever using it" people.

Just telling people to avoid it ... avoid it... and avoid it some more ... is ultimately less useful and helpful than explaining the + and - ... of when using it is + to MPG ... and when using it is a - to MPG.

I agree that both hybrids the Honda and Prius has some other efficient designs and features about them that leads to better mpg regardless of the drivetrain.

I am guessing the net lost in mpg using them comes from not being able to have your cake and eating it. Maybe the guy who was hit on the head with an apple is to blame? :eek:

We more or less agree on a lot of stuff, finaly ;)
With 'pretty much' I meant 'almost'. But yeah, lets crunch numbers.

Air resistance has a quadratic correlation with speed. Higher speed also means longer distance travelled so we can represent it as a function of speed: R = C * V * V (where R is resistance, V the speed and C a constant representing the aerodynamic efficiency).
The energy required to overcome the resistance is the product of that resistance and the distance traveled; the distance is linear to the speed.
The equasion for the energy would be the same, just multiply both sides with the speed; ergo R * V = C * V^3 (^ designates power)

So now we compare that to a situation where the speed is slightly higher half of the time and the same amount lower for the other half. Let's call the difference D.
The required energy over that would be R * V = C * ((V + D)^3 / 2 + C * (V - D) ^3 / 2)
Simplifying the equasion it becomes R = C * (V^2 + 3D^2).
So the increase is just 3D^2

In words the total resistance increases by 3 times the square of the difference.

If the speed variance is say 10% of the average speed (like doing 60 mph and 50 mph alternatingly instead of a constant 55 mph) the increase in resistance is 3 times the square of 10%, which is just 3% for a 10 mph difference between high and low speed.
That's not nothing, but it is much less than you'd expect. It seems to contradict common sense. But the math adds up.

We can check the formula by making D equal to V. Doing half of the time double speed and half of the time at a standstill should see 4 times the power needed as the resistance while moving is 4 times higher, and all of the distance was covered at high speed. And sure enough the formula yields a 300% increase, so a total of 4 times higher.

Do the formula on a small variance (like 2% for +/- 1 mph at 50) then the formula yields just an 0.12 % energy increase. That's less than a mile on a full tank even if the only force in play is air resistance.

So there you have it. Yes, varying the speed does increase the total amount of energy you need to overcome air resistance, but the increment has a quadratic relation to the variance so if that is kept within a reasonable range, the extra energy required is not a major factor.

Today it was cold: just 8 Celsius coming home vs. 25 yesterday and it hurt FE. But I did get to practice P&G technique on a country road (being held up by some slow movers), alternating gentle acceleration to 40 mph while keeping the revs at minimum with coasting 'zero load' style to 30.
As I have a l/100 km indication on the MID it is not very accurate, but it had 4.0 l/100 km @30 km in the trip when I started P&G and 3.8 @35 km when I got home.
The fuel consumption on that stretch was 2.6 l/100 km (give or take half a l/100km). I did not draw from nor add to the battery doing that.

Give me lots of time and an empty road and I can easily get my Insight over 80 mpg by P&Ging like this :turtle:. Make it a windless 30C day, then maybe 100 mpg is attainable.

:thumbup:

fair enough ... as long as you recognize the penalty... your ahead of many P&G advocates who refuse to do so.

yup a 3% penalty.

If one is able to improve the average ICE efficiency by more than the P&G varying seed penalty is there a net benefit... if not it is just a penalty.

I have seen many P&G die hard advocates do much much more than 10% from high speed to low speed.

Driving at slower average speeds consumes less energy P&G or not.

The better comparison is the same average speed.

And as it so happens ... another forum member did some constant speed tests with a Gen-1 Insight on flat level ground ... so you can compare your P&G MPG at the same average speed to his ... and see where the P&G is giving you a benefit , or not.

So @ and average trip speed of 30 MPH you have to do ... much better than 80 mpg ... you have to get better than 131 MPG... or keep the ~80mpg but do it at an average speed of over 60 MPH ... if you get less than that at the same average speed ... then that's the breaks .

http://forkenswift.com/album/24-grap...pg-insight.jpg

The G2 does not get that good consumption on really low speeds. I feel best speed is about 85 km/h (52 mph). I can get below 3 l/100 km on a constant speed doing that in the right conditions. At 60 km/h the revs get down to 1200 RPM and it seems to suffer slightly. Any slower and the revs still stay at 1100-1200 RPM, so from there the loss increases substantially unless it switches to EV mode. (but that... you know)

So, P&Ging does help me overcome the Insights inefficiency at the low revs&low load combination. I have to stress that I drive tha same route regularly, but never managed to improve the MID's FE by .1 on constant speed, let alone the .2 I managed this afternoon. So I was pretty convinced about P&G.

