Power diversion for van solar/LiFePO system

[Oberon Robinson]

Just came across this project, and wow!  It's the missing puzzle piece I needed to make everything come together.  And the fact that it's open sourced.... I'm an open source guy from way back, as well as a fellow Canuck solar enthusiast.  I just can't express how grateful and excited I am to discover this!

Anyway, I have a few questions to help figure out exactly which ElectroDacus components to order.  I'm building a van solar system, and I've got 8x 280Ah prismatic LiFePO cells on their way.  I got a Victron SmartSolar MPPT 100 | 20 and a momentary-power-switch 4000W inverter, before I discovered ElectroDacus - I can still return those if needed.

So my questions:

1.  I'd like to divert excess solar power to a water heater - I assume that if I stick with MPPT, I can just trigger a relay with the EXT IO4 control line, that would divert power to the water heater when charging is turned off, correct?  Also not exactly sure if the particular MPPT I got can be remote controlled, the Victron documentation isn't very detailed.

2.  The inverter I picked up is a Giandel 4000W pure sine wave PS-4000QAR.  I got a good price on it, but unfortunately it doesn't have a physical on/off switch, just a momentary button - it does have a remote, but that also uses a momentary button.  Any idea if it might be hackable to work with an ElectroDacus?

3.  With both an inverter and multiple 12V & 24V DC loads, can they all be switched with EXT IO3?  I assume not with a momentary switched inverter, but otherwise yes, using Victron Battery Protect or some other DC contactors in parallel with the inverter?

4.  I'm planning to add some battery heating pads to keep the cells above freezing in winter, and I was thinking I might add an ESP32 board for some control logic, to turn the heating pads on & off depending on temperature, solar input, battery state of charge, etc.  But is it possible to add in some extra programming right into the ElectroDacus instead?

Thanks very much!

Oberon

[Dacian Todea]

Oberon,

1. Yes you can control that Victron MPPT but you will need this remote ON/OFF cable https://www.victronenergy.com/accessories/ve-direct-non-inverting-remote-on-off-cable  that will in turn be controlled by the EXT IO4 but you will not need that if you get a DSSR20 with diversion as then you can add the DSSR20 betwen PV panels and MPPT (assuming you want to keep the MPPT as it will likely offer no benefit depending on what PV panels you have).

2. There is a hack to convert the momentary switch + the power LED in to what SBMS0 require if you like that inverter  https://groups.google.com/g/electrodacus/c/M8fe1VRLtYw/m/FokPNKT5AwAJ

3. Yes you will need something like a Victron Battery protect for the small DC loads and that hack above for the inverter and Yes the EXT IO3 can control both of them.

4. The battery box will need to be well insulated else you will need to much energy to maintain battery temperature. But with proper insulated box you should not need more than a 10 to 15W heater to maintain battery above +10C and all you need is a cheap electronic thermostat maybe backed up by a simple bimetal switch.  Without insulated battery box energy needed will be to high and so you will not be able to use your battery when very cold.

No automation will be necessary as 2x 60 cell panels will be able to generate the small amount of heat needed to maintain battery temperature even in cloudy days.

[Oberon Robinson]

Awesome, thanks Dacian!

I did look at that Victron cable but it wasn't clear how it attaches to the MPPT that I have, there doesn't seem to be any kind of socket for it other than the jumper pins.  Anyway you are saying that the DSSR20 will give equal efficiency to MPPT?  I had understood that PWM is generally less efficient overall, but if I'm wrong I'm happy to be corrected and use DSSR20 instead!  I haven't yet ordered my panels, so I can still choose whatever will work best with it - I guess if I have 2x 200W 20VOC panels, that will work well with one DSSR20 to charge my 24V battery, right?

That power button switch hack is brilliant!  I will do that. :)

What is the max output current of the EXT IO3?  I haven't yet come across such specs anywhere, sorry if I missed them.  I don't want to draw too much if I need 2 DC contactors for 12V & 24V loads.

Yes, I am planning to build a well insulated battery box for winter use.  I believe I do need automation for the heater control because if it's night time, battery temp is below 0°C, and the battery goes below set minimum charge, the heat will need to be turned off.  Also probably if ambient temp in the van is way below 0°C the heat should not come on at all.

So if my thinking is right, I should get a SBMS0 and one DSSR20 with diversion for this system, correct?

Thanks again!