Alternator bypass & engine preheater mod

[brucepick]

Paul,

I owe you a small clarification on the battery project.

The 40 AH LiFePO4 was capable of powering the car (minus headlights) for 3 hours, with minor occasional use of fan or wipers. Nominally rated 12.8V. With an allowable 80% drawdown of battery capacity and a derived approx 10A load due to running the basics (computer & fuel pump), the 3 hour life is about right.

The ~100 AH lead acid, nominally 12V of course, was effective for headlights for only about an hour. This was mostly because 12V isn't really enough for headlights, they need about 13.5-14.5V, subject to user preference and opinion. Of course voltage dropped below 12V pretty quickly. At night the illumination from slightly reduced voltage just wasn't ideal.

The other limiting factor for the lead acid pack was that I wanted to drain it down only about 50%, to preserve its longevity. Lithium, on the other hand, can safely be drained to about 20% of it's rated capacity.

Thus my interest now in several booster converters in parallel, to power the headlights and probably also brake lights and fan.

I'm certain I could have powered the stereo off the lead acid for many hours; it doesn't need ~14V to satisfy my entertainment needs. However performance stereo buffs have been known to use multiple 14V batteries in parallel for earth-shaking bass.

[paulgato]

Originally Posted by brucepick

Paul,

I owe you a small clarification on the battery project.

The 40 AH LiFePO4 was capable of powering the car (minus headlights) for 3 hours, with minor occasional use of fan or wipers. Nominally rated 12.8V. With an allowable 80% drawdown of battery capacity and a derived approx 10A load due to running the basics (computer & fuel pump), the 3 hour life is about right.

Sounds about right. These LiFePO4 batteries seem much better than Lead Acid in every way really. Just expensive.

The ~100 AH lead acid, nominally 12V of course, was effective for headlights for only about an hour. This was mostly because 12V isn't really enough for headlights, they need about 13.5-14.5V, subject to user preference and opinion. Of course voltage dropped below 12V pretty quickly. At night the illumination from slightly reduced voltage just wasn't ideal.

I realised I was wrong in an earlier post. I am not using those (44w) Phillips EcoVision headlight bulbs at the moment after all. I found they were a little too dim at low voltage. I was intending to up the voltage a bit with the headlight relays and heavier cable and then re-fit the EcoVisions to save a bit of power, but haven't yet got around to it.

I had forgotten that I had ('temporarily' - ha ha) fitted Osram Nightbreaker bulbs, and those do seem to work well at low voltage. They are sold as being whiter and brighter than normal, although they only use the standard 55w of power, so remain legal and won't overload any circuits. The 'net wisdom' on the Osram Nightbreakers is that they do work well but tend to burn out in less than a year, so work out expensive. I find that they work well for me at 12.5 volts and are acceptable in brighteness and colour at any voltage at which the battery is still above 50% charge. (In fact they are acceptable in brightness even if I have discharged the battery to the point where the engine will not start - as I found out the other night! I had a spare battery with me so I was OK.)

I think my comments about the headlights being alarmingly dim at 11v must have been based on either standard bulbs or the Phillips Ecovisions because on this last trip (150 mile round trip, half in darkness) I didn't once feel the need to stop and reconnect the alternator because the headlights were getting dim, even though the voltage had dropped way below 11v, whereas I know I've been compelled to reconnect the alternator due to dimming headlights once or twice this last Autumn.

I guess the Osram Nightbreakers (and similar bulbs) have been designed to maximise light output at the cost of a shorter life. Run at 12.5v they seem to shine pretty much like a normal bulb would at 14.5v, and at 12.5v they will probably last as long as a normal bulb too. I think that since I am almost not using the alternator at all now (so my mpg is no longer directly affected by current draw) I shall stick with the 55w Osram Nightbreaker bulbs, as they do seem to work well at lower voltage.

The other limiting factor for the lead acid pack was that I wanted to drain it down only about 50%, to preserve its longevity. Lithium, on the other hand, can safely be drained to about 20% of it's rated capacity.

LiFePO4 batteries seem way better than lead acid. A 50Ahr lithium battery has the same useful capacity as a 90Ahr lead acid, will last many times longer and probably weighs less than a third of its lead acid aquivalent.

Thus my interest now in several booster converters in parallel, to power the headlights and probably also brake lights and fan.

