Adding dash voltage gauge for trolling motor batteries.

[DunbarLtd]

I have a 30lb thrust minn kota 12v trolling motor that I use 2 group 27 deep cycle marine batteries. I never know how far I am discharging them so i want to add a gauge on the dash to monitor them at all times.
I do not have the batteries hooked up to anything but the trolling motor.
I have a battery selector switch.

Im trying to figure out how to wire in a volt meter. I was wondering If I need to buy a double meter and wire each battery to it or can i somehow wire up both batteries to a single volt meter utilizing the battery switch?

Hopefully that makes sense. Any ideas?

 

[GSPLures]

If you have a battery switch you would just wire it up after the battery switch. It would be off if the switch is off, or read which ever battery is currently being used.

If you want both batteries at the same time you would need one for each battery hooked up to the battery. They may sell one capable of reading 2 different circuits simultaneously but not sure, never looked for one.

 

[Chris1956]

You can use a single gauge, plus a double throw, single pole switch to connect the batteries to the gauge, individually.

I never thought that voltage was an indicator of battery charge. Batteries tend to show 12V+ right up to the point that they are near discharge.

 

[DunbarLtd]

You can use a single gauge, plus a double throw, single pole switch to connect the batteries to the gauge, individually.

I never thought that voltage was an indicator of battery charge. Batteries tend to show 12V+ right up to the point that they are near discharge.

So then how can I avoid overly discharging my batteries out on the water? I got home today after going out and i got 12.32v and 12.41v. Both having been fully charged night before. But what youre saying is once they get to 12v and under I wont be able to tell? If thats so then thats fine. Ill just change batteries when one gets to 12v. But as i have it now I have no way of knowing what the voltage is without pulling out my dvm and lifting the seat which is a pain to do all the time. Having a gauge would make it simple I would think.

 

[bruceb58]

Here is the SOC vs voltage measured with no load at rest

 

[Chris1956]

You are trying to measure hundredths of a volt. Make sure to get a real accurate volt gauge. Make sure to use marine quality, dedicated wiring from battery to gauge for both ground and voltage. make sure to solder all connections, and minimize the number of connections. A small amount of resistance on any part of the circuit will give you a false reading.

 

[DunbarLtd]

Thanks for the suggestions everyone and have a happy holiday!

 

[bruceb58]

You are trying to measure hundredths of a volt. Make sure to get a real accurate volt gauge. Make sure to use marine quality, dedicated wiring from battery to gauge for both ground and voltage. make sure to solder all connections, and minimize the number of connections. A small amount of resistance on any part of the circuit will give you a false reading.

There is no current flowing in the circuit. You will not have any voltage drops from resistance. You can have tons of resistance and it won't matter.

We would often have voltage monitoring ports on circuits through 10K resistors!!

 

[gm280]

There are other options that you may be interested in. They make low voltage indicators for such issues. And then you can add a voltage meter or not, and when the battery gets too low, the indicator comes on letting you know.

I actually have such a circuit I built into my front panel. It allows me to monitor either battery with the voltage meter and if either battery gets too low, I have a low voltage indicator that comes on. And I merely flip a switch to monitor either battery. So it can be setup that way.

 

[DunbarLtd]

Well I found a double voltage meter. I installed it but now i realized it is only 20 amps and my trolling motor pulls 35 amps.

If I set the meter to OFF will the two hot wires still see 35 amps when using the trolling motor? I may have to find a bigger meter?

Thanks for the tips. Merry Christmas!

Here is a drawing i made. The volt meter is ON-OFF-ON switch . Im wondering with the voltmeter in the OFF position will it still see 35 amps on those wires going to the battery?

I am going to be using one battery at a time.

https://imgur.com/ZZBwEVY

 

[Scott Danforth]

a volt meter is wired parallel to the battery and load and has no amperage limit. an amp meter is wired in series and is critical to have a higher rating than the load.

so either you have an amp meter with a ampere rating. or you have a volt meter with no ampere rating.

 

[DunbarLtd]

https://www.amazon.com/gp/product/B01LWXWGXE/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

No amp rating in the description but on the meter it says 20 amps. Im just worried the wires will burn up when im using my trolling motor on high which is 35 amps. It only came with #14 wire.

 

[Scott Danforth]

if its truly a volt meter, your fine. you could have it wired with 22 gauge and it wont mater.

you do realize that is a chinesium volt meter that may have questionable quality. couple that with the fact that it is most likely a copy of a copy of a copy of a copy and they really dont understand what they are building.

in-rush current on your motor is much higher than 35 amps anyway.

 

[dingbat]

https://www.amazon.com/gp/product/B01LWXWGXE/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

No amp rating in the description but on the meter it says 20 amps. Im just worried the wires will burn up when im using my trolling motor on high which is 35 amps. It only came with #14 wirell

Wired in parallel the meter isn’t current limited.

Wired in series the meter is limited to 20 amp

 

[DunbarLtd]

Ok. Makes sense now that I thought about it.

 

[gm280]

The 20 amp rating is for merely for the DPDT switch capability, not the meter. This particular setup wires "parallel" to the batteries. Meaning one of the red leads goes to the positive terminal of one battery, the other black lead of the same pair of wires goes to the negative terminal of that same battery and the other red/black pair of wires goes to the other battery terminals and wires the same. Then you have the option to read the voltage of one or the other battery per the switch... It is NOT supposed to be wired into series with any load, i.e. like the trolling motor. If you try to wire it up that way, you will be buying another meter/switch unit for sure...

 

[DunbarLtd]

So then Im good to go with this wiring schematic?

I have a battery switch with 1-OFF-2 and also option for 1&2.
I will only be using one battery at a time. And using the volt meter switch to monitor the battery i have selected.

I understand parallel and series when connecting batteries in general but the addition of the volt meter when it comes to those two things is warping my brain.

 

[gm280]

So then Im good to go with this wiring schematic?

I have a battery switch with 1-OFF-2 and also option for 1&2.
I will only be using one battery at a time. And using the volt meter switch to monitor the battery i have selected.

I understand parallel and series when connecting batteries in general but the addition of the volt meter when it comes to those two things is warping my brain.

Just always remember, volt meters go in parallel, current meters in series, and you will be good to go...

 

[Silvertip]

You would only need one gauge. The COM terminal on the switch is where the positive lead from the voltmeter attaches. Ground goes to the ground terminal on either battery. If you have BAT 1 selected, the meter will read BAT 1 voltage. Select BAT 2 to read BAT 2. With BOTH selected you will read the voltage of the combined batteries. Make your readings with motor operating otherwise the system is not under load and the reading is basically meaningless. Do NOT confuse AMPS and VOLTs. Two different electrical characteristics. Your motor operates on 12 VOLTs but can draw a maximum current of 35 AMPs when bound up with weeds or when operating at maximum capacity.

 

[DunbarLtd]

I understand parallel and series in general when connecting batteries but adding a volt gauge to this setup somehow warped my brain.

I think Im getting confused because the motor pulls 35 amps but somehow the small wires of the volt gauge do not - even though they are connected to the same circuit. I really need to draw out a proper electrical schematic for this.