Use vehicle generation system to charge leisure batteries, replace with B2B charger retaining the existing wiring, or replace everything?

[bofhchaos]

Hi all,

I'm in the UK. I purchased a VW Crafter van and intend to convert it into a campervan. I'm currently stripping it of the original racking and equipment fitted by the previous company. One piece of equipment the previous company fitted was a generation system with a secondary alternator on the engine connected to an inverter that can supply 110v, 24v, 12v or DC for welding. The system can supply up to 150 amps, is large, and weighs 26kg. I'm considering my options on what to do with this. I think I can use this system to charge the leisure batteries. However, I expect that it can't charge Lithium iron phosphate batteries. I can't use the 110v, 24v and DC welding outputs. I believe my options are:

1) Use the system to charge the leisure batteries. This is the cheapest and easiest option, but it takes up a lot of space, and I may be unable to use LiFePo batteries.
2) Remove and replace the charger with a B2B battery charger while retaining the secondary alternator and wiring. The new B2B will take power from the secondary alternator and charge the leisure batteries. However, I don't know if the B2B charger can cope with being connected directly to the alternator, if it can take the current from the alternator, or if I can use an A2B charger. The advantage is that I don't have to do much re-wiring, the B2B charger is significantly smaller, and I can use LiFePo batteries. However, it will cost money.
3) Rip everything out, including the wiring, except for the secondary alternator, leave it free-spinning, and use the B2B charger connected to the starter battery as designed. It is the safest option but costs the most in terms of time and money.

This page shows the power system I've got installed in the van - AutoMate - Onboard Power Systems - Motor On Services - https://www.motoronservices.co.uk/services/automate-onboard-power-systems & page 6 of their brochure - https://www.motoronservices.co.uk/_webedit/uploaded-files/All Files/Motoron services brochure.pdf
This page shows an example B2B charger - Victron Orion XS 12/12-50A DC-DC battery charger - https://www.simplysplitcharge.co.uk/products/victron-orion-xs-12-12-50a-dc-dc-battery-charger

I would appreciate any advice you could give. Thank you. Best regards.

 

[James]

You should be able to get a good size 110v battery charger off the shelf.

 

[happysteve]

It might be worth checking the specs of your intended LiFePo battery, as these all have built-in battery management units in them, and most will just accept whatever charging voltage (and offered current) is available and deal with it appropriately. My friend with a 2016 Sprinter had a B2B system connected to the factory-fitted starter battery and standard alternator, previously charging 3x lead acid or AGM batteries, which he changed for a big Li battery. Although the B2B controller has lots of different options for the type of battery it will charge (including LiFePo), the manual for the Li battery stated we should just use the standard lead acid settings, and basically the built-in battery management would decide the best way to charge the cells. This was the same for the solar panel DC-DC inverter

Your mileage may vary, of course.

I suspect it's not a good idea to connect a B2B system directly to an alternator without a (source) battery being in there as well... it may work, but it's probably not spec'ed for it.

Given that you've already got this monster alternator installed already, if it works and has a useable output that your intended lithium battery will be able to use, that might be the way to go - but you'd need the specs of both the alternator and the lithium battery.

 

[happysteve]

I would also caution against having a free-spinning alternator that's not connected to anything.

If you can remove it altogether, you will gain 26kg of weight capacity. This is less of an issue once the van is re-classified as a motorhome, but until then I suspect with all the fitting out, you're going to be pushing the weight limit of the vehicle anyway.

 

[bofhchaos]

You should be able to get a good size 110v battery charger off the shelf.

I don't want 110v. I'm just saying it's what the existing charger can do.

I suspect it's not a good idea to connect a B2B system directly to an alternator without a (source) battery being in there as well... it may work, but it's probably not spec'ed for it.

Given that you've already got this monster alternator installed already, if it works and has a useable output that your intended lithium battery will be able to use, that might be the way to go - but you'd need the specs of both the alternator and the lithium battery. I would also caution against having a free-spinning alternator that's not connected to anything.

If you can remove it altogether, you will gain 26kg of weight capacity. This is less of an issue once the van is re-classified as a motorhome, but until then I suspect with all the fitting out, you're going to be pushing the weight limit of the vehicle anyway.

Maybe I should install a tiny lead-acid battery and use the proper campervan B2B charger to charge the LiFePo batteries so that I can use the monster alternator? I.e., Alternator -> tiny lead acid -> B2B charger -> LiFePo batteries?

If so, what's the smallest lead acid battery size I can get away with? Should the B2B charger be rated at 150 amps, or can I go for a lower rating, like 50 amps?

Thank you so much for your time!

 

[happysteve]

I don't want 110v. I'm just saying it's what the existing charger can do.



Maybe I should install a tiny lead-acid battery and use the proper campervan B2B charger to charge the LiFePo batteries so that I can use the monster alternator? I.e., Alternator -> tiny lead acid -> B2B charger -> LiFePo batteries?

If so, what's the smallest lead acid battery size I can get away with? Should the B2B charger be rated at 150 amps, or can I go for a lower rating, like 50 amps?

Thank you so much for your time!

Depending on the specific battery you (intend to) buy, you might be able to just do Monster alternator -> LiFePo4 battery. The BMS for the fancy battery might let you set ot limit the maximum charge current, so (for example) your alternator doesn't overheat if you're using it while idling (the risk is the alternator fan can't cool it down enough at low RPM).. but if it's a monster alternator, it's probably not going to be an issue anyway.

Regarding the spec of a B2B system, it depends on what the capacity of your alternator is, and the capacity (AHr) of your battery / batteries is. It also depends on your usage - are you living in it, constantly moving around etc... do you need to maximise charging because you won't be running the engine much, or is it more likely you'll do a long journey, then stay still for a max of 2 days and there's no risk of your battery running down in that time?

My gut instinct says having an imbalanced system - where the alternator can do, say, 100A @ 13V, the B2B can potentiually do 150A, and the LiFePo4 battery can take whatever you throw at it (as long as it's not too hot or cold), and only a tiny lead acid battery to sort of regulate things... my gut just says that little battery's not going to last long.

I stress this is not my area of expertise - I've only worked on one van conversion project, as a favour for a mate, and he did most of the research and decided what to buy, I just helped him wire it up safely. What I would say, is that moving from AGM batteries to lithium was transformational, and genuinely life-changing for my mate who lives in his van, particularly in winter when there's not as much power from the solar panels. Amazing technology.