Sample System Design for a large mobile system.

[FilterGuy]

Hi folks,
I designed this system for someone and I thought I would put it here for others to comment on and/or use. (It is intended to go on a full-sized Schoolie)



One aspect to be aware of is that the DC loads have no low voltage disconnect. The only line of defense is the BMS in the batteries.
The solar panels are a bit underpowered for the size of the system, but it is all that can fit in the available space.

 

[OffGridInTheCity]

1) Maybe an overall battery on/off? or are you planning on using the individual EG4 circuit breakers?

2) I added a rotary switch to my system so I could direct shore power directly to the AC Distribution box for long term storage. See *3 as part of this. This switch let's me turn off the MPP + Battery to avoid using them/excess wear and just sit at home connected to grid for long term storage.


Just to share, nothing fantastic....
3) I went with a 120v -> 12v @ 80a transformer so the 12v power is part of the AC distribution - see #2 & #4. I don't think the losses of 120vac -> 12vdc are significant.

4) Added visible meters showing power flowing thru the AC distribution panel - this is really useful as one can turn on the mini-split + instant hot water at sink + 5gal water tank for showering + hot plate + microwave + k-cup all at once and the power really adds up fast! Good to be able to monitor.

5) I added a 30a Go-Power ATS between shore and MPP so I can have my on-board generator hooked up all the time and, if I forget it will auto-switch to generator and back to grid. OK - it could be overkill

 

[rmaddy]

Nice system.

A note about the 48->12V DC converter. The 30A would be the 12V output. So I would estimate the 48V input will only be 8 or 9A.

Something like a Victron battery protect could help deal with low voltage caused by the DC loads. Put it between the DC disconnect switch and the DC converter. Actually, it could replace the DC disconnect switch since the battery protect can be turned on and off like a switch.

Maybe consider a 35A dual-pole AC breaker between the shore power plug and the MPP. That could help protect the MPP from bad campsite wiring.

 

[RandyP]

Hi folks,
I designed this system for someone and I thought I would put it here for others to comment on and/or use. (It is intended to go on a full-sized Schoolie)
................

Is using the Chassis ground for both sides of the Sterling 12-48v charger the best wiring configuration for that device? I know its a three wire device, common ground device.

 

[FilterGuy]

Is using the Chassis ground for both sides of the Sterling 12-48v charger the best wiring configuration for that device? I know its a three wire device, common ground device.

That is something I debated with myself on. It turns out they decided not to use the alternator charging because it cost too much so I never got to the point of a final decision. (I could not find a reasonably priced 12V-48V charger that looked reliable enough to trust...Suggestions welcome)

Since the high current side is the 12V side I was going to advise putting the sterling closer to the engine compartment and making the lower current side the long part of the run to the battery. (One thing that is really nice about the sterling is it has a voltage sense line that allows it to adjust for any voltage drop on the 48V side) Since the negative current does not run through the device I guess I could just run another 10AWG to the negative bus bar.

That begs the question of the negative back to the alternator and starter battery. As drawn, it is all going through the chassis. It would not hurt to have a big wire going from the Negative bus bar to the battery/alternator and tie to the chassis there.

 

[FilterGuy]

Maybe consider a 35A dual-pole AC breaker between the shore power plug and the MPP. That could help protect the MPP from bad campsite wiring.

I thought about that... and maybe it is a good idea.

However, I am not sure how it would protect from bad campsite wiring. The primary value is to shut things down if something happened to pull too much current from the shore power.... This could be 1) a short between the plug and the inverter 2) The inverter shorting internally.
Presumably, the campsite has a breaker that would protect the system, but I guess the 'bad campsite wiring' would be a bad breaker on the campsite side that did not blow as it should. (This would be a double fault situation; 1) Something wrong in the bus and 2) a bad campsite breaker)

 

[John Frum]

Do you really need a pre-charge circuit when the in-rush is distributed across 5x batteries?

 

[FilterGuy]

Do you really need a pre-charge circuit when the in-rush is distributed across 5x batteries?

The precharge protects many things:

1) The BMS
2) The switch
3) The capacitors in the inverter. (People have claimed the inrush is a problem to the capacitors.... I am not sure of this).

 

[John Frum]

The precharge protects many things:

1) The BMS
2) The switch
3) The capacitors in the inverter. (People have claimed the inrush is a problem to the capacitors.... I am not sure of this).

Do you really need that disconnect switch?

 

[FilterGuy]

Do you really need that disconnect switch?
It is not mandatory, but I like the idea of being able to totally disconnect the inverter from the DC without shutting down the DC.

 

[FilterGuy]

Something like a Victron battery protect could help deal with low voltage caused by the DC loads. Put it between the DC disconnect switch and the DC converter. Actually, it could replace the DC disconnect switch since the battery protect can be turned on and off like a switch.

I looked at that. The only 48V model they have is 100A and costs $132
I also looked at some other 48V Low voltage disconnect relays that are lower cost but none of them looked very reliable.
I also looked at the Victron 48-12V buck converters (They have LVD capability) but they only do 9A so there would need to be 3 of them.

In the end, we just decided to do without.

 

[rmaddy]

Bummer. 48V does lower the number of options available.

 

[John Frum]

I looked at that. The only 48V model they have is 100A and costs $132
I also looked at some other 48V Low voltage disconnect relays that are lower cost but none of them looked very reliable.
I also looked at the Victron 48-12V buck converters (They have LVD capability) but they only do 9A so there would need to be 3 of them.

In the end, we just decided to do without.

Its less than 10 amps spread across 5x bms.
Is the BMS is the those batteries configurable?

 

[FilterGuy]

Bummer. 48V does lower the number of options available.

Yup. 48V is a little more challenging on a mobile system.

 

[DJSmiley]

Also for the 6-way fuse box

- Its a mega fuse. Lowest available fuse is something like 30 or 40A if I remember correctly
- Lower rated fuses require a midi fuse box (not mega)
- Midi and mega fuses are rated for max 32V. With 48V, in worst case they might just arc and continue to let current pass if shit hits the fan
I know eg Victron has 56V-versions of the mega fuses, but the regular ones are 32V max so you have to be carefull selecting the right one for 48V
( https://www.victronenergy.nl/upload...,-Mega-and-ANL-fuses,-and-fuse-holders-EN.pdf )

And 48V is more like 52-55V depending on SOC...

DC to 12V converter of 30A: You might consider 2 pieces and distribute the load.

If you're running eg a compressor fridge or diesel heater, their startup current is quite high. If the fridge eg starts its compressor while a diesel heater is starting (glowplug on) it might exceed the 30A easily. Don't know about the overload for surge spikes that thing can handle...

 

[FilterGuy]

Its less than 10 amps spread across 5x bms.

The owner opted to start with 3 of the LiFePower4 batteries and expand later if needed.

Is the BMS is the those batteries configurable?

Yes... but it is not Bluetooth. You have to hook it to a pc.