LiFePo4 batteries in winter

[peterc10]

I have 2 x 120Ah lithiums supplied by KS Energy, which I fitted in the spring of this year. When we are not using the motorhome this winter my plan is to isolate my Lithium leisure batteries when not in use, but still trickle charge the lead acid cab battery via solar and/or EHU so that the Growler alarm and non-starter still works and the engine electronics still work. I envisage the longest period the motorhome will not be in use will be 3 months.

Is that sensible and what state of charge should I leave them at ?

My set up at the moment is

• An EBL29 that acts as a trickle charger to the cab battery and 12v distribution board. It does not charge my Lithiums because I have removed the 20A fuse.
• A Votronic 30A B2B
• 250W of solar panels via a Votronic MMP350 solar charger that charges the Lithiums and trickle charges the cab battery via the EBL
• A Victron IP22 charger for the Lithiums, which can easily be switched off.

All of those, and any other positive leads, are wired through a fused bus bar and then onto lithium batteries. I have a kill switch on the lead between the batteries and the bus bar and my intention is that I will just switch that off when I want to isolate the lithiums. Will all of this ensure that the cab battery will still be trickle charged enough by the solar charger, or should I also leave it plugged into the EHU so that the EBL will trickle charge it as well? I do not want another problem with my Airbag ECU because of low voltage. I am not sure what the residual current draw is on a Ducato, but I know that the radio and sat nav work off the leisure battery, not the cab. The only way that I know the state of the cab battery is by using the Hymer control panel, which needs the lithiums to be turned on as well.

 

[bigtwin]

Is it not possible to isolate the charge input via the LFP’s BMS? That would be the simplest method.

In terms of SoC for storage, around 50% should be fine.

Ian

 

[cyberyacht]

Given the potential for power cuts this winter, you might be glad of fully charged batteries.

 

[Reallyretired]

It should still charge your starter battery.
from your description as you are only isolating the lithium batteries. A meter will tell you if the starter battery is still being charged.
Lithium batteries seem to be best stored 50-60%

 

[peterc10]

Is it not possible to isolate the charge input via the LFP’s BMS? That would be the simplest method.

In terms of SoC for storage, around 50% should be fine.

Ian

The BMS does that automatically. BUT belt and braces are best, given the possible consequences.

As for SOC that has not dropped beyond 90% in the 6 months since I fitted them. Is there any reason why full charge is not OK

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[peterc10]

Given the potential for power cuts this winter, you might be glad of fully charged batteries.

Good point. We have already discussed using the motorhome as our escape pod.

But my main concern is ensuring the lithiums are not charged when they are too cold.

 

[cyberyacht]

Can your BMS not sort that out?

 

[Two on Tour]

But my main concern is ensuring the lithiums are not charged when they are too cold.

I sat our lithium battery on a thermostatically controller heat pad to stop the battery temperature from going below 6 degrees C.

 

[peterc10]

Can your BMS not sort that out?

See my post #5. Belt and braces is best at the price I paid for these batteries.

 

[peterc10]

I sat our lithium battery on a thermostatically controller heat pad to stop the battery temperature from going below 6 degrees C.

Thanks Paul. Our batteries are sat next to the Alde heating unit so there will be no problems with them getting cold when the motorhome is in use. If they dropped anywhere near to zero in those circumstances Angela would have already instructed me to turn the heating up or drive home PDQ.

Just seems wasteful of energy to heat the batteries up all the time throughout the winter when they are not in use. If we fancy a trip out at short notice we can switch the Alde heating on and the batteries would warm up quickly.

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[Two on Tour]

Just seems wasteful of energy to heat the batteries up all the time throughout the winter when they are not in use. If we fancy a trip out at short notice we can switch the Alde heating on and the batteries would warm up quickly.

I'm using solar energy that would otherwise be wasted, so no cost involved.

 

[peterc10]

I'm using solar energy that would otherwise be wasted, so no cost involved.

I can't see my 250W solars reliably running two heat pads throughout the UK winter. And to do that I would have to have the lithiums switched on, which would defeat the whole purpose of keeping them switched off when I am not using the motorhome.

 

[Two on Tour]

I can't see my 250W solars reliably running two heat pads throughout the UK winter. And to do that I would have to have the lithiums switched on, which would defeat the whole purpose of keeping them switched off when I am not using the motorhome.

My 410 watts of solar handles keeping my 280Ah lithium cosy through the winter months without breaking into a sweat.

My heat pads draw about 3 amps when on, but are of course not on all the time, so the solar holds it's own.
Sorry but I don't get this disconnecting your batteries, I don't see why, I just set the battery SOC lower over periods of non-use.

 

[bigtwin]

The BMS does that automatically. BUT belt and braces are best, given the possible consequences.

As for SOC that has not dropped beyond 90% in the 6 months since I fitted them. Is there any reason why full charge is not OK

I was suggesting that you, manually, disconnect the charge input via the BMS.

My understanding is that, unlike SLA, LFP batteries do not fare well if left fully charged and are, again unlike SLA, happiest when in a partial state of charge. The usual recommendation is to ensure that they are below 80% when it is expected that they will not be in use in the medium to long term.

