LiFePo Starter Battery In Mitsubishi Mirage 1.2
 

The original battery would appear to be on the way out in my 2014 1.2 3cyl Mirage.

After a 151 mile trip yesterday, the battery is measuring 12.4 volts today - approx 15 hrs later - and a hydrometer test indicates a specific gravity of 1.2 for all 6 cells.

The battery seems quite big for a 1.2 SI engine - 66AH and CCA 520 - but I assume this is because this vehicle has stop start.

During my trip, the battery was being charged approx 95% of the time.

I would assume that this is hurting my mpg though the average was a respectable 60.37 US # 72.5 IMP # 3.9 lit/100km.

Any advice on selecting a battery?

This is one candidate https://www.ev-power.eu/LiFeYPO4-bat...0AH.html?cur=1

http://ecomodder.com/forum/attachmen...7&d=1521643862

Just keep in mind LiFePO4 doesn't tolerate charging below freezing, so if you plan to use it in freezing temps it would be better to locate the battery inside the vehicle. This would probably require using a supercapacitor bank in the engine bay to provide the CCA the starter motor needs. You could downsize your battery if you go with a LiFePO4 and super capacitor bank. What is the electrical draw while the engine is off?

You'll probably never tell the difference in MPG though.

What size of LifePo and Capacitors would you suggest?

The weight reduction would be nice as this car is already quite light at 845 kg.

I would suggest none. Unless you plan to relocate the battery to the interior and bring it in at night.
LiFePO4 is bad for cool climates and under hood temp will kill them in short order.

As oil pan says, this is likely more hassle than it's worth considering the temperature sensitivity.

If I were to tackle this project I'd start by measuring typical electrical draw while the engine is off. This would determine what size battery to run, but I wouldn't go less than 20 Ah. I always recommend this 20 Ah pack:

LiFePO4 Prismatic Battery: 12.8V 20Ah (256Wh, 10C rate) (24.0) - UN38.3 Passed (DGR)

As far as capacitors go, you can probably start the vehicle using 6 series connected Maxwell 350 F caps.

https://www.ebay.com/i/302040184049?chn=ps&dispItem=1

You would connect the cabin located LiFePO4 in parallel to the caps that live in the engine bay, possibly with a very low ohm current limiting resistor. The resistor would force the caps to do the majority of the heavy lifting to prevent the wires and LiFePO4 from overcurrent.

Basic concept of the idea is in my video here:

https://www.youtube.com/watch?v=LX_o...ature=youtu.be

Remember I have been using LiFePO4 starting batteries since 2010, I live in new Mexico which has pretty mild winters and I know all about their cold sensitivity.
If someone in a cold climate switches over to them, learns everything the hard way they will be very disappointed and switch back to lead acid with in a year.

The battery has to be located away from engine heat, which means most people will have to relocate it and needs to be brought inside at night when the temperature drops down near freezing.

I don't think they are more hassle than they are worth but I was prepared to relocate the battery and bring it in on frosty nights.
The batteries have lasted far longer than any lead acid, but I take real good care of them.

Redpoint, Oilpan,

Any reason to be concerned that the OEM alternator was not designed for lithium? I understand such smart alternators will deliver voltage that is incorrect. I imagine if you kept the alt off most of the time and charger from the grid through a proper charger, using alt only as a range extender, one could get better life/service out of a lithium.

I'm on year 3 of running one in the Prius. The battery was already located in the cabin, so it was simple to replace. I don't bring it in when it's freezing and take no special precautions to protect it. Since the Prius doesn't use the battery to start the engine, the loads are relatively low. No supercap required.

The prius is ideal then.

I believe the smart alternators charge the LiFePO4 batteries to a more desirable level, to around 90%. Where dumb alternators can try to change them to 100% every time.

Max voltage for LiFePO4 is rated at 14.8v, so a dumb alternator charging to 14.3 - 14.4v should be fine.