You might want to try the Osram Nightbreakers, or similar brightness-boosted bulbs. It may be all that's required, and would save a lot of hassle if it works.

As for the brake lights, I can heartily recommend swapping the incandescent bulbs for red LED bulbs. LED's are not voltage sensitive in the way that filament bulbs are. The LED's I fitted use 1/5 the power, are much brighter and 'redder' (the red light filling the lens evenly rather than being brighter and paler in the centre) and they switch on instantly, so giving drivers behind an extra 1/3 second for braking. They also have an expected life longer than the expected life of the vehicle, so hopefully I'll never have a brake light fail on me again.

I'm certain I could have powered the stereo off the lead acid for many hours; it doesn't need ~14V to satisfy my entertainment needs. However performance stereo buffs have been known to use multiple 14V batteries in parallel for earth-shaking bass.

14v batteries are available, if expensive, and alternators can easily be 'tricked' with a couple of diodes into producing a higher voltage to charge them, but 14v mains chargers are not so easily available.

[paulgato]

The 90Ahr AGM battery in the engine bay is being charged via the bumper socket on my driveway every night and that provides adequate electrical power for my daily driving needs.

In a way, that is probably the optimum level of work, cost and trouble I should go to if cost-saving is my goal. However, my goal is to maximise mpg, so I shall make my life complicated and go the extra mile to fit a 2nd battery, 2nd mains charger, a DC/DC converter and a whole lot of extra wiring. My main reason for being so unreasonable is to extend my alternator-free driving range to about 300 miles, which I'm unlikely to exceed very often in any one day. So that's my main reason - to get as many miles per gallon as possible on every occasion. But this 2-battery setup will also probably extend the life of the batteries considerably, as on most days I will only be discharging each battery by 20% or so.

My general advice to anyone more sensible than myself, would be to get the biggest AGM battery you can fit in your engine bay and charge it every night from the mains via a good quality charger also mounted in the engine bay. That's relatively simple and should save money as well as a considerable amount of fuel. The savings you make on daily commutes are far more significant than savings on occasional longer journies. For longer trips, just use the alternator.

That said, I'm going to fit a 2nd battery.

I had just bought a DC/DC converter for this purpose when a friend asked me why I didn't simply add a 2nd battery in parallel with the first one. I did a little reading around that and found that basically he has a point. Wiring two batteries up in a simple parallel arrangement would work well, but there are potential pitfalls compared to running the 2nd battery via a DC/DC converter. The main thing is that unless the 2nd battery is right next to the 1st battery then you need seriously fat cables to connect them together. Also, you need to connect both +ve and -ve terminals together with these 'fat as your finger' cables, and ground only the rear-mounted battery, to avoid current imbalances. (And those cables would also have to be fused at either end with say 300A fuses because any short on the cable length would otherwise be disasterous, with exploding batteries, fire, total loss of the vehicle or personal injury being distinct possibilities.) The two batteries should also be of the same type, same manufacturer, same Ahr rating and same manufacture date to avoid problems. Those cables and fuses would cost close to £200, and would not be easy to route through the vehicle. You'd have to be super-careful to avoid any chance of abrasion. (The 300A fuses will stop the batteries exploding but may not blow in time to prevent a fire in the event of a short to ground.) So not straightforward, but if I were starting from scratch I might well do it that way for the sake of simplicity and efficiency. Since I don't have room in the engine bay for two large batteries, I might consider mounting both batteries in the rear so they are both being charged and discharged at the same temperature. Or just use one enormous battery in the rear.

However, I have got half-way along the path of connecting a 2nd battery via a DC/DC converter, and that approach does have advantages (like not needing monster cables anywhere) so I shall go ahead and complete the set-up. I got a DC/DC converter a week ago...

E914 12A 12v-12v Battery Charger (12V Turn On)

...and I'm currently collecting together all the bits and pieces to wire it up. The unit will put out a constant 12A at 14.0v. It has a built-in donor battery voltage cut-off of 12.0v, to protect the donor battery from becoming discharged too deeply, and I think that is probably about right for my purposes, as 12.0v at 12A load probably corresponds to about 12.2v resting voltage, which corresponds to about 50% state of charge. It has a low current 'control wire' which I will wire up to a manual switch for now but which I plan eventually to wire up to the ignition switch (or perhaps to the in-tank fuel pump which only runs when the engine is running) so the unit will switch on and off automatically. I will then have a three-position switch somewhere on or near the dash so I can switch the DC/DC converter ON, or OFF or to AUTO. (It would be good to be able to overide the donor battery cut-off voltage threshold, so I can use the 2nd battery in an emergency to charge the starter battery even if the donor battery is also 50% discharged, but I'm not sure how to do that just now.)

