Jeep Wrangler 4xe Forum banner
1 - 4 of 4 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter · #1 ·
So complete scenario that has happened 5-6 times now.

My drive to work is 6 miles of city stop and go (no more than 50mph) and then a stretch of 15 miles on openhighway followed by 2 miles of stop and go.

I normally make this trek in electric mode only.

I have driven this path at 65-70mph and made it on pure electric but about 1/2 of the time I choose to go with the flow of traffic and do 75-80mph.

Everytime I do 75-80 the ICE kicks on when there is 6-7 miles of range left in the batteries?? and then when I exit the freeway it will go back to electric only.

Any ideas what is causing it to kick on??
 

·
Registered
Joined
·
102 Posts
Think about what your battery voltage is as you approach the end of it's capacity. It's dropped considerably and requires more amperage to provide the same power (wattage) output. So when you're already low, it's pulling harder and the voltage drops even more. So...you're trying to pull enough juice to push a brick at 80mph and it just doesn't have the power so the ICE kicks in.

To be more technical: Power=Voltage x Current. Voltage is around 400v when fully charged. So it should be around 260v or so when almost depleted or about 300v or so when you're at 6-7 miles left in the tank. If the power needed to keep 80mph was 100hp which is 100hp x 745watts/hp = 7450 watts and you're only at 300v then you need 24.8A to maintain that speed. Unfortunately batteries have internal resistance which means the harder you pull on them the lower the voltage is so you're actual voltage under load is probably 250v and your amperage is now knocking on the door of 30A. Here is where your problem comes into play! The low voltage cut off for manganese cobalt batteries is 2.5v per cell. So when you start to hit around 250v then the system turns off. When you stop pulling amps then the voltage goes back up and you can use the electric motor again until you pull hard enough to get back down to low voltage cutoff. Low voltage cutoff kicks on more and more the closer you get to 0%. Jeep claims they leave some in the system so you don't over discharge and that's a REALLY good thing because batteries get very hot when they're overdischarged and they swell and bad things happen.

I hope that wasn't too much information but that's the problem in a nutshell. :)

Try staying under 70mph and you shouldn't have an issue. Someone posted a while back, after doing a LOT of testing, that efficiency goes downhill exponentially once you hit 70mph.
 

·
Registered
Joined
·
21 Posts
Discussion Starter · #3 · (Edited)
Think about what your battery voltage is as you approach the end of it's capacity. It's dropped considerably and requires more amperage to provide the same power (wattage) output. So when you're already low, it's pulling harder and the voltage drops even more. So...you're trying to pull enough juice to push a brick at 80mph and it just doesn't have the power so the ICE kicks in.

Try staying under 70mph and you shouldn't have an issue. Someone posted a while back, after doing a LOT of testing, that efficiency goes downhill exponentially once you hit 70mph.
Makes sense - I was thinking due to the higher speeds that it might be a heat issue also for the batteries? Maybe a protection built into the software due to the higher draw I was putting on them.
 

·
Registered
Joined
·
102 Posts
Sorry, I made a few edits after the original. But you're mostly correct in that higher amp draws cause more heat and more heat increases resistance which drops voltage which requires more current which reduces voltage....it's like a dog chasing it's tail. :)
 
1 - 4 of 4 Posts
Top