I run the same battery in my jetski (3 summers so far) with no special considerations.

Any alternative chemistry will kill your OEM stop start unless you have the abilities to hack and reprogram it.

However if you do all highway miles where S/S doesn't matter (or your car allows you to key off manually - most S/S cars don't really like that), the economy gains are impressive (~10%).

You're looking for a 14.4Ah battery ideally. The car will start easily on 7.2Ah, but the peak charge current coming off the alternator is a bit too close for comfort, especially on 'smart' alternators.

I don't think it's essential to relocate the battery, as a hypermiler your underbonnet temps should be just about LiFe friendly. OE batteries are already located with cooling in mind.

Sub zero temps, you're on your own though.

Another simple thing you can do is grid charge the OE battery regularly. That way the alt will stay off for the first several miles of your trip.

This sounds good!

There is a button for switching of S/S though it has to be pushed for every trip.

Is this for a LiFePo piggybacked with Ultra Capacitors?

While I do run supercaps, that's just because I have them, not because they're needed. 7.4Ah starts and runs the car fine, but might be a little close for comfort in a daily driver. It would be very easy to kill a battery that size if any accessories were left on for any period of time.

On previous cars (admittedly with Pb batteries), I've found that while the supercaps help cold cranking, once you stop cranking they suck so much current from the electrical system that the engine sputters (possibly starving the ignition coils). Three of the four cars (old and new -big and small) I tried them on had this problem.

Only happens on the first start of the morning though, after that starting performance was improved.

Point is while supercaps can help smooth out peak current demands, they can present a massive current demand themselves.

Smart alts present challenges of their own.

The smart alt on my 875cc Fiat is rated for a max output of 160A! Well above what such a car would normally have. LiFe batteries have a max charge rating of 30A per 7.4Ah. You'd need quite a big battery to safely accept the full alternator output.

You might also find the alternator is no longer 'smart' once you change chemistry, because the internal resistance readings will be well out of spec. The alt might go into fail safe mode (just holding 13.8v) - this would be a good thing as you wouldn't see full alt output under braking. From memory, my Fiat's alt still worked correctly with the LiFe.

On the other hand, Lotus sells a LiFe option for it's Elise (14.4Ah I think). I'm fairly certain that it comes with a Toyota/Denso smart alt and that it's highly unlikely that they do any reprogramming.

Many thanks for the very useful input from posters.

As the EFB batteries this car uses are very expensive, I shall replace the present original battery with either an ordinary lead acid or a 40AH LiFePo in the next 2 months.

Present battery only holds 12.2 volts but have not had any issues starting. Maybe it is the sheer size of the thing.

I have experimented with the stop/start switched both on and off and I am not seeing any difference in fuel economy almost certainly due to the fact I rarely ever stop.

When coasting in gear with the stop/start activated I can feel the car slowing down more rapidly than when the stop/start is not activated. The battery voltage climbs from 12.2 to 14.5 volts during this period.

I have just run a full tank of fuel through the car and the mpg via in car meter is 60.8 US / 73 IMP.
The calculated MPG is 62.9 US / 75.5 IMP.

This would appear to tie in with other posters comments that the car computer under reports mpg.

All in all this is one serious ECO car.

I have 2 relatives in Toyota Auris and Yaris Hybrids that have never seen these figures.

It's the cold temp problem only a charging problem? They can be used in cold temps, just not charged was what I understood. So as long as it is charged up before shutting off, and inside the car warm car it may be frozen the next morning but it would still start and then once warmed up inside the car could be charged again.

More or less yes.

On another forum, they turn on the lights for half a minute to get the lithium battery warmed up, the it starts motorbikes just fine.

It was on learning that piece of information that got me to thinking that LiFePo should be up to the job.

The large 1 litre motorcycles are using LiFePo batteries these days and they are often only 10 Ah.

Also the LiFePo battery - linked in first post - is okay up to 80 deg C under hood temperature which for a country that never gets above 25 deg C at the height of summer should be no problem.

