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Old 10-14-2017, 01:51 AM   #311 (permalink)
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If a LiFePO4 needs to be jumped, then it's probably already toast. I've killed a 4.2 Ah battery just in the time it took to measure various electrical loads with the engine off; probably 15 minutes of testing. I would only recommend a 4.2 Ah battery for vehicles with very modest electrical requirements and parasitic drains, such as a motorcycle. 20 mA is a common parasitic drain (car off and parked), and that would give about 1 week of standby time and not leave enough charge left to start the vehicle.

I consider 20 Ah to be minimum for most vehicles. This would allow engine off coasting, listening to the radio with the car off, or parking the vehicle for several weeks.

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Old 10-14-2017, 08:38 AM   #312 (permalink)
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Quote:
Originally Posted by redpoint5 View Post
If a LiFePO4 needs to be jumped, then it's probably already toast.
Yeah, I know that. I was thinking from an OEM perspective, if they started fitting LiFe at some point someone would try jump starting one. AFAIK only the 911 GT3 RS is available with a LiFe option.

My first attempt in the Fiat died as two weeks of standby draw killed the battery. New cars have pretty crazy standby currents, closer to 50mah from memory.

So far so good running 14.4Ah in the Proton though, even with extensive EOC, but I'm certainly mindful of keeping an eye in it. It's an almost daily driver which helps. With so little capacity and such good charge efficiency, the alt seems really effective at keeping the battery 100% full.

The plan was an alt delete and 400W of solar panels, but enough LiFe to store that current could be expensive. I may well still have to go to a deep cycle Pb. Or just stick with the alt, LiFe, and a smaller solar panel.

A 10% gain is amazing, same as what Darrin reported with a full alt delete. I'm not sure how much might still be on the table with a full delete.
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Old 10-14-2017, 09:00 AM   #313 (permalink)
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%10 is fairly amazing.

I wonder how that would change if you are really using the electrical stuff in the car. Obviously it will go up. Ut will that %10 efficiency still be maintained?
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Old 10-14-2017, 09:08 AM   #314 (permalink)
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This car does a lot of short trips. That's why I think I'm getting this almost indecent gain.

With a Pb, every time you park for 10 mins, it's like someone is sucking 2A out of your battery. When you start again, the alt then works hard to replace that 2A (at very low efficiency), only for you to stop again and all that hard work evaporates.

EOC probably has the same effect.

If you drive steady on the highway, you might get different results.
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Old 10-14-2017, 09:15 AM   #315 (permalink)
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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.
I think it would be wise to bolt on a charger like the imax or charging harness with diodes and resistors not to kill the lithium battery. Also if it nees a jump start i think that the battery is already dead.

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