P&G at highway speeds is useless in the G2. It does fairly well on constant load. I may enjoy a short glide on the down slope from a bridge (so many canals here, the highway jumps up and down every 2 miles or so)

I do use the hybrid system to 'customize' my glides as to match up with traffic and such.

And I did a funny experiment. On the last stretch in the woonerf I tried to prevent EV by just giving it enough boot, until it jumped to EV mode regardless as it sensed the battery was full. That made for some economic driving as the FE while avoiding EV mode was still good, while if you first drain the battery the FE when the ICE finally kicks in is not.

Just as P&G can help and be a + ... when it is able to increase the average efficiency of the ICE more so than the non-P&G average ICE efficiency would have been at the same average speed ... with a bit more additional ICE efficiency gains needed to over come the aerodynamic penalties for the speed fluctuation of the P&G.

Principles are the same ... fast , slow , or any speed.

% variation causes the same % of aerodynamic penalty at any driving speeds.

The increased difficulty many P&G users run into at faster speeds ... is how much more ICE efficiency can be gained at higher average speeds and higher average loads ... there are limits ... the ICE has a best case max efficiency.

If the ICE steady state is already operating at peak ICE efficiency ... the only way to improve MPG is by improving the ratio of ICE efficiency and energy consumption ... ie reduce the consumption more than you reduce the ICE efficiency... some of that can be smarter driving ... or just driving at a slower average speed.

You can't see a net MPG gain , if the P&G extra aerodynamic penalty is equal or larger than any remaining possible gain in ICE average efficiency for the same average speed.

Just like P&G there are + and - aspects with the HEV system.

It is not a + all the time used in any method ... neither is P&G.

The right tool for the right task.

The limits on the G2's efficiency at low speed are both physical and functional. The RPM is lower at the same tpeed than with the G1, and the CVT will keep the revs at 1100 no matter how slow you go. When that happens the FE drops linear with the speed. Unless you can P&G.

At low speed air resistance is way less than at high speed, and so is the penalty for changing speed.
So I see no problem in my P&Ging at low speed. I get good mileage, even though the last 4 months were colder than average for the time of year. P&G plays just a minor role in that, but if you look at my record you will clearly see the point where I learned to reduce the use of the hybrid system.

It is great to use the EV mode when the battery is full, so if you can charge it by the mains or charge on coast where you'd need to brake otherwise, that is the best you can do. As you said, it will always depend on circumstances.
Trying to keep the battery full will make the system use it whenever it can, while if you draw it empty it will try to replenish it given half the chance.
If you want to stay in control you need to anticipate the chances you will get to draw or load; e.g. draw it empty before going down that mountain and keep it brimmed before going up.

It is the change in ICE efficiency ( weather or not RPM changes at all ) that has the ability to give a net +MPG even with the penalty P&G always gives to energy cost at the same average speed.

The Penalty is still there ... always there ... the principles are still the same at any speed ... the act of P&G has to result in some other part of the system ( like the ICE ) improving more than the act of P&G itself gives you that penalty... there has to be a bigger + somewhere than the P&G gives a - , in order for it to be a net +.

Neither do I ... I never meant to indicate that I did.

Nor do I see a problem with anyone P&Ging ... it's their drive they can drive it anyway they like ... and if their goal is to travel the same distance at the same average speed while consuming less gallons to do it ... sometimes P&G will help them ... other times it will hurt them.

I think it is ultimately better for them to understand how and why it helps and how and why it hurts ... that way they are more able to make the best choice for a given set of conditions.

That is the kind of over generalized one sided suggestion I disagree with.
For multiple reasons ... as touched on previously.

Yes that part I agree with ... it is a known and tested fact.

It is how I myself prefer to tell people about HEV system use and P&G use.

... with some extra batteries?
 

I am considering to turn my Insight into a mild PHEV by adding some 1 kWh op LiFe(Y)PO4 (Lithium Iron Phosphate or LFP) batteries and stuff. Charge that at home, gently (all but) deplete on the move, to aid acceleration and to allow for P&(e)G-ing on the highway. Every time I can put 1 kWh into my commute it should save me at least half a liter of fuel, so it has the potential to save me over € 200 each year just on commutes.

