DIY Electric Car Forums banner

1 - 20 of 37 Posts

·
Registered
Joined
·
47 Posts
Discussion Starter #1
I am wondering if many DIY'ers are designing in ways to heat and cool the batteries? I live in Oregon, and my biggest concern is probably that I may end up charging batteries during the night when the temperature is below freezing.

Similarly, I will probably be starting in the morning with a very cold pack.

I feel like I haven't seen many people on here adding temp management to their battery packs, am I mistaken?

I have power RFE-200 LiFePO4 batteries in prismatic plastic cases. My setup has a water cooled brushless DC motor, so I'm wondering if I should add a cooling/heating loop that runs back to the batteries, or perhaps even an electric heater for the batteries if cooling is not an issue?

Any advice on this, or examples of what other have done would be great.
 

·
Registered
Joined
·
1,106 Posts
Don't quote me on this, but I think lithium batteries can be discharged almost at the same rate when cold as when warm. Unless you're drag racing or you have a very short range pack, you're nowhere near maxing out your current draw even when cold.

The recharge rate is what's limited.

I'm not sure if there's a danger in charging them when cold, or, if it's just that they will refuse to charge when cold.

When charging it's an easily solveable issue because you have grid power to run a heater, so you might charge a bit slower (due to wasting energy on heat) but everything will be fine.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #3
Thanks Matt. That's kind of what I figured, but of course EV manufacturers go to some great lengths for thermal pack management so I didn't want to overlook things.

I've actually tested these batteries in a lab with the guy who designed them, and we pulled and pushed 500A from them and saw only a small amount of heating near the terminals. I can't remember exactly but I believe we ran at this rate for a few minutes. The room we were in was definitely a nice temperature though, so it's more anecdotal evidence than anything. And of course I will probably be charging at more like 30A off my 6.6kW charger.
 

·
Registered
Joined
·
742 Posts
You can turn LFP into instant scrap charging too cold.

But the cotes only get **that** cold in places I personally would avoid.

Certainly coastal Oregon should rarely be a problem.

Snow bunnies best stick to lead
 

·
Administrator
Joined
·
6,120 Posts
You can turn LFP into instant scrap charging too cold.

But the cotes only get **that** cold in places I personally would avoid.

Certainly coastal Oregon should rarely be a problem.

Snow bunnies best stick to lead
This is why the Tesla is the most popular car in that semi tropical paradise called Norway
 

·
Registered
Joined
·
742 Posts
Tesla's cell chemistry has nothing to do with LFP.

And believe me, the millions spent on engineering their "failsafe" Temp Management Systems is well spent and hard for DIYers to replicate for mobile living space House bank usage.

Any EV's range is cut to a tiny fraction in arctic temps, have a very hard time warming up, and charging is drastically slowed down.

In the recent cold snap many Tesla owners couldn't even get into their frozen cars.
 

·
Administrator
Joined
·
6,120 Posts
Tesla's cell chemistry has nothing to do with LFP.

And believe me, the millions spent on engineering their "failsafe" Temp Management Systems is well spent and hard for DIYers to replicate for mobile living space House bank usage.

Any EV's range is cut to a tiny fraction in arctic temps, have a very hard time warming up, and charging is drastically slowed down.

In the recent cold snap many Tesla owners couldn't even get into their frozen cars.
You say that but again Norway is one of the places with the most EV's
I think you have been conned by the anti EV lot
 

·
Registered
Joined
·
1,106 Posts
So, that article is from 2011.

And, IIRC Battery University has bad enough misinformation that it's been disallowed as a valid source on Wikipedia. I don't know whether that applies to this article or not.

The article makes no mention (I only skimmed) of LiFe batteries which were more common back when it was written.

It says that it's okay to charge lithium at a 50-hour rate when cold, and, that charging them generates heat.

I just ask because I've thrown some 18650s into Christmas Light displays outdoors and left them on and out overnight, in -25'C conditions, with no low-voltage protection, let them literally run themselves down to 0v, then slapped them in the charger immediately in the morning at 1A rate (0.5C), and continued to repeat this cycle for the whole Christmas season.

At the end of the season I saw about a 5% decline in battery capacity from their tested capacity at the start of the season. And they were old and used to begin with.

I kind of suspect that the capacity decline is due to discharging flat to 0v, not really the cold at all, as it's about in line with expectations from doing that.

So, while it's a small sample size, I haven't seen evidence that lithium ion batteries are ruined immediately if you charge when cold once.
 

·
Registered
Joined
·
742 Posts
You say that but again Norway is one of the places with the most EV's

I think you have been conned by the anti EV lot
That is true, have family in Norway so not news to me.

Does not change the facts I have been stating, would be foolish for people to buy into new/high tech without knowing those facts.

I am 100% pro-EV, in fact believe no other private automobiles should be legal.

So maybe address the facts you think you might be disputing instead of creating false "us vs them" ad-hominem /genetic*fallacy arguments that are completely irrelevant.
 

·
Registered
Joined
·
742 Posts
If you wouldn't mind... source?
Like asking for a source on "water is wet".

Do your own basic research, that is one of the first things you will come across.

And if you know so little about a topic, maybe stop pretending / believing you should act as if you know a lot? Dunning—Kruger affects us all. . .

Going down to dead flat is also instant-death, investment is gone.

And each of the dozens of LI chemistries has different characteristics.

LFP is the only one worth considering for House bank storage in a mobile context.
 

·
Registered
Joined
·
742 Posts
lithium ion batteries are ruined immediately if you charge when cold once.
Has anyone worded their claim that way?

LFP specifically is what is being discussed, not the dozens of other chemistries included in the LI umbrella.

Temperature of the core is relevant, not ambient.

Current rate is relevant.

But the statement

"LFP batts should not be charged when below freezing"

is not disputable.
 

·
Registered
Joined
·
13 Posts
'tesla' batteries:

https://www.batteryspace.com/prod-specs/NCR18650B.pdf

lots of LiFePO4 batteries: don't charge below 5 degrees C

Winston LiFeYPO4: allowed to charge from -45 degrees C
I have owned Winston batteries for years. They have performed flawlessly in Canada (i.e. cold) and I would not and have not charged them below 0. The Winston battery operators manual on pg 15 states continuous and instant charging 0/75ºC. I have seen brochures stating the low charging temperatures but they were probably a translation issue.

Charging below 0 will have a negative impact on the battery. The magnitude of the harm is almost certainly a function of temperature, duration and charge rate.
 

Attachments

·
Registered
Joined
·
495 Posts
As far as I know discharge in cold temps is not an issue, and most people charge as soon as they get home i.e. the pack is probably already warm from driving (discharge) and charging keeps it warm enough.

That said I have installed low-wattage reptile heaters on some of my racing packs (high discharges are easier at higher temps) and external heaters should be fairly easy to implement.
 
1 - 20 of 37 Posts
Top