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silverms avatar image
silverms asked

Can the 712 monitor 2 different battery types?

I just got the BMV 712. I'm in the processing of wiring everything up. I have a Lead Acid battery for my pickup in the engine bay. I have a 100mA lithium in the bed as my auxiliary. So my question is can the 712 monitor BOTH batteries or do I need to pick one? It shows a diagram for 2 batteries in the installation but I could find nothing on monitoring 2 different types of batteries. I have the shunt installed between the battery and my dc fuse panel before heading to chassis ground. Would it be fine to have the battery in the engine bay to chassis ground rather than connecting to the shunt and use a bunch more wire? Any help would be appreciated. See the picture on how I planned my system. I don't show the 712 connected to the starter battery since I wasn't sure if it could work.

installation
20191106-222848.jpg (1.6 MiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Hi Silver,

You have 1 small error. The negative of the inverter has to be on the Load side of the bmv's shunt.

You can use the bmv's second input to measure the battery temp, or the starter battery voltage, not both.

Dunno much about the Ctek 25000, is it suitable for lithium?

I cant work out what the Blueseas 9009 is for. A mains/inverter change over switch?

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JohnC avatar image
JohnC answered ·

Hi Silver. Best to apply the BMV shunt to the batt you're 'cycling'. Normally the engine batt would be left alone and used only as a starter unit.

The BMV has an 'auxiliary' functionality though, and can be used to monitor the V of the engine batt as well. That's a thing with a choice of one of 3 options, but if you don't need batt temp or bank midpoint V, then use it as a V monitor of your engine batt.

And oh, your diagram has the shunt in the wrong place - the inverter -ve wire should be going through it too.

And for fun, look through the Victron display van install. Even with every gizmo known to mankind included, they still leave the engine batt as a no-touch-mission-critical item. They chose a different aux function, but could have done otherwise.

https://www.victronenergy.com/blog/2019/06/18/the-victron-van-install/

Edit: Posted before seeing the other comments, but left unchanged.


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silverms avatar image silverms commented ·

Thanks John it is starting to make sense now. I will make sure I put the neg of the inverter after the shunt coming off the battery. Though I may have to change the 6awg to 0awg to reflect the change and still eliminate most voltage drop from the battery to the inverter.

I will not even bother monitoring the battery in the engine compartment.

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silverms avatar image silverms silverms commented ·

Here is a revised version. Is this where the negative should go?

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JohnC avatar image JohnC ♦ silverms commented ·

Yeh, that's the one. Can't speak for the rest of your system (unfamiliarity), but the BMV shunt needs it that way.

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silverms avatar image silverms JohnC ♦ commented ·

I'll know next week if everything goes easy with it.

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klim8skeptic avatar image klim8skeptic ♦ silverms commented ·

Hi Silver,

Just be careful with the change over switch wiring, cos it looks odd.

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silverms avatar image silverms klim8skeptic ♦ commented ·

It may look odd but all it is, is a 2 way switch. You can have it off or you decide which way you want the power to flow. I got to use these switches for different projects in 7th grade tech ed. We used ones up to 4 way. It's as basic as a light switch for wiring and understanding.

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klim8skeptic avatar image klim8skeptic ♦ silverms commented ·

Hi Silver,

As per your diagram it looks like you could connect mains power into the inverters output.

And when using the charger, the ac switchboard is not getting mains.

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silverms avatar image silverms klim8skeptic ♦ commented ·

Your overthinking it. The battery is going to the input of the inverter which will supply power to the Ac panel. So it is getting power. The battery also goes to the dc panel providing it power. Now when I plug into shore power I select which system I will mainly use. The DC or the AC remember if I'm sending power to the DC panel it will go in past the dc side of the selector switch to the ac to do battery charger to the dc panel then onto the battery to charge it then the inverter is connected to the battery hence going back to the ac panel for ac power if I want it. Now if i use the AC side of the selector switch it will head right to the Ac panel. panel. I only want it to supply AC on this side since I still have solar panels which will charge and power the DC side. Lol lots of systems tied together and multiple ways on doing things depending on what you are going for.


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