I certainly wouldn't have room to encase mine, though it does already have polystyrene insulation underneath
Fitting heat pads to LIFEPO4 battery
- Thread starter OllieGBR
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If you have a Victron BMV712, you can use the temp sensor and relay output on the back of the display.The Victron Solar MPTT will get information from the BVM-712 temperature sensor and will not charge if the temperature is below 5C.
However, the DC-DC charger is not able to limit charging based on temperature, (an oversight from Victron IMHO).
Therefore, even if you not using you leisure battery in the winter and it's still connected when you go for a drive, it will charge when the alternator has put enough juice back into the starter battery. It's this I'm trying to avoid by adding heat pads to keep the battery above 5C.
I'm back in the garage after a ridiculously busy week at work, so let's see how I get on today
I agree, it's hassle I'd not considered - however the pro's of Lithium still outweigh the con's.
You can use this output to control a larger relay, say 50A or 100A to disconnect the dc-dc charger feed from the battery.
You can disconnect either the dc-dc input side or the output side.
Heat pads will help in extreme cold..... it what the more expensive batteries have fitted internally, controlled via the bms normally.
From testing it seems that to generate any internal heat in a very cold lithium battery you need to draw a large load....
Running a few led lights won't help.
I've found you would need to run a coffee machine via inverter to generate some internal heat......or similar high current device.
I've seen another setup too where they used a 3rd seperatr smaller SLI battery to run the heat pads....
The battle born guys are saying that you CAN charge their Lifepo4 battery's bellow 0degc .... but it must be done at a very low charge rate......
Most spec sheets just say you can't charge below 0degc as a precaution.
The problem is how do you reduce the charge rate......?
It seems its easier just to disconnect the charge source till the temp rises enough.
Running a few led lights won't help.
I've found you would need to run a coffee machine via inverter to generate some internal heat......or similar high current device.
I've seen another setup too where they used a 3rd seperatr smaller SLI battery to run the heat pads....
The battle born guys are saying that you CAN charge their Lifepo4 battery's bellow 0degc .... but it must be done at a very low charge rate......
Most spec sheets just say you can't charge below 0degc as a precaution.
The problem is how do you reduce the charge rate......?
It seems its easier just to disconnect the charge source till the temp rises enough.
Yes. I ran some tests today. The aluminium plate hits 50C and took the battery from 5-9C in less than 5 minutes. Works better than I had anticipated. I also noted that the residual heat significantly delayed the cooling process.
Good idea - I will look to add some further insulation.
I will be adding a switch so that I’ll only activate it before using the van. It only gets used once per week during the winter.
P
Phil_G
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Sorry I hate to disagree but its bad to heavily load a very cold lithium battery Lee, self-heating at high DC currents through internal I²R losses within the battery is a Bad Thing
There have been self-heating experiments using alternate charge & discharge pulses, and using superimposed high frequency AC but I dont think its been applied to campervans yet 
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I already have temperature controlled relays disconnecting the charging sources, what would also be needed was some way of switching the heat pads on when a charge source was available and off when it wasn't. You don't want them heating up the battery every time it drops below temperature.
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That's an excellent result, thanks you've saved me a lot of experimentation
I'll get the same ones and hopefully I'll get the same resultsYes there's plenty of info out there saying you can actually charge lithium down to -20C, but as you say, the current has to reduce the lower you go and you would need something to manage that.
Yes I think it will have to be manual for now, I've got til next winter to come up with something better. Maybe with an audible alarm or light linked to a relay controlled ignition live to warn you to switch the heat pad off?
In fact the heat pads could be controlled by an ignition live relay and a temperature controlled relay in series so that both have to be active to switch the heat pads on (this is how I control low temperature cutoff to my Victron DCDC charger). That would take care of charging while driving, but automatic control of the heat pads for solar charging will take a bit more thought.
Drawing 45w from the battery will run it flat quickly.
3x 15w heat pads...
So running the pads fron IGN/engine run is a good idea.
Also maybe look at a timer option that maybe cycle ls the heat pads on and off... say 1mins on, 3mins off?.... so that they are not on all the time.
