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It's about 16 deg F today. First time using the car in this cold weather. Started the morning commute with battery about 2 bars from full. It agressively charged to full by the time I had gotten to the highway ~3 miles. It continued to charge much of the trip to work any time I was part throttle I had about 3 bars of charge. So I guess it's doing that trying to put some heat in the battery. Once I realized that I shut off the aux fans I have blowing into the battery cooling duct behind passenger seat. So now the battery is balanced I guess. Only managed 67 mpg on way to work this morning. Probably going to full lower grill block tomorrow.
David
 

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It's about 16 deg F today. First time using the car in this cold weather. Started the morning commute with battery about 2 bars from full. It agressively charged to full by the time I had gotten to the highway ~3 miles. It continued to charge much of the trip to work any time I was part throttle I had about 3 bars of charge. So I guess it's doing that trying to put some heat in the battery. Once I realized that I shut off the aux fans I have blowing into the battery cooling duct behind passenger seat. So now the battery is balanced I guess. Only managed 67 mpg on way to work this morning. Probably going to full lower grill block tomorrow.
David
I've noticed mine seems to do that as well - aggressive charging when it's cold out.
 

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Hypermiler
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Yep, different behavior in cold weather. Assist and regen act differently and are limited somewhat.

If you have an obd type device that will read ima stuff, it will indicate the pack fan running in low speed (a person with good hearing will hear the fan in low). If you can command the pack fan on, even better. Good way to draw cabin heat through the pack to warm it up. Once pack temp gets back over 40 F, things go back to normal.

Come on spring :)
 

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It continued to charge much of the trip to work any time I was part throttle I had about 3 bars of charge....So now the battery is balanced I guess.
If that were a question it'd be a pretty good one. I've only seen this kind of thing once before, so not much opportunity to assess, and I can't remember what exactly it did. If the car 'just keeps charging' - no major voltage limitation (such as around 17.2V per tap) and no absolute state of charge/amp-hour cutoff - seems like, yeah, it would balance. But if there's voltage or SoC/Ah limits then it wouldn't balance much or as much...

Under these cold circumstances the question is mainly about whether the car allows one tap to reach 100% full yet continues charging anyway. Normally it would stop charging...

My guess is that the background charge is probably around 6-7 amps and, if so, I wouldn't expect to get much balancing unless I saw a pack voltage around at least 184 volts (probably even higher as the cells will probably still be cool, which means you'd need a higher voltage to reach full charge). So, if anyone's seeing this cold behavior and has an OBDIIC&C, you might want to keep an eye on pack voltage and current -- if you want to know whether there's bonafide balancing going on... Maybe watch temp, too, as you should be seeing temp increase noticeably faster once more cells reach a true 100% full...

It's actually pretty interesting, cuz if there were a way to trigger the cold charge routine we might have an on-board means to balance...

Hmm, now I wonder: If we were to spoof pack temp to something cold, wouldn't that trigger the cold charge routine?
 

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Hypermiler
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OBDIIC&C displays a cold background charge of 10-12 amps on my red (and did on the silver also before the pack bypass). Perhaps being a bit to worrisome, I use IMAC&C to back that off to about 6 amps.

If I let the car do it's thing at 12 amps, the pack tops out on voltage and soc of 81% fairly quick and the background stops for a short period. Regen braking really runs up the voltage fast.

Everything I've read here (and seen on my cars) is the pack doesn't accept charge very well when it's cold. I go for the 'warm-up' (pack fan and cabin heat) to get the pack over 40 deg F (preferably over 50) before I let the car dump higher amps into the pack, including regen braking. Imac allows me to shut off all regen braking.
 

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If I let the car do it's thing at 12 amps, the pack tops out on voltage and soc of 81% fairly quick and the background stops for a short period....
Does it ever go over 81% though? It's sounding like the cold weather background charge is just charging to full and quitting, so no real balancing...
 

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It won't go over 80%, as it is G1.
Max. V maybe 174 but the system will discharge back to around 165V real quick.

HTH
Willie
 

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Hypermiler
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Does it ever go over 81% though? It's sounding like the cold weather background charge is just charging to full and quitting, so no real balancing...
Correct, no balancing. The car's way of self warming the pack.

The draw-back is if the pack is already well charged, the voltage and soc peaks quickly. I've seen it go to 82% a couple times. As it approaches 82, the regen amps taper off to zero.
 

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Have you (or anyone else) ever tried to reset SoC low (or rather to medium, 60%) with the OBD2CC during one of these cold charging intervals? I wonder if nominal state of charge alone is what triggers the termination. If that were the case the BCM/MCM might allow a higher tap voltage than normal - if you reset SoC lower... I kind of doubt it though... Willie mentioned 174V, most likely resting voltage after the charge quits, which sounds pretty normal...

I wouldn't worry too much about the charging doing any harm as long as the loaded total voltage remains below about 186V; 1.53V at the cell level is about the voltage at 6.5 amps at which the cells are near 100% full, at normal room temp and, of course, with decent cells. So cool/cold at say 10-12 amps you'd see a bit higher voltage at the same charge state, around 1.55V / cell or 186V for the pack I think would be a decent rough estimate, conservative, safe... The car itself allows up to 19 or 19.2V at the tap level, regardless of current rate... Overall, I'm pretty sure that, as long as voltage remains in check, the cells are coping with the charge rate and little untoward damage is happening... On the other hand, the monitoring is happening at the 2 stick level, so any 1 cell with a relatively higher voltage could slip through the cracks...

edit: actually, just bumped into the OEM graph of charge at different temps, and the full voltage at 1C rate is 1.6V at 0 degrees C - so there's our 192V figure right there...
 

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I've been using reset a lot lately - it's ... illuminating seeing just how much I can futz with that and not have it interfere with normal operation...

The car's way of self warming the pack.
One thing that's interesting about what appears to be the car's warming routine is that it really doesn't do much to warm. If you're at say 75% SoC and it allows charging to ~81% - big deal, not much warming there. Even if it were at 60% there's still not much warming that's gonna happen. So, I wonder how much it's for warming and how much it's just to make sure the pack is charged to normal car-full... If it were really a warming routine, you'd think it'd charge to a true full. Technically, that should be doable without much if any harm to the NiMH cells, say, to allow a gentle overcharge. The emerging fact that it doesn't do this makes me think it's more about getting the pack charged full rather than warming...
 
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