Electrical Help

BigBody79

BigBody79

Well-Known Member
Joined
Mar 30, 2005
Location
Lumberton
I have a LED battery gauge I'd like to put on my boat to monitor my batteries while on the water.

I have a 12v starting battery

I have two trolling motor batteries wired 24v

Is there any way I can hook them both to the same gauge and have them on a switch.

ie On-Off-On or 12-off-24?
 
yes as long as you can isolate the other electrical system when you switch the gauge
 
I've looked at that DPDT switch diagram for a long time. Would this work?

1-24(+) 2-24(-)
3-G(+) 4-G(-)
5-12(+) 6-12(-)
 
Make sure the switch is break before make.

Make before break will short the two batteries out. And for good measure fuse the supply wires at the battery
 
a_kelley said:
Make sure the switch is break before make.
Click to expand...

Shouldn't matter. All the hots are on one leg of the switch, all the grounds are on the other leg. If it's make before break, all it would be doing is tying the two batteries together.

But you're right -- fuse all wires at the battery. Because fire sucks.
 
shawn said:
Shouldn't matter. All the hots are on one leg of the switch, all the grounds are on the other leg. If it's make before break, all it would be doing is tying the two batteries together.
Click to expand...


Yes unless the batteries are wired in series, in which case you would short one temporarily since positive of one is tied to the negative of the other.
 
Boat set up has 3 batteries typically.

1 12v for cranking
2 12v in series for 24v trolling

Still doesnt matter.
 
It's more of a problem of putting 24V onto the 12V side, and what the amount of current flow looks like between a high voltage source and a lower voltage sink. If it's a lot, it could weld the switch closed. There's also the matter of whether any electronics on the 12V side are capable of handling 24V and/or whether they have a TVS or other voltage clamp to protect them. Being automotive-type devices, they should be able to deal with short spikes (or even operate at 24V, depending on the application), but not all marine components are designed nearly as well as normal automotive stuff.

Most switches are break-before-make though, so it shouldn't be a problem. You could always use a relay to switch the monitored voltages if it's an issue, and just use the switch to energize the relay coil. Relays are almost never designed to be make-before-break, for reasons like this.

Is this a common ground setup between the 12V and 24V battery banks?
 
Last edited:
Oh, I totally missed the 24V shit.
 
I was going to use this switch

No where does it say make before break or break before make.

Sounds like this is a touch more complicated that I thought.
 
BigBody79 said:
I was going to use this switch

No where does it say make before break or break before make.

Sounds like this is a touch more complicated that I thought.
Click to expand...

It's a DPDT-NO (normally open) switch, which means it's an on ON-OFF-ON, and it doesn't ever connect the pairs of terminals together. Because it's an ON-OFF-ON, it's a 3 position switch, and the middle position doesn't make contact with either set of terminals. This is slightly different than a DPDT swith that's ON-ON (or ON-NONE-ON, same thing), which is a two position and is always connected to one set of terminals or the other.

So that switch is a break-before-make.

It's pretty rare to find a general purpose switch that is make-before-break, because they're mostly used for special purposes or for a specific reason.
 
On off on is what you want. If you leave the gauge on all the time, it'll drain those batteries.
 
In 3 months maybe
 
BigBody79 said:
I have three of them. I could do that. But they need an on/off anyways figured I could get away with one.
Click to expand...

You can use the same DPDT switch for both meters, or even a DPST (ON-OFF) if you want. The meter ground for each meter goes to the battery ground for each battery bank, because there's no reason to run it through the switch if you're using one meter per bank. Then, one set of switch contacts goes to one meter, and the other set to the other meter.
So for the diagram at the top of the page, 3 and 5 would be for one battery bank, and 4 and 6 for the other battery bank. Then one switch would turn on both meters, super simple.

If you already have the meters, I'd use two meters and have all the voltage info you want.
 
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