Upgrading 12V system - equipment choices and compromises

[fred_jb]

I have just completed a major upgrade of our van's 12V system. The van was new in August 23 and is an Etrusco CV540 DB, with Etrusco being part of the Hymer group and as such the electrical spec was fairly basic, with a Schaudt Electroblock EBL 31 managing the power distribution, though due to the Euro 6 alternator the system did include a Schaudt B2B, but no solar. We have done several 3-4 week trips so far this year and have started to notice that without a hookup the batteries get depleted fairly quickly and didn't seem to charge very quickly while driving. We use a Starlink quite a lot in the evenings and have a compressor fridge, plus an electric travel kettle which we find convenient. I had fitted a 1000W Renogy inverter so that we could use the kettle off grid. I also fitted a couple of solar panels early in our ownership, giving a total of 280W with a 20A Renogy MPPT controller.

Following the latest trip I decided to overhaul the system with a 300Ah Lithium battery from Fogstar and a matching Fogstar mains charger. I went with Fogstar for this due to their good reputation on the forum and competitive pricing and choose the Fogstar Drift for the built in Bluetooth and heater. I decided to also replace the Schaudt B2B and Renogy solar controller with a combined B2B/MPPT unit from Renogy as I have been happy with the Renogy kit and find it is competitively priced. I wanted a B2B which could be managed by an app, a facility which the Schaudt unit lacks. I also added a Renogy shunt as although the battery does have Bluetooth connectivity I wanted to get as much info as possible in one app and this lets me see battery charge and power use in the same app used to manage the B2B/MPPT controller. I upgraded the inverter to the 3000W model as we have found taking a small air fryer with us has been a bit of a game changer and wanted to be able to run it off grid which the 1000W unit was not powerful enough for. I am also intending to fit the Renogy Core One display panel which was another reason for sticking with one make. This can display all the same info as the Renogy app, with the addition of a van levelling sensor display, which can also be replicated in the phone app, and could be very useful.

So that is the reasoning behind my choices. It has been a big job, not least due to ripping out some of the converter's inadequate and badly routed cabling, but I finally got everything up and running this afternoon. I then spent some time tidying up the remaining converter's rats nest of wiring and putting right some collateral damage where my delving into the innards had dislodged a couple of wires which had stopped the step and a couple of lights from working! The battery, as someone helpfully reported on here fits snugly under the drivers seat in place of the two AGM batteries, leaving space for the shunt and 300A fuse feeding the inverter. The inverter, B2B/MPPT and mains charger have been fitted inside the dinette seat joined to the battery via a metre or so of hefty 375A cable. The inverter terminals act as connection busbars for the other equipment, including the Starlink DC POE based power system. I've included a few pictures below.

So far I am mostly happy with the system apart from the excessively noisy fan in the Fogstar mains charger. I suppose the main compromise has been to stay mainly with one manufacturer for the sake of integated reporting, rather than selecting best of breed from several manufacturers. Though Renogy may not be regarded as top tier, their prices are reasonable and I have had no complaints with performance. I have been particularly impressed with the Renogy shunt. After telling it the capacity of the battery and the current SoC as reported by the Fogstar app I told it to sync, and it has since reported virtually identical figures to the Fogstar battery app. This is just as well as I find the Fogstar app annoying to use as every time I open the app it seems to take an age to locate the battery and often fails to do so and starts a Bluetooth search listing a plethora of irrelevant devices before eventually finding the battery. Thankfully I won't need to use it much in future as I can get most of the same info from the shunt.

 

[LithiumConvert]

Your 300A fuse may not sit well with the 250A maximum continuous power draw from the Fogstar battery.

Personally, I would have put a low value fuse in the thin red positive supply wire to the shunt - alkthough if anything serious does go wrong with the shunt that wire will make a good fuse.

I find the 20A charger built into the EBL is very quiet and quite adequate because if we are on EHU it will invariably be overnight - 15 hours or more.

 

[fred_jb]

Your 300A fuse may not sit well with the 250A maximum continuous power draw from the Fogstar battery.

Personally, I would have put a low value fuse in the thin red positive supply wire to the shunt - alkthough if anything serious does go wrong with the shunt that wire will make a good fuse.

I find the 20A charger built into the EBL is very quiet and quite adequate because if we are on EHU it will invariably be overnight - 15 hours or more.

I have been considering changing the fuse to closer match the battery. Renogy suggest a 400A fuse for the 3k inverter! However I don't want a fuse that will immediately blow if I ever draw what is an allowable current of 250A, i.e. the maximum output from the battery, so it is difficult to determine what value to choose. If 250A is the max sustained output from the battery then that implies that an overload will momentarily go higher than 250A before being limited by the BMS, and that is when I would want a fuse to blow which is why I chose 300A. What value would you suggest, maybe 275A?

Renogy do not suggest fusing the battery voltage sense wire and I presume this is a high impedance input which is extremely unlikely to develop the sort of fault which would draw a lot of current, so I am fairly relaxed about that, and as you say it is a thin wire which would not survive a large current anyway.

I agree that the EBL charger is entirely unobtrusive, but it does not have a lithium profile and I thought that continuing to use it might affect the warranty of my expensive battery! The Fogstar 50A charger is not so expensive so I may risk it's warranty by replacing the fan at some point!

 

[Kannon Fodda]

The fuse needs to match the rating of the cable. Calculators online will show you the max current allowable for the cable cross section and length (double to allow pos and neg wires).

But 3000W at 12V is 250A so just on limit of your lithium battery output rating. Your 300A fuse allows a tad overhead on the startup short term load, if the cable can cope with that.