But my main concern is ensuring the lithiums are not charged when they are too cold.

If you ’manually’ isolate the charge input via the BMS then this will not be a problem. I suspect that, by appearing to want double isolation, you are worrying unnecessarily.

Ian

 

[peterc10]

I was suggesting that you, manually, disconnect the charge input via the BMS.

My understanding is that, unlike SLA, LFP batteries do not fare well if left fully charged and are, again unlike SLA, happiest when in a partial state of charge. The usual recommendation is to ensure that they are below 80% when it is expected that they will not be in use in the medium to long term.



If you ’manually’ isolate the charge input via the BMS then this will not be a problem. I suspect that, by appearing to want double isolation, you are worrying unnecessarily.

Ian

The BMS is automatic. AFAIK the KS BMS is not changeable by the user. If it is I have not found out how

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[bigtwin]

The BMS is automatic. AFAIK the KS BMS is not changeable by the user. If it is I have not found out how

If your battery isn’t bluetooth enabled then that won’t be an option.

Ian

 

[peterc10]

If your battery isn’t bluetooth enabled then that won’t be an option.

Ian

Yes the battery is bluetooth enabled, but that is only to show what is happening with the battery in the way of SOC, voltage, current in or out etc. The bluetooth app does not allow the user to change any parameters set in the BMS

 

[bigtwin]

Yes the battery is bluetooth enabled, but that is only to show what is happening with the battery in the way of SOC, voltage, current in or out etc. The bluetooth app does not allow the user to change any parameters set in the BMS

Ahh, ok, that’s not viable then. When I’m leaving my batteries for any length of time I ensure they’re down to about 60% and then I switch of the charge input via the BMS.

Ian

 

[Pebble99]

The solar alone should top up the starter battery over winter. I'm going to insulate my KS energy underseat battery with Armaflex insulation especially underneath. Hopefully this will keep it well above freezing in the winter months when not used. I intend also to turn off the solar charging to the Lithium but don't plan to isolate it. As there is no load on the lithium since the EBL 20a fuse is removed, what is the benefit of isolating it ?

 

[bigtwin]

Hopefully this will keep it well above freezing in the winter months when not used. I intend also to turn off the solar charging to the Lithium but don't plan to isolate it.

If you intend to isolate the solar then there is no need to isolate the batteries. They are only sensitive to low temperatures when charging, they are perfectly happy to supply loads at temperatures below 0C.

Ian

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[peterc10]

As there is no load on the lithium since the EBL 20a fuse is removed, what is the benefit of isolating it ?

Because there will be load from the solars, which will be kept on in order to trickle charge the engine battery. I doubt that insulation alone will keep an unheated motorhome frost free throughout the winter. And I am not going to take the risk.

 

[DBK]

If you are disconnecting the leisure batteries I'm not sure how the solar controller will respond. Victron controllers will remember they are supposed to be 12 volts and not 24 volts but to work I'm fairly sure any controller will need a 12 volt supply.

You could just buy a cheap lead acid battery and connect that but it will need venting.

 

[peterc10]

If you are disconnecting the leisure batteries I'm not sure how the solar controller will respond. Victron controllers will remember they are supposed to be 12 volts and not 24 volts but to work I'm fairly sure any controller will need a 12 volt supply.

You could just buy a cheap lead acid battery and connect that but it will need venting.

It should because it is also connected to the cab battery to provide the trickle charge. That is done through the EBL's link to the cab battery via the 20A fuse on the cab battery. The alternative is to switch off the solar supply to the the solar controller and plug in the EHU to allow the EBL to trickle charge the engine battery.

 

[Raul]

You could try, but, I think DBK is right. If you disconnect the leisure ( primary) battery, the controller can’t see its connected to 12v. The second battery is a controlled load on controller, after the first is charged. It may not work on solar, only on secondary battery connected.
What you could do, is disconnect the lifepo4 from controller, and connect the starter as primary. That way will remain topped up.

 

[poppycamper]

I have 2 x 120Ah lithiums supplied by KS Energy, which I fitted in the spring of this year. When we are not using the motorhome this winter my plan is to isolate my Lithium leisure batteries when not in use, but still trickle charge the lead acid cab battery via solar and/or EHU so that the Growler alarm and non-starter still works and the engine electronics still work. I envisage the longest period the motorhome will not be in use will be 3 months.

Is that sensible and what state of charge should I leave them at ?

My set up at the moment is

• An EBL29 that acts as a trickle charger to the cab battery and 12v distribution board. It does not charge my Lithiums because I have removed the 20A fuse.
• A Votronic 30A B2B
• 250W of solar panels via a Votronic MMP350 solar charger that charges the Lithiums and trickle charges the cab battery via the EBL
• A Victron IP22 charger for the Lithiums, which can easily be switched off.