The idea is to feed the IMA system with 500-1000 W continuously once power is engaged, maybe making it voltage-dependent to feed more into it when the system needs it and maybe even charge back a bit under braking.

Maybe could add some thin foil solar cells on the roof later, if the setup works fine.

The batteries have to be LiFePO4 or LiFeYPO4 type as those seem ideal for this kind of use. But I haven't looked into how to feed the IMA yet. Any tips?

Maybe I can compensate for some of the extra weight by exchanging the under hood lead acid battery for a smaller LiFePO4 battery.
Then it shoud not have a BMS system as that interferes with the high current draw while starting, but I wonder if I can safely do so. If the battery gets charged at over 14.4 V (3.6V per cell), then I guess not.
If it (the lead acid battery) gets charged at less than 12.8 v then the LFP wouldn't get charged at all.

Of course I could use a small BMSed LPF battery and a string of supercaps to circumvent these issues. But I just wanted to keep it simple.

So... what would be my chances to make this successful?
Should I create a low-amp high-voltage pack slightly over the IMA's operating voltage and just bleed it in?
Or should I use a DC-DC converter, controller and stuff?
Or is this all just a bad idea?

Sense I've known people who have done this kind of thing ... one form or another ... I'd say it's just a question of if the amount of personal investment ... time and such ... is worth it to you ... I have zero doubt about weather you have the ability to make it happen.

All of those and others are all options ... all with their pros and cons , for you to weigh out and make a personal choice on.

Grid Charging the OEM NiMH is fairly limited ... but people do , do it... and it is the least complex ... least expensive ... and easiest.

Grid charging 2 or more OEM NiMH packs in parallel ... gives more capacity... still fairly easy , and fairly low cost.

Using a dedicated booster battery to 'bleed' in replacement current ... can be done with either the DC-DC from a lower Voltage booster pack ... or with some other current limiting controller from a higher voltage pack... it does add in the complexity and conversion efficiency hits for the electronics ... but if done well ... those can be very very small hits... this is the 3rd level of more complexity and cost ... but also tends to be the 3rd level of PHEV potential gains.

Some people just upgrade / replace the OEM IMA NiMH with a more modern ... more energy dense battery pack ... it means fooling the OEM BCM , and having your own BMS , and Charging system ... but it does allow for the most kwh per kg of HEV battery in the car ... for example ... the Swap people do in the Gen-1 Insight to A123 20Ah pouch cells gives about 3 to 4 times more energy than the Old OEM NiMH ... without adding any weight to the car... this tends to be the most complicated and most expensive ... although it has been done / proven.

No matter what ... have fun with it.

Thanks. Swapping the NiMH pack for LFP's (like the A123 cells) would indeed be best FE wise, but I still got warranty on my good NiMH pack.
I suspected it to be lazy by infrequent use in its first year, but it did really surprise me going up and down the mountains in Germany; the meter stayed fat in the blue zone for minutes on end going uphill. The MID showed a fuel usage of less than 8 l/100km for that stretch, while my ears popped. :)

My aim now is for the long string of batteries to hook into the pack on contact.
I will look into that charge/discharge limiter to prevent the individual BMSes from kicking in.

Best of luck ... just a few notes , you probably are already aware of.

Plan for the system to handle peak possible inrush current / power rates ... Although the packs change as they age , temperature, SoC/SoE , etc ... if you design for the end points of max and min , you will be best set.

AFAIK , the minimum net resistance for the whole OEM IMA NiMH pack all cells and connections is ~360mOhms ... V=IR ... the minimum OEM IMA NiMH pack voltage is ~120V ... the Max is ~187V.

So you can use those and the min max specs on the booster battery you are planning to connect , to get a reasonable prediction of the direction of peak current / power flow ... and the magnitude.

Then you will be in a good position to be able to either plan for / design the charge/discharge limiter you mention ... and/or ... chose when in what situations to use it.

Best of luck.:thumbup:

Thanks. I believe those numbers are for the gen1 pack though, the gen2 has a lower voltage pack.
And I will regulate max current both ways, And put an amps meter on that I can read behind the wheel.
I't like to keep the voltage somewhere within the operating range, so that it recharges under braking. This way it will lower the hysteresis loss e.g. raise the charge/draw efficiency. But it need be on the high side or it would stay full and not be able to take much grid or solar charging.