I'm going to set the system up temporarily in the passenger footwell with a spare (non-AGM but otherwise sound) car battery. If that seems to work OK I shall buy another AGM battery of around 110Ahr, mount it securely in the spare wheel well, and route all the cables through properly from the engine bay. The 2nd mains charger will also go in the rear of the vehicle, as will the DC/DC converter.

[paulgato]

I just received a 100Ah Yuasa YPC-100-12 cyclic AGM battery. (30kg. Ouch!) That will go in the spare wheel well soon, although I'll test it out in the passenger foot well to start with, so I can monitor voltage/current, etc. easily. It cost £138 and should last at least two years of daily use and probably more. It should pay for itself in fuel savings.

I've been using the DC/DC converter/charger with a spare non-AGM car battery for a little while, and the system does work well. The converter provides a steady 12A at precisely 14.0v into the (90AH AGM) starter battery and maintains the starter battery system at between 13v and 14v, depending on load.

On dry days the 'donor' battery supplies all the power needed by the car (approx 9A) until its voltage drops below the DC/DC converter's battery protection threshold of about 12.0v, at which point it modulates the current gradually down while maintaining the donor battery's voltage at no lower than 11.8v.

On wet or dark drives, with higher electrical load, I reckon the two batteries share the load roughly 50/50, and if it's both wet and dark the starter battery provides more than the donor battery does, although when I park up I can leave the donor battery to re-charge the starter battery through the converter. My hope is that adding the second battery and DC/DC converter will bring both batteries back within their 'comfort zones' so they'll both last much longer. With just the one battery I was often using a full 50% of the battery's capacity on routine daily drives, and that puts a bit too much strain on the battery. With two batteries, the typical daily discharge of each battery should be between 15% and 25%, which puts far less strain on them, whilst more than doubling my maximum alternator-free driving range on the occasions when I need it. The extra weight is an issue, but I think it's worth it.

The converter runs cool (and therefore efficient) until it begins to modulate the current, at which time it does get quite warm for a short while until the current drops below 5A, and then it becomes cool again. I plan to add a separate adjustable voltage-sensitive switch to cut the converter out at a donor battery voltage of about 12.2v. That will limit daily DOD to about 50%, and will keep the converter in its cool and efficient non-modulating mode. I'll still be able to overide that 12.2v limit manually if I need the maximum range on a long drive or if I ever need to recharge a flat starter battery.

Today I started taking the glove box, etc. out so I can run cables through the firewall from engine bay to spare wheel well. One big advantage of using the DC/DC converter rather than simply connecting two batteries in parallel is that I only need to run normal 12-14 guage cable or so. No scary monster cable required, nor any scary 300A multiple fuses and isolators. I'm protecting things with standard inline blade fuse holders and 15A fuses. In fact I'm using the existing (30A fused) wiring to the rear 12v power outlet socket, and that seems fine and everything feels very safe. I just need to run the charger cable through to the rear really, but at the same time I will lay in a low amps multi-core cable for various control and monitoring puposes.

Just one other thought is that it would be really cool to add a couple of small solar panels to the system - perhaps one 20w panel for each battery, perhaps mounted inside the two rear side windows in the load area. More watts would be better but more watts would have to go on teh outside of the car, whcih compicates things, and even 40w should extend range and generally support the batteries to a useful extent.

I have to say this project is taking up a lot of time and I'm looking forward to getting it kind of complete and all hidden away in the spare wheel well where it belongs. I'm getting a solid 10% mpg improvement from it, so definitely worthwhile, but I'll be glad when it's all complete, all running automatically, and I can move on to the next mpg mod on my list.

[paulgato]

I think I destroyed my alternator today.