All of those, and any other positive leads, are wired through a fused bus bar and then onto lithium batteries. I have a kill switch on the lead between the batteries and the bus bar and my intention is that I will just switch that off when I want to isolate the lithiums. Will all of this ensure that the cab battery will still be trickle charged enough by the solar charger, or should I also leave it plugged into the EHU so that the EBL will trickle charge it as well? I do not want another problem with my Airbag ECU because of low voltage. I am not sure what the residual current draw is on a Ducato, but I know that the radio and sat nav work off the leisure battery, not the cab. The only way that I know the state of the cab battery is by using the Hymer control panel, which needs the lithiums to be turned on as well.

I also have 2 ×120 ah KS Energy batteries
And 200w solar via a votronic 250 duo charger...
My answer to your issue would be to isolate solar and EHU and fit a battery master to top up your starter battery from lithiums and then occasionally as lithium drops to about 30% turn solar or indeed EHU when temps allow. back on and recharge back up to 80%.

While here peterc10 could I please enquire how your Votronic 30A B2B is performing... I am thinking about fitting a B2B and that is the one I was looking at but noticed that 2 x 120AH (240Ah) was outwith the recommended size but still just within the max rate as stated by Votronic. Therefore I was contemplating the much larger and dearer 50A version.
Thanks.

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[peterc10]

While here peterc10 could I please enquire how your Votronic 30A B2B is performing... I am thinking about fitting a B2B and that is the one I was looking at but noticed that 2 x 120AH (240Ah) was outwith the recommended size but still just within the max rate as stated by Votronic. Therefore I was contemplating the much larger and dearer 50A version.
Thanks.

The B2B works fine. A steady 30A all the time until the batteries are full. Mind you we have had a good summer so the solars have done their bit as well. That means the batteries have never been below 90%.

 

[gerry mcg]

The Votronic 250 duo MPPT (and votronic 30A B2B) need a temperature sensor connected to the negative pole of the lithium battery in order to charge on the lithium. This significantly reduces the charging current to the lithium battery when temperature is below 0c

Good point. We have already discussed using the motorhome as our escape pod.

But my main concern is ensuring the lithiums are not charged when they are too cold.

Won't this achieve what you want?

 

[peterc10]

The Votronic 250 duo MPPT (and votronic 30A B2B) need a temperature sensor connected to the negative pole of the lithium battery in order to charge on the lithium. This significantly reduces the charging current to the lithium battery when temperature is below 0c


Won't this achieve what you want?
View attachment 684065View attachment 684066

I already have the temperature sensor fitted. It is the phrase "significantly reduces" that worries me, given that the advice of KS is that no charging should take place at or below zero. And this also assumes that the external temperature of the negative node will be replicated all through the battery, which I doubt. As I say I want to be sure that I do not damage my new battery bank which cost significantly more than a thousand pounds. I think that level of expenditure justifies my belt and braces policy.

I am coming to the conclusion that I will switch off the Victron IP22 mains charger (already done) and also switch off the solar feed to the Victron solar controller. I will also keep the EHU plugged in to let the EBL trickle charge the engine battery, thus keeping the Growler and non-starter working as well as the various ECUs. That leaves the only potential charging is from the B2B. I will therefore just need to remember to not start the engine until I am sure that the temperature is high enough.

The question then is do I leave the lithiums connected or not? Leaving them connected will mean that they will run down slowly with the residual demands of the Hymer's systems, and they may drop too much if I forget to check them. Disconnecting them is a more "fit and forget" option because their natural drain is low enough to not worry about. And I do not have any worries about starting the engine and the B2B kicking in. If I do disconnect the lithiums, I will need to remember to reconnect them before I switch back on the solar feed.

I am not recommending anybody else to adopt the same belt and braces attitude I have, but I started this thread to get some useful advice as to how I can achieve it, and I have certainly got some good ideas in this thread that gave me cause to think. For that I thank everybody who replied.

 

[poppycamper]

I am not recommending anybody else to adopt the same belt and braces attitude I have,

No I am a belt and braces sort as well, as stated KS Energy with solar fitted with temp sensor. Also looking to fit B2B with temp sensor.
However I would never rely on that alone and have a physical isolator on solar and will also have same when B2B is fitted.
My battery's never receive any charge unless warm enough to do so.

 

[Ingwe]

I am coming to the conclusion that I will switch off the Victron IP22 mains charger (already done) and also switch off the solar feed to the Victron solar controller. I will also keep the EHU plugged in to let the EBL trickle charge the engine battery, thus keeping the Growler and non-starter working as well as the various ECUs.

I have a fairly similar system (lithium batteries and Victron IP22 main charger). If you have switched off the IP22, is that not your EHU charger? On mine, they removed the fitted charger as it had no lithium profile. So now the IP22 is my hook up charger. So does the EBL have another mains charger? Sorry if I have not understood what you’re doing.

Also anxious about leaving my van plugged into EHU, I switched off the IP22 in the settings section and used EHU to power any 230v gear whilst using the van. But now it’s in storage indoors (so no solar) I just let the lithiums sit and hope the battery master keeps the cab battery topped up. Every two weeks or so, I go and check and if necessary plug in the IP22 for a couple of hours. So far, from full, the lowest the lithium State of charge after two weeks is 78%.

p.s. And I missed that you’d said all I’d misunderstood in your opening post! Note to self: read the whole thread.

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