Revamping van electrics - looking for advice

[trotski94]

This is probably going to be a bit of a dump of information and questions, as I've been periodically looking in to this over the years.

I have a 2004 autotrail fitted with a Sargent PSU2005. This thing already annoys me, since twice now I've had failures of fairly bog standard parts that they have made a pain to replace by riveting the case shut (the little red "charger" switch stuck shut, so replaced like for like, and I had the main RCD fail so again replaced like for like). I've taken to replacing the rivets with rivet-nuts and screwing the case shut to make like easier, but I digress.

Unsurprisingly the box is just a combination of RCD & MCBs on a standard DIN rail, a bog standard looking no-name 12v PSU, and a couple of fuse holders all neatly wired in. At some point I would like to upgrade from a standard AGM leisure battery to a lithium one and replace the dead solar panel I bought the van with with ~400W of solar (I'm currently lucky if I see 30w), but I'm not sure how to integrate it with the existing 12v system.

Pretty much all of my uncertainty hinges around the batteries - I have a background in household electrics and have done plenty of work on 12v automotive stuff so that I'm all comfortable with replacing, but I'm not sure how it all works with the battery especially when it comes to replacing the charging system (which is currently just a standard 12v PSU, thats got to be pants right? I fitted a shunt to the battery alongside an inverter and I know I get piss poor charge rates when on mains so assume this is the reason why)

First proper question - far as I understand it 12v lead-acid-based leisure batteries are only good for safely (i.e without damage) discharging down to about 50% of their rated capacity, rendering my 100Ah battery effectively 50Ah in use. Do I understand that correctly? I can go to 80% discharge without truly damaging the battery, but it significantly reduces possible charge-discharge cycle count right?

Second question - AGM can only be charged at a rate of 25~30% of its capacity, right? Meaning again, with my 100Ah 12v AGM I can only charge at around 12v 25~30a max? If thats the case, I definitely need to do one of: a) Downgrade my solar ambitions to ~300w, even if that means over-spec'ing the panels and limiting at the charge controller, b) add a second AGM battery in parrallel or c) do the lithium swap

Charging a lithium battery - if I do the lithium swap, how does that work for charging the battery whilst also using the 12v systems on the van? This is the part I know the least about, so am at most risk of over-engineering a convoluted solution

Besides from installing the inverter, the van wiring is exactly how I bought it, but it does have what I assume to be a non-stock solar system fitted - Basically right now when we are on mains, both the solar charge controller and the 12v PSU both supply current to the 12v system. This both runs everything 12v (lights, fan, etc) and charges the AGM battery. From previous experience I know lithium batteries require special charge controllers, so at best this system will not properly pump any significant charge into the battery and - correct me if I'm wrong - at worst will be dangerous. During normal operation, even when charging, we can be drawing anywhere from ~50w to ~200w running the inverter, lights, fan etc.

1. If using lithium, would the battery need to be isolated from the 12v system during charge from mains? If so that would mean I would need a separate 240v AC => 12v DC PSU to power the vans electrics during mains charging, is this normally how its handeled?
2. How does the above work when charging from solar? Does the battery also need to be isolated from the vans 12v system for the charge controller to properly do its thing, or would I be able to run a load (mostly the inverter, its a 1200W inverter but at most I tend to draw 100~200w from it in a typical situation) whilst the solar charge controller does its thing? If the battery does need to somehow be isolated, is there any way to run the 12v system whilst also charging the lithium from solar?
3. Do I need to install a DC-DC charger to charge the lithium from the alternator when driving? Assume this is a yes
   

 

[Bessy765]

One of the things often overlooked is the wiring as you are considering Lithium heavier potential currents may occur make sure the wiring is up to it. You need ideally a mains charger with a lithium profile to get the most from them. We have 700 watts of solar 2 x 100 amp Lithium batteries and a Victron 12/2000/80 inverter/charger. No special requirements for us when using this system. We do not have a B2B as our installer stated it was not necessary, although this is often debated on this forum. He warrants the installation for 5 years and our Transporter batteries for 10.

