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Motorhome advice? 1600-2400W 24V system, BMS, multi-MPPT for shade

My bus has a 24V alternator / starter setup. Seeking advice on a 24V leisure/office setup, as well.

I'm new to this. Does this setup make sense?

Panels: 4-6x 410W 24V / 49.5V Voc, 9.76A Imp each, used in PAIRS

Batteries:

  • 2s2p LiFePO4 180Ah (total 600Ah effective to 80% DoD)

...OR...

  • 2s4p AGM 200Ah (total 600Ah effective to 50% DoD)

Controllers:

  • 3x Victron SmartSolar 100/20s (3x = top, left, right of vehicle) MPPT-synced with new 1.49 / May update(?) to adapt to partial shade
  • 1x BMV-712
  • 1x BMS-12/200? Needed if each 12V 200Ah battery already has a cheap BMS built-in
  • Something that can charge the 24V starter batteries as well? Recommend?


MPPT - Solar Charge ControllerBMSBattery Balancer
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Michael Riley answered ·

@Nick Wiggill. Nick, see you have had no takers - this can be frustrating. I can only say that each installation comes from a whole heap of previous experiences, knowledge and preferences. I will only make the following comments based on my experiences and preferences and yours are possibly different. Our system is used on a sailing catamaran on the East Coast of Australia.

a. System voltage. 48 V house has better 'power density' than 24 V and it is likely to be an issue of what 'consumers' you have; want to have and the $'s you want to spend. i.e. 24 V LED's are common; 48 V less so. Therefore additional componentry or equipment etc. I have moved from 12V to 24V Lithium.

b. Battery Type. If you intend to have high current demands (i.e. cooking with microwave, induction cooker; like to use electric jug or want to reduce reliance on gas - then Lithium is the way to go. If you can limit your current demand - which is based almost entirely on trying to extend the life of your LA (AGM) then you have the option.

c. Charging. Remember that whatever you take out you have to put back in so there is no need to have Lithium and draw down SOC if you have no easy way to put it back in.

d. Solar. I use 65V panels. This voltage does not pose an electrical hazard when on the roof etc; the transmission loss from panel to MPPT is reduced and have installed very healthy sized cables to ensure that I minimise this loss. i.e. I have spent a lot of money to harvest solar and do not want to lose it to heat or transmission losses. Also have placed the MPPT right next door (not above) the battery stowage. You state in 'pairs' but not whether in series or parallel? I wired each directly to the a fuse box so that I can isolate input from any panel or 'the big red switch' to isolate all panels. This is located within a few mm of the MPPT.

e. My SmartSolar MPPT has all three (3) panels connected directly into it (i.e. one controller). I have a generator so do not want another MPPT just for redundancy. If often get near maximum yield (i.e 1 kVA from 3x340 panels) There is always some shading on a sailing catamaran but the controller maximises yield. It is 'blue-tooth enabled out of the box.

f. Battery Life. My understanding/research indicates that I maximise AGM life by not going below 60% SOC (really is a voltage) and NEVER using high current draws. LA (Lead Acid) loves being fully charged and never deep discharged.

Maximise LIPO life by never leaving fully charged; ie. regularly operate with partial charges (opposite of LA) say between 95%-35% can over double the typical life; can handle high discharges but you have a 'charging' conundrum in that you need to put back in what you have taken out - this means from a system point of view you need to also look at your charging regime - particularly if relying on solar.

LA (AGM) is particularly suited to Solar charge because to get 100% full you need to run on 'FLOAT' for significant period of time - solar can do this without to much 'management' hassle. If charging LiPO you are likely to be running a generator and this does not like 'float' so you need to put it in quickly - bigger charger; less time etc.

712 BMV. Good management device. Can read from iPad/Tablet via Bluetooth out of the box. Victron Connect seems to provide good collection.

Charger. There are several 'smart' chargers with 1 x 2 or 3 outputs for this exact reason. If you are going 'LiPO' then there is a lot of 'management' that comes with it and being all one brand and all 'connected' has some distinct advantages in this case. If you use LIPO then also may want to go the whole way and get a VenusGX or similar.

No inverter mentioned but you mention 'office' - is there no 240VAC requirement. If not therefore not sure why you would want LiPO as in the end whatever AH you have you need to put it back in and this can be more expensive (bigger charger, more management o'head etc) with LiPO. If you want 240VAC then a MultiPlus or equivalent will solve the charging needs for both house and 2ndry charge for start.

Management systems, remote control and monitoring etc comes down to a lifestyle and 'gadget' type of thing. If find that the Victron componentry from one end of the scale (simple) to the other (fully featured).

Hope I read your intent correctly. Best of luck

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Hi Michael. Thanks so much for this. A few remarks in reply, though you have basically confirmed the setup and I appreciate that...

Yes office + mobile home- 220V for laptops mainly. Not keen on gas or shore power hence high capacity panels and high draw-capable batteries for use of tools e.g. table saw at 1500W peak run for 30 secs at a time, drills/Dremel, jigsaw, 1500W small induction plates, kettles etc over short periods. Each of these high draw appliances will run one at a time, with the exception of anything else simultaneously except basic LED lighting and small parasitic draw. 3kVA inverter should do nicely; 5kVA to future proof against aircon running in background as well.

LiFePO4 8.6kWh @ 24V is now the deal - order placed today. Cells come with own BMS for series balancing of parallel sets within greater, single battery. Enough to go 2-3 days on low usage of about 2.5-3kWh / day. 24V is safe enough to work with and matches vehicle alternator / starter batteries so total win on that front. Re LiFePO4 life reduction on 100% charge - I will need to electronically limit this - thanks. Another reason to go Victron!

1600W total panels here... agree with paying for decent cabling to reduce loss... never mind for long-term safety under the elements. High quality copper cables + properly rated fuses through the system.