Rockpool
LIFE MEMBER
Interesting video posted by Roamer batteries on self-heating lithium batteries.
Self-heated Lithium Batteries
- Thread starter Rockpool
- Start date
He states that self heating of LiFePO4 batteries doesn’t work. What he should have said was that it doesn’t work effectively on THAT battery.
The main reason for the 10°C thermal gradient, at the point charging started, existed was because the temperature sensor was mounted on the heating pad!
A no extra cost design change would be to mount the sensor between the two inner cell banks and that would restore the thermal gradient to normal ‘ambient’ levels.
Ian
The main reason for the 10°C thermal gradient, at the point charging started, existed was because the temperature sensor was mounted on the heating pad!
A no extra cost design change would be to mount the sensor between the two inner cell banks and that would restore the thermal gradient to normal ‘ambient’ levels.
Ian
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Rockpool
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Yes quite agree it’s all down to the location of the temp sensor within the battery.He states that self heating of LiFePO4 batteries doesn’t work. What he should have said was that it doesn’t work effectively on THAT battery.
The main reason for the 10°C thermal gradient, at the point charging started, existed was because the temperature sensor was mounted on the heating pad!
A no extra cost design change would be to mount the sensor between the two inner cell banks and that would restore the thermal gradient to normal ‘ambient’ levels.
Ian
I am just wondering where manufacturers with self heating pads locate their sensors?
But then again in the video they are freezing the hole battery, but you would expect in normal working conditions that the heating pads would probably kick in at around 3-5 Deg thus preventing the internals getting that cold?
Agreed, that’s probably not very representative of most installations.
Indeed, but only if there is a charging source present; the heaters are normally powered via the charging source and not from the battery itself.
Ian
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Two on Tour
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He mentions the chance of thermal runaway, .......... on a LifePO4 battery, really.
elliottkillingbeck
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He said at the end that self heating isnt a bad idea, but how its implemented at the moment is - I rekon thats a fair assessment.He states that self heating of LiFePO4 batteries doesn’t work. What he should have said was that it doesn’t work effectively on THAT battery.
The main reason for the 10°C thermal gradient, at the point charging started, existed was because the temperature sensor was mounted on the heating pad!
A no extra cost design change would be to mount the sensor between the two inner cell banks and that would restore the thermal gradient to normal ‘ambient’ levels.
Ian
elliottkillingbeck
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The heat pads are powered by incoming charge, they don't run to prevent it getting cold.
How it is implemented in THAT battery. He makes massive generalisations that are unwarranted.
Ian
elliottkillingbeck
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I'd look at other battery teardowns on youtube - most are very similar in terms of the heating at least.
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He may have lost some business over leaving heating out but he has also gained some too. I for one chose a Roamer battery because it didn’t have heating. The sellers of heated batteries will tell you about the advantages and the sellers of unheated batteries will tell you about the disadvantages. All sellers will try to convince you that their product is better, that is perfectly normal.
Mine is a Roamer 200Ah LITHIUM & I'm quite happy with it
My first lithium didn’t have heating. It was never a problem as I didn’t charge it when the battery was too cold. The battery was in the same compartment as the Truma heater.
That is the trick in my opinion. If the battery is in the heated living area and you don't charge when not in use....
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Agreed. either;
A heating pad at the base;
Or
A heating pad that wraps around the cells equally.
My choice is the former.
Then a centrally mounted temperature sensor between each cell (3 in total)
And that is the tricky bit. Most vans have permanently attached solar.
The lack of heating (from ambient or from pads) could start to interfere with your travel plans.
Ian
The lithium compatible Votronic solar controllers have a temp sensor so my system will only charge when the battery is above freezing. A heating duct runs past the battery so once the habitation heater is on the battery warms up ok.
Because I had read about too many problems with them. For instance some of the cheap ones use battery power to run the heaters, which is triggered by an incoming charge, this type can flatten the battery rather than charge it. Then there is the problems described in this video. I have been using unheated lithium for over 6 years and have not had any problems so it wasn’t a priority when buying for my new van.
The first self heated battery I heard of was the Relion LT which was introduced in early 2019 for use in remote monitoring equipment in cold climates. It used cylindrical cells which are easier to heat evenly. It is also expensive and a 100Ah one would cost more than I paid for my Roamer 230Ah under seat battery. Self heating can be done properly but it costs and done cheaply looks to me like a risky gimmick I can do without.