I was trying to see if it was possible to stop the alternator putting out power by 'softly grounding the field wire' through a light bulb to de-energise the field winding. This is so I could finally install an alternator ON/OFF switch on the dash. The IGnition wire to the alternator was, as usual, disconnected from the alternator and I connected the alternator end of that wire (the wire coming out of the alternator two-pin plug) to ground, via a 5w light bulb. The bulb lit and the battery voltage dropped to 12.7v, but the bulb did not extinguish, and when I disconnected the bulb from ground again the voltage went right back up to 14.5v.

I then tried a higher wattage bulb. Unfortunately (doh!) the only other bulb I had was a 55w headlight bulb. That didn't light at all, but after that the alternator was putting out power all the time, regardless of whether the IGnition wire was connected to the alternator or not. Even after switching off the engine and restarting, the alternator was putting out power as if the field winding was getting current from somewhere other than the IGnition wire. Also, from that point on, grounding that wire via a 5w bulb did NOT light the bulb any more.

I then found that there was a 'parasitic drain' on the battery of about 800mA with ignition key out. (It was about 25mA when I'd measured it a few months back.) Sure enough, there was also about 800mA travelling down the main alternator output wire with everything supposedly 'off'. So somehow I must have blown/shorted at least one diode in the alternator by dragging more current through it than it could take. I'm not too sure on the exact circuitry inside the alternator so I'm guessing somewhat, but in any case a diode has certainly blown (whether I blew it or not, but I guess I must have done) and if a diode has blown then as well as a parasitic load (and 800mA is MASSIVE) there is also the risk that the alternator could be putting out AC current, which would damage the battery and possibly damage other components too. So in any case I need a new alternator.

Temporarily, I have disconnected all the wires from the altenator except the ground strap (being very, very careful to insulate the main fat output wire, as that runs direct to the battery and I don't think it is fuse-protected in any meaningful way!)

Ah well, I was experimenting, and sometimes experiments go wrong. I did try to learn as much as I could about what I was doing before going ahead with my test, but I didn't really find much online to help me. It's not actually that bad: I replaced a faulty alternator a year or so ago and it was neither expensive (a used alternator from an excellent company called StevensVWspares for £40 delivered) nor was it difficult. I am optimistic that changing it again will be even easier, and no more expensive.

I know I can safely leave the alternator field wire (IGnition wire) disconnected to disable the alternator, or disconnect it and reconnect it via a switch on the dash, because that connection and disconnection is something that happens anyway when you turn the key. I'm not really introducing any novel circuitry there, nor asking any component to experience any voltage or current it doesn't ordinarily experience. But shorting the alternator to ground via that wire is something else entirely. I knew I was taking a chance, ...and I lucked out.

It would have been cool to be able to switch OFF a running alternator, but it seems I can't do that after all. It would have been cool, and that might have opened up the possibility of charging the battery when braking or when slowing down in gear with my foot off the accelerator pedal, but in fact the most important thing is to be able to switch the alternator back ON if battery voltage gets too low, and to be able to do that without having to stop and duck under the bonnet with the engine running to reconnect the IGnition wire, possibly in the dark and in the rain with other traffic zooming by. Once I've got a new alternator in there I'll fit that switch so I can re-enable the alternator while driving along. If I really want to stop the alternator I can always kill the engine for a few seconds and then restart it.

So, not a great day!

However, now I have no alternator - and it will take a few days to get hold of a new one - I am using this slight emergency to prompt me to get the auxilliary 'donor' battery system finally installed in the rear so I have more confidence that I won't be stranded in the next few days with a totally dead car.

One other thing (things have not been going so well lately!) is that the 90Ah AGM starter battery I bought six months ago has been showing signs of losing capacity in the last couple of weeks.

I guess it is POSSIBLE that there was a fault with the alternator before I killed it by experimenting. (Probably not.) That 800mA parasitic drain for example might have been going on for a while, and might have been giving me the impression that the battery was failing. More likely the battery was just not up to the job of 25% - 50% daily discharges. It was very cheap. Still, it came with a 4-year warranty and the seller sounds like he's going to honour the warranty. I may get him to send me a proper deep-cycle-capable battery instead though (to use as a starter battery) and I will pay the difference. I'm thinking of an Odyssey Extreme PC1220 70Ah battery, which can apparently cope with 400 cycles down to 80% DOD, so should laugh in the face of 25% daily discharges, and should last for years. (With a deep cycle 'donor battery' running via the dc/dc converter as well as a deep-cycle battery under the bonnet, neither battery will be discharged more than 25% under my daily driving pattern.)

