Replace your car battery with capacitors!

[oldtamiyaphile]

With a couple of days running the Li-Fe, I'm seeing a 10% improvement in economy. MPGuino was sitting on just under 6l/100km for the tank, now sitting at 5.5 (tank data reset with the battery disconnect).

I hooked up my battery charger to see how full the alt is keeping the battery.

With a Pb, it would take about 20mins to charge to full even if you connected the charger immediately after turning off the engine. That's about 2Ah on my charger. In normal use, I'd connect the charger about once a week, it took about 4hours to bring the battery up to float (~30Ah).

So I connected my Li-Fe to the charger, stood there as it settled into the appropriate charge mode, and it was done within 2 mins!

I think it's clear then why the alt has less work to do. Pb batteries need to be kept full for maximum life but unfortunately their charge efficiency drops to 50% as they reach that point - a lot of wasted energy. What's really disappointing is that OEM's still aren't offering this tech in any numbers, the real world fuel savings should justify the expense for at least the 'ECO' versions of ICE cars.

PS: I have this 12v Automotive LiFe charger:

https://no.co/g7200

Much easier than messing with hobby chargers

[freddyzdead]

I, too, am getting at least 10% better fuel economy. But I can't tell how much of that is because of the battery, and how much is from ditching the E10. There's no way to find out without reversing one of those. If it's the E10, then I can see no reason to use it. The 2 cents/litre saving is no saving at all, it's the opposite. If it's the battery, then why isn't this tech being pushed a lot harder?

[freddyzdead]

@oldtamiyaphile That charger design seems a little ambitious. Is it for sure that it can unambiguously identify the chemistry of any battery you connect it to? The consequences could be unhappy if it got it wrong. e.g. distinguishing a Li-ion from a LiFePO4.

[oldtamiyaphile]

It's not quite automatic. You have to manually select the special modes. However when connected to an AGM it selects that first, and when connected to LiFe it selected that first. Of course it's always a good idea to confirm it's in the correct mode. I don't think there's too much issue if it was wrong though after all the alt isn't intended for LiFe either.

[redpoint5]

Originally Posted by oldtamiyaphile

What's really disappointing is that OEM's still aren't offering this tech in any numbers, the real world fuel savings should justify the expense for at least the 'ECO' versions of ICE cars.

LiFePO4 cannot be charged below freezing temperatures, so that eliminates most of the US for being a suitable replacement. Even in parts of the world where it doesn't freeze, it's still possible to drive the vehicle to a place that does freeze.

I've been running a LiFePO4 for about a year now in the Prius. It may be suitable in the Prius since the battery lives inside the passenger compartment and isn't used to start the engine. Instead it only has to provide power long enough to close the contactors to the traction battery. Once that happens, there is no load on the 12v battery. I'm hoping it's the last battery I'll ever buy for the Prius.

As an aside, I've run a LiFePO4 in my jetski the past 2 seasons and it works great.

My plan was to replace the failing battery in the TSX with a small LiFePO4 in the glovebox and a capacitor bank under the hood, but my dad is always quick to buy a standard battery. He's ruined my last 2 projects!

[Stubby79]

LiFeYPO4, cold-weather chemistry...if you can find any.

[oldtamiyaphile]

Originally Posted by redpoint5

LiFePO4 cannot be charged below freezing temperatures, so that eliminates most of the US for being a suitable replacement. Even in parts of the world where it doesn't freeze, it's still possible to drive the vehicle to a place that does freeze.

I also wonder what happens if you come at it with a pair of jumper leads

[redpoint5]

Originally Posted by oldtamiyaphile

I also wonder what happens if you come at it with a pair of jumper leads

Probably fine depending on the capacity. LiFePO4 has quite a high rated discharge rating. The 20 Ah battery I bought from Batteryspace is rated for 200 Amps (10C) for 10 seconds. Hobby King shows their batteries rated for 30C constant and 40C burst. That's 168 amps from a tiny 4.2 Ah battery. Get the still tiny 8.4 Ah battery and you can jumper something that draws 336 A.

I'd have no problem starting my motorcycle with just the 4.2 Ah LiFePO4 and no capacitor. I've started my 2-stroke jetski for 2 seasons with the 20 Ah pack, sometimes cranking for 30 seconds.

[oldtamiyaphile]

I mean if the LiFe is the one being jump started. The low internal resistance should mean the Pb delivers current well in excess of the LiFe's charge rating.

I don't doubt the amazing tech in these small batteries. 7.6Ah is quite enough to start a small car. I just feel safer with a bit more reserve. I also felt that the 30A charge rating of a single pack might be too close for comfort. 60A should be fine with the stock 75A alt.

[Stubby79]

Originally Posted by oldtamiyaphile

I also wonder what happens if you come at it with a pair of jumper leads

It will charge or discharge, depending on the voltage difference between the two batteries. Could be a lot of amps, depending. Not an issue, unless it's charging below freezing, or the cells are imbalanced and one of them gets driven over 3.65 volts. Discharging isn't a problem unless one or more cells gets driven below 2.7 volts.