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Spontaneous charging


Hardp
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Recently, while in the highlands of Nova Scotia, not having plugged in my energi for about 2 weeks, we were coming down off a mountain. I rode the brake and it charged the battery in hybrid mode but after another minute, it switched over to plug in mode and I charged it enough for 8 EV miles.

 

This happened a 2nd time about an hour later.

 

I thought plug-in EV miles can only be achieved via a wall outlet, bit apparently not.

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Didn't someone calculate that Regen charging could actually charge the battery faster then a 110 outlet as well?

 

Regen charges faster than 240... I think Larryh calculated regen to be >20kw, so if you applied that amount of energy going downhill from a mountain, you could charge the pack really quick... like 20 - 30 minutes quick.

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Max regen is 35 kW.  The 120 V charger only supplies 1 kW.  You need about 5.8 kWh of energy to charge a depleted battery.   If the car and contents weigh 1870 Kg, that would mean a descent of at least 1138 meters, or 0.7 miles.  But regen isn't 100% efficient, so you will need more energy than that.  Depending on how fast you go down the hill, you might capture 60%.  That would mean a descent of at least 1.2 miles.  I'm not sure if the car can accept a sustained regen of 35 kW for a long period of time. 

Edited by larryh
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I'm not sure if the car can accept a sustained regen of 35 kW for a long period of time. 

I imagine that at that level of charging the HVB would heat up very quickly. Once it gets too hot it will reduce the max charge rate. Next time we do a road trip through the mountains I'll be able to find out.

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  • 2 weeks later...

I agree, with the charge rate so much higher, the battery temp might rise to a point where the engine would get started to hold the car back down the hill but its just a guess.

 

If the battery cells are 25ah, and the nominal voltage is around 310.8v, then going down a hill charging at 30-35kw would mean you're charging the pack at around 4C or 97-113 amps.

 

4C is generally high by industry standards for Li-ion packs, so due to this while I would love to recharge my car's pack in 20 minutes going down MT. Washington, I'm not sure its the best exercise for it.  Ford limited the L2 charge to 3300w for a reason, as they could have easily made it accept 6600w like the Focus for example and have it charge in 1 hour instead of 2, but then again it was most likely done for the longer life of the battery.

 

-=>Raja.

Edited by rbort
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murphy, on 02 Oct 2014 - 03:56 AM, said:

I think that I read that the Focus battery is liquid cooled while the Energi battery is air cooled.

That is correct. The Focus appears to not let the battery get hotter than 98F with its thermal management. The Energi battery gets hotter than that quite frequently.

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