I bought fogstar last year, they come with self heating, although I bought them because I thought they offered the best value.
Charging is turned off below 5C, and during the winter I noticed on a couple of cold days that it was. You can turn charging off completely in the app if you want to, as I did.
No point in having the batteries heated when it's sitting outside our house plugged in.
Charging is turned off below 5C, and during the winter I noticed on a couple of cold days that it was. You can turn charging off completely in the app if you want to, as I did.
No point in having the batteries heated when it's sitting outside our house plugged in.
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Ours are cylindrical cell without heat pads, they are between the double floor under a bedroom locker, accessed via a hatch in the garage - when we're on the van, they have always been at or near ambient, and warm up further when charging.
All of the chargers switch off bellow 5°c, so in storage the batteries are protected.
Difficult to see how any "external" temp sensor can accurately measure the inside of the cells, so I'm happy to set conservative values, happily in winter storage the output from the 550w solar is pretty weak, so with the cells above 0°c there will be little or no damage.
Looking at the history of the last two winters, the batteries have never got bellow 3°c on the temp sensor (mild South Coast location), so I'm happy that any damage would be minimal, and I'll be selling up, or upgrading to some new technology well before they expire.
I wouldn't have solar connected all the time with a lithium. They don't like being stored fully charged.
Indeed, but if you’re not using it then you’d switch off the charge port via the BMS.
However, in use, most folks would have the solar permanently connected unless they keep a weather eye on the weather for extremely low temperatures.
Ian
I think there maybe two issues there - One is that in storage ie fully disconnected there's no advantage in storing the battery at high SOC levels since the self discharge is only 2%ish, so over 6 months a battery stored at 60% is going to be fine. Charging them correctly after the storage period will then presumably cell balance them correctly for the next season. What I've never seen explained clearly is what happens to a battery stored at 100% that doesn't happen at 90% or 80% or 50%, so I've kind of consigned that "don't store at 100%" to the myths and legends file, and in the past mine were left as they were.
The other is that leaving them attached to a charge source albeit on a trickle charge can lead to problems if there is some small leakage past the BMS into some cells where one or more can be overcharged/damaged. I'm not clear on how that happens but am familiar with one set of expensive large batteries where the manufacturers guidance said it was fine to leave their charger switched on maintaining their batteries over the winter, and when the batts were found to be duff the following spring gave the response that one cell in each battery had failed, and then the "leakage" bit came up.
In our van there is always some cycling going on, around 2-3% of capacity, due to the victron kit, small CBE monitoring functions and the Ablemail topping up the starter battery. The solar chargers go on and off everyday, and are crap in deepest winter, so the battery can get down to 65%SOC if left (couldn't drive it much last year over winter due to hips), is that storage?
Fogstar have responded on a facebook post about this;
So in a battery with 4 cells. They place a heating pad between 1 and 2, a temperature sensor between 2 and 3 and another heating pad between 3 and 4.
This seems to me to be optimal as each heating pad will heat the cells on either side and the centrally mounted temperature sensor is optimal for entire battery temp.
Here is a large version of the image so you can see the orange tabs better. This is an 8 cell battery so 24V.
I really do like the way they have done this. Well done Fogstar.
So in a battery with 4 cells. They place a heating pad between 1 and 2, a temperature sensor between 2 and 3 and another heating pad between 3 and 4.
This seems to me to be optimal as each heating pad will heat the cells on either side and the centrally mounted temperature sensor is optimal for entire battery temp.
Here is a large version of the image so you can see the orange tabs better. This is an 8 cell battery so 24V.
I really do like the way they have done this. Well done Fogstar.
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Agreed and as I said in my initial response, the weaknesses highlighted by Roamer applied to that specific battery/brand and was easily resolvable by simple design changes.
They did themselves no favours with that video and, in fact, undermined their credibility.
Ian
Not sure you could do a lot better than that without building them into the cell itself.
Looks like a 12V battery to me. The cells are doubled up, I think.
You are correct. I just saw 8 cells and assumed without looking at how they were connected. My mistake and well spotted
I'm not sure either, but I think it's to do with the inaccuracy in the measurement, and the fact that lithiums really do not like being over-charged, unlike lead-acids. If you are charging to a measured "100%" then that's probably say 97% to 103% in fact. So a 50-50 chance of overcharging. If it was limited to 90%, or even 95%, that danger would be averted.
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