LiFePo Starter Battery In Mitsubishi Mirage 1.2

[oldtamiyaphile]

Originally Posted by cr45

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.

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.

[cr45]

Originally Posted by oldtamiyaphile

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%).

This sounds good!

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

[cr45]

Originally Posted by oldtamiyaphile

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.

Is this for a LiFePo piggybacked with Ultra Capacitors?

[oldtamiyaphile]

Originally Posted by cr45

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.

[cr45]

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.

[Hersbird]

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.

[teoman]

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.

[cr45]

Originally Posted by teoman

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.

[oldtamiyaphile]

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).



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.

[cr45]

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.