Lithium battery charging

mackem10000000 · Aug 17, 2023

Morning people, I have acquired a 100 Ah lifepo4 battery and have question about fitting. I have a victron solar charger which will handle lithium, and plan to fit a dc-dc charger for engine charging. Question is what do I do with hookup charging. Can I just feed the output from the standard vw charger (above the fridge) into the dc-dc charger or would that be a problem....Any advice much appreciated (van is 2005 T5 2.5D california)

stim · Nov 1, 2023

Did you ever figure this out?

mackem10000000 · Nov 4, 2023

stim said:
Did you ever figure this out?

In the end I just rewired the factory fitted, hookup battery charger so that it changed the engine battery rather than the leisure battery. No problems so far.

stim · Nov 4, 2023

Ok thanks for the reply. So then you LiFePo4 only charges when driving via the DC-DC charger? I guess going from the factory AGM EHU charger into the DC-DC charger and then into the lithium battery does not work?

mackem10000000 · Nov 4, 2023

yes, that's basically what I did . I took the live from the EHU charger and ran it to the input of the DC-DC charger which is under passenger seat. Figured it was the same as engine battery positive and input are connected anyway

mackem10000000 · Nov 4, 2023

I set the DC-DC charger so it only charges when the input voltage is over 13.5 volt, which only happens when either engine is running or on EHU

stim · Nov 4, 2023

So you its not possible to have the output from the EHU AGM charger going into the input of the DC-DC charger so that the DC-DC charger then changes the charge profile and outputs correctly to charge the lithium leisure battery? Does it work to have a current coming in from the mains, through an AGM charger, then through a DC-DC charger and then to the battery?

Electronics is not my strong point FYI!

mackem10000000 · Nov 4, 2023

Do you also have the engine battery connected to the input of the Dc-Dc charger, or just the EHU charger.....I'm a bit unsure of just having the EHU charger connected. Can any of the experts out there offer any advice?

stim · Nov 4, 2023

Right now I just have the standard T6.1 Beach setup...75Ah AGM under the seat with EHU. I would like to change to a LiFePo4 and I think I have figured out the following:

DC-DC charger needs to replace the stock split charge relay to enable the correct lithium charge profile when the engine is running.
The Control panel of the T6.1 will not display the correct battery status and instead I will have to rely on the BT connection with the BMS of the battery. I have not found any info anywhere about how to get the display working properly.
The stock EHU charger probably only has an AGM charge profile (although I have not been able to confirm this) and so I would need to replace it or find a work around...

As far as I can find out, this EHU charger is hidden behind all the internal trim panels on the Beach model, so I am wondering if it is possible to go from the EHU charger into the DC-DC and then to the battery (I guess not).

I think the starter (engine) battery should be connected to the DC-DC input (hence DC to DC - it draws current from the starter battery to charge the leisure battery and then the alternator charges the starter) but then if you connect the EHU to this same terminal, does it charger the starter battery or does it act as an input into the DC-DC and thus charge the leisure battery (or break something)?

a892374923874 · Nov 5, 2023

The Victron dc-dc charger draws approx 30a from the starter battery or alternator. This cannot be reduced. The factory mains charger can only provide around 15a.

So if you connect the mains charger to the starter battery, the dc-dc charger will keep switching on and off as it discharges the starter battery into the lithium.

Kayleigh · Nov 5, 2023

stim said:
Right now I just have the standard T6.1 Beach setup...75Ah AGM under the seat with EHU. I would like to change to a LiFePo4 and I think I have figured out the following:

DC-DC charger needs to replace the stock split charge relay to enable the correct lithium charge profile when the engine is running.

The Control panel of the T6.1 will not display the correct battery status and instead I will have to rely on the BT connection with the BMS of the battery. I have not found any info anywhere about how to get the display working properly.

The stock EHU charger probably only has an AGM charge profile (although I have not been able to confirm this) and so I would need to replace it or find a work around...

As far as I can find out, this EHU charger is hidden behind all the internal trim panels on the Beach model, so I am wondering if it is possible to go from the EHU charger into the DC-DC and then to the battery (I guess not).

I think the starter (engine) battery should be connected to the DC-DC input (hence DC to DC - it draws current from the starter battery to charge the leisure battery and then the alternator charges the starter) but then if you connect the EHU to this same terminal, does it charger the starter battery or does it act as an input into the DC-DC and thus charge the leisure battery (or break something)?

You would like to, but have you worked out if you really need to?

It seems like an awful lot of expense to install a lithium battery. It depends on what you need to run and then it’s about right sizing the system.

This is something I have looked into myself for my T6 Beach in the past. I came to the conclusion that if I did need to upgrade the battery system I would install one of Roger’s solar panel kits with the optional 12v cable to charge my small lithium powerstation.

My 12v needs are a small fridge, router, laptop, lights, occasional use of the parking heater and mobile phone charging. I can last a couple of days (no hookup) using the existing leisure battery and powerstation without starting the engine. However, in practice I don’t tend to stay put that long, so both batteries can charge while I’m on the move.

Maybe you have already done all the analysis and determined that you really do need that expensive LiFePO4 solution, but if not I would encourage you to work out the right size system for your requirements first.

stim · Nov 5, 2023

I will be investing in solar first, 2 x 130W (ish) panels. When my stock AGM battery finally gives up (it is 2 years old now) I would prefer to replace it with a lithium one. This I'm sure will make me more or less self-sufficient in summer. The problem is, I ski a lot in the winter and can be staying in a car park for 3 nights (or more) in sub-zero temps with no power and snow covering any solar panels I have. I know from experience that with my fridge and charging my camera gear, the heater will already start to complain on the second night and definitely the third. A power station doesn't help me here because I cannot use that to power the heater and in any case, I would prefer not to have another big box to find space for.

A 100Ah lithium battery would give me 2.5 times the capacity I currently have (with less weight and greater longevity) plus the solar to help keep me autonomous without starting the engine.

If there is a way to have a power station feeding back into the leisure battery in a clean way (and I don't mean via the external EHU) to top that up to power the heater, I would revisit that as an option.

mackem10000000 · Nov 5, 2023

a892374923874 said:
The Victron dc-dc charger draws approx 30a from the starter battery or alternator. This cannot be reduced. The factory mains charger can only provide around 15a.

So if you connect the mains charger to the starter battery, the dc-dc charger will keep switching on and off as it discharges the starter battery into the lithium.

Are you sure that's correct a8?....My Victron DC-DC charger charges at a maximum of 18a. My T5 EHU charger can charge at up to 60a.