I am happy to charge the battery the odd time from the mains.

A change to this 40 Ah LiFePo battery would save 17 lbs in weight.

You don't NEED a s/s battery in a s/s car. The OE battery in my Fiat was an s/s type, massive and very heavy, but only 64Ah capacity.

The break down guy replaced it under warranty with a standard battery - same physical size/ weight, but around 120Ah capacity.

I've been running that way for a couple of years and it works fine. Makes me wonder if s/s batteries are a con. Running a battery that you normally find cranking a V8 in a sub 1 litre car should mean a long life.

If you rarely stop, there's really no reason to run an S/S battery. You could run a much smaller conventional battery (possibly at a shorter life), or a big conventional battery (S/S still works on my car).

:turtle:

The economy gains from LiFe come primarily from their improved charge efficiency. If I took my Pb battery car, mains charged it to float then drove around the block, it would take around 20mins of mains charging to bring it back to float (essentially ~3Ah of capacity vanished on every start). That's why normally I'd charge it once a week and it would take up to 2 hours (~14Ah) to come to float.

With the LiFe, the battery is always 100% charged. No need for mains charging at all (charger shuts off immediately when connected). No charging losses as it approaches full, unlike Pb. I got a decent gain in low end power from the alt noticeably having less work to do.

Even on a cold start, because the alternator keeps the battery 100% full, the battery won't really be receiving a charge to speak of.

A second of cranking only takes about 0.2Wh out of your battery. Your car should also start much faster on LiFe. My LiFe maintains nearly 13v while cranking, even a healthy Pb sags to 12v or less.

Cold charging is a problem for EV's and alt deletes and the like charging from a low SOC. Any charge from a near full SOC shouldn't present a problem.

Weighed the rear seat today.

Double Rear Back 11.2 kG
Single Rear Back 5.2 kG
Actual Rear Seat 3.4 kG

Total 19.8 kG / 43.7 lbs

I shall drive around for a while with the seat backs removed but actual seat in place.

Using my Ultra Gauge, I have taken some fuel flow rates at a selection of idle speeds.

Engine Fuel MAP
Speed Flow
(rpm) (G/hr) (psi)
750 0.14 3.8
1000 0.17 3.48
1250 0.21 3.34
1500 0.23 3.05
1750 0.29 3.19
2000 0.31 3.19

As my car has a MAP sensor with no MAF, the Ultra Gauge appears to assign a VE of 75% across the whole load/speed range and then calculates the air flow based on the manifold air density and this assumed VE. The fuel flow is then proportional to the air flow.

I am curious if any North American owners have measured idle fuel flows as their cars have a MAF sensor and thus the fuel numbers should be more accurate?

Mirror Delete
 

Deleted passenger mirror today and subsequently got a new mpg best on a 14 mile out and back trip that I have driven approx 10 times in this car. I always glide on down slopes when I can on this route as the traffic is very light.

New best 69.11 mpg US / 83 mpg IMP / 3.4 lit/100km

Engine started from cold - 62 oF water temp

Previous best on this route was 64.95 mpg US / 78 mpg IMP

The car appeared to glide with less retardation in speed compared to normal.

Just need some white insulation tape now to replace the green!

Nice updates. Instead of tape, you might make a filler plate out of a white or gray plastic, prime it, and paint it an OEM white if you want maximum stealth. Alternately, a black plate to look like trim. There are examples of the builds already on EM. Search top left.

Did you get the lithium? How is it going?

New Absolute best mpg - 76.44 US mpg
 

Noticed there was next to no wind this evening and decided to take the car on a 22 mile circular route - non stop.

Used pulse and glide and a 42 mph top speed.

Engine was idling during glides.

Parked up on 76.44 mpg US / 91.8 mpg IMP / 3.077 lit/100 km

This is equivalent to a diesel doing 2.797 lit/100 km from both a thermal efficiency and a CO2 point of view.