......

[oldtamiyaphile]

If only it would be possible to fit a Bluemotion alt while you're at it, I guess it would need an appropriate CAN signal to work though?

[California98Civic]

Sorry! But I also say, thanks! I love the reports of failed efforts. It's also a chance to learn about the components. On your battery troubles, does your battery have a metal jacket to help it resist engine heat that can degrade the battery? I had an odyssey battery without that jacket and it eventually began showing voltage problems when the car warmed up. I got a warranty replacement/upgrade for another with the jacket and all has been well for like forever.

[Jyden]

How about starting a fuel log here, so we can follow the prograss? Nice mods by the way....

[Jyden]

Originally Posted by paulgato

But now I have a problem. My car's dash display only shows a trip average of up to 99.9mpg. I'm regularly exceeding that since I stopped using the alternator, and as the weather warms up that will go even higher. I think I can change my car's display (using VAGCOM on a laptop?) to show litres/100km instead of mpg, and I can't see there would be any such display limit in that case, as the figure would be going down with better efficiency rather than up. I may have to do that soon!

Get a scangauge or ultra gauge.

[paulgato]

Jyden, thanks, but a Scanguage is one more thing to have to buy and wire in. I will resist the temptation for a while longer. I can still see momentary or real time mpg up to 199mpg on the dash, and monitoring my fuel bills and odometer readings is the most accurate way to see overall average mpg. It's just occasional trips that have a displayed average over 99.9mpg on the dash display now. The overall average is reading in the low 90's, although that corresponds to about 80mpg as measured via fuel bills and odometer readings. Changing the display to read km/litre or litres/100km would be free (or cheaper - I'd have to pay $99 for the full version of the VAGCOM software, but I want that anyway as it will enable me to modify other behaviours of the car too, like idle speed and so on.)

As for the fuel log, I have one at fuelly.com. I'll see if i can link to it...



And Clifornia98Civic, that's a great tip about the metal jacket for the Odyssey battery, as my engine bay temperatures do get pretty high now that I have an almost 100% grille block. (Well, I've measured 50 degrees C on occasion, but not much higher than that.) In their sales blurb Odyssey claim an 80 degrees C maximum temperature rating for their batteries, but it's only when you read in more detail you see the maximum is 40 degrees without the metal jacket. I'll definitely look into that. I was under the impression that high temperatures are a problem with AGM batteries mainly when being charged, and since I mainly charge the battery with the engine off (with a temperature-compensating battery charger) I was not going to bother with the metal jacket. Also, the VW Golf battery is fully enclosed in a plastic box anyway. But your experience is leaning me towards taking the issue more seriously. Maybe my existing AGM battery is suffering its premature loss of capacity because of engine bay heat? How much additional space does the FMJ take up? Will it still fit in the battery tray/box in the same way? If not, then perhaps I am better off trying to improve the heat-shielding capability of the existing VW battery box (with heavy metal foil on the outside for example? ...or by applying that Dynamat stuff?)

Another possibility I am seriously considering now is to use TWO parallel 100Ah deep cycle batteries in the spare wheel well, and use a supercapacitor array in the engine bay in place of a battery for engine starting and for other peak current demands. No overheating issues in the spare wheel well. I'd also get a second 12A DC/DC converter and wire it in parallel so I'd have at least 25A at 14v available. (Actual output of this unit is 13.5A in fact, and they are designed to be used in parallel like that.)

Maxwell Boostcaps have a maximum environmental temperature rating of 65 degrees C and should outlive a vehicle by some margin in engine bay conditions. In the first instance I could use a standard, (already owned!) small-ish non-AGM (therefore more heat tolerant) battery under the bonnet and rely on the two large batteries in the rear for cycling, switching the alternator back on when the starter battery/supercapacitor array voltage starts to drop, ...which would only happen very rarely on longer trips as the voltage would remain up at 13-14v for many hours. For daytime driving with no wiper/blower/headlights I'd get 12-15 hours' use at 8A, and even on a rainy night I'd get 3-4 hours' use at 24A.) I'm going to install the first 100Ah Yuasa deep cycle battery in the spare wheel well today and I am going to make space for a second one in there as well, so I can just slot another in there later.