 

[trotski94]

Yeah understand that - I expect to have to do fresh runs of anything carrying charge current, so mains charger, B2B charge all way back to main starter battery, and the solar controller (currently the solar controller just piggy backs into a random part of the stock 12v harness close to the roof, which always felt a bit dodgy to me, but I did the math on the max amperage and copper cross section and the stock cable to my surprise was good for it, but would be happy to fix that properly)

Does the Victron unit also handle charging from shore power? If so could be tempted to shell out and replace the current inverter with a full unit like that, current one I fitted is just a relatively cheap Chinese piece

 

[trotski94]

Do the charger/inverters also take in solar, or do you still need a seperate solar controller?

 

[Bessy765]

My Victron handle the ehu input has adjustable input so if you are on a campsite with a low amperage supply you can set it to the supply say 6 amps and the inverter will make up the shortfall

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[Headrush]

Just FYI, the charger switch on the Sargent unit comes out from the outside. Just use a screwdriver to lift a narrow edge and push in slightly to release the clip. The wires are long enough to allow you to easily swap it over.
Been there, done that.

 

[CAB96]

Welcome to the forum.

I'm no expert, I suggest you spend some time looking through the many electric threads on here.

1+2. No need to isolate, leisure Batteries can be charged and supply charge at the same time.

3. Most on here will say yes, in order to protect the alternator.

 

[Cush]

Welcome. You could look at going hybrid where you can keep your charging equipment and upgrade as you go along. You won’t charge at optimal but it will do a bit of charging. I would upgrade the solar first. That keeps my lithium topped. And will be transferable to the lithium as most controllers have a lithium profile. If you are off grid in winter then b2b will keep you charged. Lead acid will “protect” your alternator from the lithium disconnecting ( so might a lead starter battery but still researching that).

 

[autorouter]

Does the Victron unit also handle charging from shore power? If so could be tempted to shell out and replace the current inverter with a full unit like that, current one I fitted is just a relatively cheap Chinese piece

The Victron Multiplus inverter/charger is much better than having a separate inverter and charger. It does several things the separates can't do. First, it sychronises the inverter mains waveform with the incoming hookup waveform.Then it can add power to a weak mains hookup. So with a 6A hookup post, it will limit the power taken from the hookup to 6A. It can use that 6A, adding extra power from the inverter when necessary. When the load reduces, it will automatically charge up the batteries again ready for next time.

If you are very rarely on hookup, then you won't see much advantage over separate inverter and charger, but if like me you often go on Aires with 6A hookup it's great.

Do the charger/inverters also take in solar, or do you still need a seperate solar controller?

Actually, Victron do a unit called EasySolar which is an inverter/charger with a built-in solar controller. But they aren't very popular for motorhomes, people seem to prefer the separate MPPT controllers. All their stuff can be coordinated using Bluetooth and other connections, so having them in one box isn't necessary to build up a fully coordinated system.

 

[autorouter]

Second question - AGM can only be charged at a rate of 25~30% of its capacity, right? Meaning again, with my 100Ah 12v AGM I can only charge at around 12v 25~30a max? If thats the case, I definitely need to do one of: a) Downgrade my solar ambitions to ~300w, even if that means over-spec'ing the panels and limiting at the charge controller, b) add a second AGM battery in parrallel or c) do the lithium swap

One of the most popular upgrades is to add a second leisure battery in parallel with the existing battery, to double the charge storage. It's often the first upgrade that is done., even before adding solar. I should warn you that AGMs are not popular with many on here, and they prefer Gel batteries. AGMs need to be properly charged with the correct charging profile, or they will have a very limited life. However I think Gels are particularly sensitive to high charge and discharge amps, so be careful if you are thinking about a high power inverter.

If you go for lithium, you need to know that lithiums should never be charged if the temperature is below zero degrees. Many lithium chargers have a temperature sensor, and cut off the charging at freezing temperatures, while still allowing discharge - to run the heating for example.