Saying that, seeing as we are looking to stop the charging below 0degc, this would imply that the have sufficient power from whatever source anyway... (solar, dc-dc, ehu) so that the battery will not be drained flat.
Any idea how quickly the heat pads raise the internal temp by 5degc?
3x 15w heat pads...
So running the pads fron IGN/engine run is a good idea.
Also maybe look at a timer option that maybe cycle ls the heat pads on and off... say 1mins on, 3mins off?.... so that they are not on all the time.
Saying that, seeing as we are looking to stop the charging below 0degc, this would imply that the have sufficient power from whatever source anyway... (solar, dc-dc, ehu) so that the battery will not be drained flat.
Any idea how quickly the heat pads raise the internal temp by 5degc?
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Also one thing to note ....
Your thermal couple shows 52degc on the alu plate.
That seems very warm, make sure that you are not over heating the cells in the bottom of the battery.
You need to check the temp parameters for the battery... 40,50, degc is normally the very maximum.
I think I would be happier looking at a plate temp below 30degc... may even 25degc?
I suppose it depends on how long the heating plate will be on for... or how often it cycles on/off.
Your thermal couple shows 52degc on the alu plate.
That seems very warm, make sure that you are not over heating the cells in the bottom of the battery.
You need to check the temp parameters for the battery... 40,50, degc is normally the very maximum.
I think I would be happier looking at a plate temp below 30degc... may even 25degc?
I suppose it depends on how long the heating plate will be on for... or how often it cycles on/off.
That looks like a lead acid battery in the top pic...?
What lithium are you going to use?
We can check the chsrge , discharge temp parameters.
That SLI battery would be full up of liquid electrolyte and have different thermal characteristics compared to a Lifepo4 full of 18650 or pouch cells... or even calb packs.
What lithium are you going to use?
We can check the chsrge , discharge temp parameters.
That SLI battery would be full up of liquid electrolyte and have different thermal characteristics compared to a Lifepo4 full of 18650 or pouch cells... or even calb packs.
Agreed on the power draw, however my van is rarely used and I will put in a manual switch to activate the temperature controlled heater when I’m going to use the van.
In my cold garage yesterday it only took a few minutes to raise the temperature 5C.
I’ll run some more specific tests when plumbed in.
fyi. . .
as an example the Valance max ambient temp is 45degC charge and 50degC discharge.
so i would keep the plate temp below that, say 35degc for a safety margin.
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as an example the Valance max ambient temp is 45degC charge and 50degC discharge.
so i would keep the plate temp below that, say 35degc for a safety margin.
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I was just using that for a test
After reading yours and Delmassive’s responses along with a sleepiness night, I can’t leave it at that. Good point regarding the high temperature and thanks for highlighting. I’m going to rip the whole lot back out again over the next few evenings and remove one of the heat pads. I’ll then run a more scientific test with timing and everything
That’s a shame Dean, I think you’ll find we’re seriously over complicating it ourselves because we’re tinkerers and like solving problems that for most people don’t matter or even exist.
Regardless of how you treat it, a lithium battery will significantly out perform any type of lead based battery.
The weight and power gains alone significantly outweigh the negatives.
As long as the infrastructure you add in now can cope with Lithium in the future, no harm in sticking with Lead and making the change when you’re comfortable!
Good luck!
Thanks Ollie
The biggest concern I have is this 5 degrees and below issue. I have a motorhome as well as my new T6.1 so I am slightly skewed in my thoughts, but.... I like to be “connected” to my vehicles. I travel extensively and like to know what’s going on. I have CCTV, temp, battery and various other monitoring systems connected via WiFi.
What I was hoping to do is stop having to be hooked up to the power the whole time and just keep the batteries topped up with solar. From dissecting the thread here, and another on a motorhome forum, it just seems like it is hassle. If we have a cold couple of days, then the battery can’t cope and all systems will be down.
I understand completely the benefit of the chemistry with regards charge/discharge/cycles/DOD which would be a benefit (weight not an issue), but this temp issue just makes it unworkable for me, I may as well just stay hooked up and kill my AGMs over time.
Thanks for everyone’s input.
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