Hot battery warning... but kinda doesn't make sense

[WattsUp]

I drove my FFE today on a 130-mile round-trip, with a charge-to-full in the middle on 240V. Ambient temps during the drive were 75-85 and I had the A/C on for both legs. The ambient temp during that mid-trip recharge was in the 80s.

Everything was fine until tonight. When I got home, I put the car on the 120V charger to top it off a bit for my morning commute, after which I intended to charge up fully at work. So, I unplugged it after 2-3 hours.

A hour or so after unplugging I get a text saying, "Matt's EV has a hot battery, which will limit the vehicle performance. Please plug Matt's EV in to bring the battery temperatures to optimum operating range". Huh? The car hadn't been charging for an hour at the point I received the warning text, plus the ambient temp is 60 (surely not a "severe" circumstance for the battery management system).

I went and plugged it back in as asked (on 120V), expecting the fans to come on something. But, nothing. The relays clicked and the charging ring lit up. And now the website just says, meh... it's charging, with the same end-of-charge estimate as when I first plugged it in (before it had decided it was "too hot").

So... is the battery hot or not? I would have expected more (e.g., fans coming on). Or, the overall charging estimate to be extended (to allow time for cooling).

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Edit: Well, one thing did happen. Shortly after plugging back in, the red "Battery Performance: Poor" status (which had been displayed in the "Vehicle Info" section of the MFM website) changed to a green "Battery Performance: Good" status.

 

[kmaluo]

Same thing happened to me. I know the cooling system doesn't come on when using 120V. Maybe your battery was hot right after the trip and the car gave you a delayed error when the hot battery started charging without cooling.

 

[jmueller065]

Do you really know the cooling system didn't come on?

I'm asking because one time this past week after plugging mine in I noticed the fan was on (even though it was a cool night, etc. much like your above post).

So I opened the hood and watched it. After a few minutes the fan stepped down in speed a couple of times for a few minutes each time before completely shutting off--e.g. it is a variable speed fan. Thus it could have turned on at a low speed--not fast enough to hear. Granted if you got the hot battery warning I would expect a full-blast fan.

 

[WattsUp]

Strange, mine's plugged in (120V) right now with the outside car temp reported as 93 degrees F, but no fan. And this immediately following quite a bit of driving (down to 10% battery remaining) earlier today in similar temperatures.

I did get a dash message ("It's hot outside. Plug the car in when not in use.") when I came home and parked, but so far no "hot battery" text warnings, and the MFM website says the battery condition is good.

I've definitely (and so far only ever) heard the fans coming on and off when plugged into 240V.

 

[philly_ev]

"It's hot outside. Plug the car in when not in use."

So when it's hot out the FFE should be plugged in even when not charging? Is this to allow the fans to run?

 

[WindPowered]

Strange, mine's plugged in (120V) right now with the outside car temp reported as 93 degrees F, but no fan. And this immediately following quite a bit of driving (down to 10% battery remaining) earlier today in similar temperatures.

I don't find this entirely strange. 120V is moving a relatively small amount of current (12A) through the battery, so there isn't nearly as much heat generated by this as opposed to when you're driving and drawing much more. Also, you were at a very low state of charge so the internal resistance of the battery was low, meaning even less heat was generated by the charging. I would wager that even though you had just driven, your battery was actually cooling down naturally while charging at 120V.

Keep in mind, the heat generated by the flow of current is what the active cooling system is primarily designed to handle (e.g. when you're either charging or driving). Ambient heat (non-operating) is a very minor factor. Ambient heat while operating is only a concern because the heat generated by the current flow can't dissipate as easily due to to the higher ambient temperature, thus the need for the fans and radiator.

I've definitely (and so far only ever) heard the fans coming on and off when plugged into 240V.

This makes sense to me. At 240V/30A you're moving a significant amount of current, and thus generating significant heat. Again, the active cooling system is going to come on primarily during significant flow of current, irrespective of moderate ambient temperatures.


WP