Battery switch wiring suggestions

Schweg2

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Sep 9, 2020
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Would it be ok to wire this switch on the ground side so I can use a shunt to monitor each battery separately? Attached is a drawing on what I was thinking. Or would there be a better way?
Thanks

54831D24-FB5D-402A-99D0-20A6B7ACAFBB.jpeg
33011B64-F590-4BB5-AD14-5140DCCB89E4.jpeg
 

indalecio

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If you connect the battery with a charge controller, the system will switch on/off during you check with the shunt resistor. It will be problem during the daytime charging status.
 

Zil

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Switches can be on negative cables. I have a system disconnect switch on my battery negative.

With that switch set to 'all', your batteries are connected in parallel. There is no real reason to monitor each separately. Parallel batteries act together as one battery. With that switch set to '1' or '2', your inverter will be handicapped by half your available power.
 

12VoltInstalls

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Switches can be on negative cables. I have a system disconnect switch on my battery negative.
In automotive- and less frequently, marine- people would be surprised how often the negative is switched.
The most readily available example is ‘dome lights’ where almost all the time the lights are hardwired positive(+), straight from the fuse block, and the door switch merely closes the negative(-) for the circuit.
Many fuel injection systems in the past were all powered pos(-) and the vehicle ECM merely completed the circuit.
Never mind the MGs and Saab’s? that were “positive ground.”
 

Schweg2

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My batteries consist of 16 eve 280ah cells and I have 2 packs. (32 cells total) I suppose it would be best to leave the switch on “all”. I had the switch mainly using it as a shutoff.
I went ahead and wired the switch to my positive side which I realize is standard protocol.
 

HRTKD

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My batteries consist of 16 eve 280ah cells and I have 2 packs. (32 cells total) I suppose it would be best to leave the switch on “all”. I had the switch mainly using it as a shutoff.
I went ahead and wired the switch to my positive side which I realize is standard protocol.

The reason I asked what type of batteries you are using is that many of use with DIY LiFePO4 use a BMS that allows us to monitor each battery from our phones. That's what I do to see amperage, voltage as well as individual cell information. My shunt shows the aggregate of the two batteries. Should I care, I fire up the app on my phone to check each battery. The first couple of months after implementation I checked the app a lot. After that, not so much.

A switch like that is handy, but not for what you originally asked for. Should you need to work on one battery but still retain power to the rest of the system the switch makes that possible. My switch is all or nothing, so my entire system is either up or down.

If you tried to monitor an individual battery with the shunt by changing the switch to just that battery you would have to change the settings for your shunt. The Ah capacity would be off.
 
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svsagres

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I guess it all depends on what you’re doing with the shunt. If you’re using it to feed a relatively sophisticated battery monitor (Victron BMV or similar) then doing what you’re proposing will primarily just confuse it. These monitors work by measuring the power in/out of the battery. If you switch batteries out underneath it, it will be confused and not give accurate results. You’d also need to switch the positive feed so that it measures appropriate voltage.
 

Schweg2

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I have a Mpp 5kw inverter, what could I set my max charging amps to? i have each battery pack on its own JBD 200 amp bms. 1640386080227.png
 

HRTKD

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Look at this post for voltages to use:

The standard charge rate for my EVE cells is .5C which would be 140 amps. I have two 4s 12v batteries in parallel so in theory my charging amps could be higher. But I'm not looking to push the cells so hard, so my charge rate is closer to .2C.
 

wholybee

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Your drawing should work. But it is unnecessary. With the shunt on the (combined) negative buss bar, and with the switch on the positive, the meter will still only read the current on the active battery. Because, there is no current to the disconnected battery.
 

rhino

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Switches can be on negative cables. I have a system disconnect switch on my battery negative.
This would most likely mean anything downstream of the positive terminal like a busbar could still accidentally be shorted to ground and why it was recommended to have switch on positive.
 

Zil

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My batteries consist of 16 eve 280ah cells and I have 2 packs. (32 cells total) I suppose it would be best to leave the switch on “all”. I had the switch mainly using it as a shutoff.
I went ahead and wired the switch to my positive side which I realize is standard protocol.
There is no "standard". The battery disconnect switch can be on the positive or the negative. If I disconnect the negative battery connection the positive can not short to anything except the battery terminal itself. Pointing out the systems with a BMS are all switched on the negative side.
It is handy to have a disconnect switch as it is easier than pulling a fuse. I find it much better for electrical operation if I use BusBars to collect all the positive and negative connections rather than multi connections on a switch.
Remember rule #2. Disconnect the battery negative (ground) before working on the system.
 

Zil

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This would most likely mean anything downstream of the positive terminal like a busbar could still accidentally be shorted to ground and why it was recommended to have switch on positive.
See my post number 15.
 

OzSolar

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In automotive- and less frequently, marine- people would be surprised how often the negative is switched.
The most readily available example is ‘dome lights’ where almost all the time the lights are hardwired positive(+), straight from the fuse block, and the door switch merely closes the negative(-) for the circuit.
Many fuel injection systems in the past were all powered pos(-) and the vehicle ECM merely completed the circuit.
Never mind the MGs and Saab’s? that were “positive ground.”
This might be from way out in left field, but I've bumped into so few mentions of this while researching I thought I'd ask. Could you help me understand the reason why I should/shouldn't switch the negative, specifically the master negative on a mobile system?

I'm doing my first "complex" mobile solar/inverter system with pretty much all Victron gear. I'm an electrician (not saying I'm a good one) with a background in both grid tie and off grid solar so I'd like to think I've got a decent grasp of the general concepts, but the mobile twist has got me with a lot of questions I can't seem to find the same answer to twice.

My current plan has the only master switch on the main positive, but I've seen some mentions to having a master switch on the negative but no details as to why. Perhaps it's in addition to having one on the B+ so they can completely isolate the non-factory electrical system from chassis ground for when the vehicle is in for service?

Thank you for any light you might be able to shed on this?
 

timselectric

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Disconnecting either the positive or negative, will open the circuit. Most people prefer the non chasis connected pole. But, i see no reason why it would matter. In fact it could be considered safer. When you Disconnect an automotive battery, it's safer to Disconnect the chasis connected side first. To avoid any potential shortage of the tool used to Disconnect it.
 

Zil

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@Schweg2 , what type of batteries are you using?



I had a '67 MGB GT. That Positive Earth was downright goofy.
Early VW were positive ground. I had a hell of a time getting a radio working with it's negative ground.
 

Zil

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My batteries consist of 16 eve 280ah cells and I have 2 packs. (32 cells total) I suppose it would be best to leave the switch on “all”. I had the switch mainly using it as a shutoff.
I went ahead and wired the switch to my positive side which I realize is standard protocol.
It is not standard on battery disconnects. It depends on why the disconnect is used. To take a battery out of circuit is is common to disconnect the negative.
 
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