FYI Looking at house battery volts - Digilevel vs. Magnum Inverter Controller

[Neal]

As I've posted recently I'm in Casa Grande, AZ and as I have to pay for electricity here for long term stays, and it's expensive, I'm putting my 1800W solar to use and @Chuggs and I have been having some fun with the solar usage and various other settings, demands on nearly 4 year old batteries (8) etc. When I first started this I decided to use the TIME control option to tell the Magnum system when to use solar which as of this writing is not from 1 AM until 5 PM. This window has widened a little bit from the start which was 9 AM to 4:30 PM by seeing that I'm discharged at about 3% SOC per hour. Mornings were down to around 81-83% so I moved my start window earlier to use more battery and less shore power such as for evening furnace heating as they draw some pretty good amps.

Initially I had a LBCO (low battery cutoff) hit with the Keurig which I had LBCO set to 11.0. A simple spike shut me down which is unfortunate, I wish Magnum didn't react to a single spike or whatever it is they are programmed to. It needs to be a more stable reading which is why many of us like the ME-BMK and ME-ARC50 to get SOC (state of charge - percentage) which doesn't have the fluctuations. As I'm living in the coach, it's not in storage, and I don't want a spike shutdown I moved my LBCO down to 10.0. I'm not sure if there is even an OFF or disable but that would be preferred for this setting actually as again, I'm watching my electricals closely daily.

Anyhooo, reason I'm writing is this morning was an interesting discovery. As I discussed with @Chuggs I never saw the LBCO hit in the Victron web portal (VRM) that records all of the electricals and solar data for review real time and historical. As I recently changed my TIME CONNECT window to 1 AM I ran SOC a little lower, this morning it was down to 80% which is still good. I used my hot water boiling thingy for making french press coffee which is a high wattage demand and watched my digilevel for house battery voltage. It never got below 11.2 which is good, it was pretty stable around 11.4 to 11.6 during the high demand of boiling water. My GEN started and that was a WTF moment as I know it's tied to SOC which is set to come on at 60% SOC (shore power at 65% SOC so it's a fall through). I immediately killed the GEN as it's around 7 AM (quiet hours was OFF due to my recent boondocking). I had never had the GEN start on voltage but in the GEN setup is a Voltage window which was set from 11.4 to 13.5 I believe. So obviously Magnum saw a steady voltage I guess at or below 11.4 and started the GEN. Quiet hours have been set again to ensure this doesn't happen again. But it was odd as I was focused on SOC for GEN and didn't think Voltage was in play.

As this story gets longer the reason I'm writing is I typically watch voltage on the Digilevel which is the panel also used to view tank levels. I also have a BMV-712 which is pretty much on track with the Digilevel. However if you press METER on the Magnum control panel you get instantaneous and actual voltage the Magnum inverter is seeing which I never really payed attention to, but now will. Interesting it can be quite a bit different and this is what I need to watch when seeing what the demands are when the furnace runs or the hot water boiler, etc.

Always learning, nearly 4 years in and still getting little surprises like this.

 

[Kevin D Pem]

@Neal so what size wire feeds the inverter? Your picture shows voltage drop at the inverter.

I haven't seen a sense wire on inverters, but think it would be a good idea.

Only solution I have found is very large feed wire to reduce the resistance. But then again, the drop out voltage may become a problem. Personally I use paralleled feed wire, one from each bank to assure equal battery drain.

As time goes by, you will spend less time watching the numbers.

 

[RKins]

Is your Digi showing that your house batteries are dead?

 

[Neal]

Is your Digi showing that your house batteries are dead?

No, you can see the image above. It's just different between the two.

 

[redbaron]

A man with 1 watch knows the time.
A man with 2 watches never does.

 

[Neal]

 

[RKins]

No, you can see the image above. It's just different between the two.

Oh, I thought anything less than like 12.2V is dead

 

[Buly]

Running anything with electric motor with voltage below 12V will damage it sooner or later.

 

[Kevin D Pem]

Oh, I thought anything less than like 12.2V is dead

12 v on sitting batteries. However inverters are mostly set to kick out at 10 or 10.5 due to voltage drop because of resistance in the system under load.

This does not bring down your batteries completely but once sitting the voltage will read about 12.2 roughly 50% charge.

It is virtually impossible while in use to determine state of charge with out a BMS that has been set up with a fully charged battery.

 

[Neal]

There are TWO "BMS"'s on my setup (Magnum BMK paired to the inverter) and a separate Victron BMV-712 paired into the Victron stack of MPPT and Venus GX. The picture is showing under load such as a hot pot boiling water or a Keurig starting up. This is not stabilized voltage and why I ran my LBCO down to avoid complete shutdowns from a single spike below my setting. I use 11.0 but Newmar recommends 11.9 which should be 50% discharge of your batteries. Again, there are horrendous spikes depending on the demand is not the actual voltage of the 900 aH battery bank, just an instantaneous load.