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Two voltmeters and connection problems?

Tony K

Member
Hello all,

I'm getting close to the connections stage for electrics in my boat. Most things are straight forward enough but because I have two batteries I have included two voltmeters in the dash panel.

Normally as I understand it, a single voltmeter would be connected to the ignition switch, but I can't do this because it will give me the same reading on both gauges from the battery used for the ignition circuit. I can run a fused connection to each battery respectively but this will be live all the time and the gauges will be on all the time, unless the master switches are off. Is it possible for me to make them work and give accurate readings from each battery while activating them with the other gauges on the ignition circuit?

I think I've created a problem for myself?

Cheers Tony K
 

Tony K

Member
Thanks cowboybob,

But I have two volmeters in the dashpanel with the other gauges ready to go. I think your plan is with one voltmeter and a switch to each 12v source? Am I being dumb?
 

cowboybob

Well-Known Member
Most Helpful Member
upload_2017-6-11_12-39-42.png
You could substitute a SPST switch for the relay. The relay just makes it all easier and more elegant (one less switch on the console...).
 

Tony K

Member
Thanks great work, I would never have figured it out. However, if I had two 12v SPST relays activated by the ignition switch would both voltmeters work at the same time?
 

cowboybob

Well-Known Member
Most Helpful Member
Thanks great work, I would never have figured it out. However, if I had two 12v SPST relays activated by the ignition switch would both voltmeters work at the same time? ...
Yes.
... Sorry also, what amperage make and break relay(s) would you recommend?
Well, the voltmeters will pull very little current (μAs), but for convenience sake, a standard automotive SPST Relay (or equivalent) would be suitable.

Since I don't know your location, look for something that looks like these below:
Relay: upload_2017-6-11_18-51-13.png

and Connector harness: upload_2017-6-11_18-52-8.png

Most automotive parts stores carry these items. A SPDT relay would be fine also: just use the NO (normally Open) pin. Be sure to get the correct connector for the relay you buy.
 

audioguru

Well-Known Member
Most Helpful Member
I don't have a boat so I think about my car.
Doesn't your boat have an engine that drives an alternator and a charger? If so then why do you need a voltmeter? My car does not have a voltmeter and sometimes I have the radio playing for hours without the engine running. The battery has never been dead.
Maybe you use the batteries for running high power heating devices without the engine and its charger running?
Oh, is your boat propelled with a high power electric motor and the voltage drops quickly?
 

JimB

Super Moderator
Most Helpful Member
Exactly AG, you don't have a boat.
The guy is building his boat with an all singing all dancing electrical system, his hobby let him get on with it. All good fun I say.

So your battery has never been dead, aren't you the lucky one.
If you do have a flat battery at an awkward moment, you can always push start the car or get a jump start from a passing vehicle.
It would be an interesting exercise to push start a boat out at sea!
May be that is why he wants two batteries and two voltmeters.:)

JimB
 

Tony K

Member
Thanks everyone, especially Cowboybob. I was getting a bit worried about it. I am still not sure what will happen when the Blue Sea automaticc charging relay is charging both batteries, what the voltmeter readings will show, but the connections will be fine now.

Cheers Tony K
 

Tony K

Member
Just thought cowboybob, Is there any reason I can't wire the relays into the circuit before the voltmeters then they would not be sitting with a live supply to them?
 

cowboybob

Well-Known Member
Most Helpful Member
Just thought cowboybob, Is there any reason I can't wire the relays into the circuit before the voltmeters then they would not be sitting with a live supply to them?
You could.

But if you put the 1/4A fuses close to the batteries (as I tried to show in the schematic), any electrical issues "upstream" would not pose any problems (that I can think of) since the fuses would blow with the slightest load provocation. Two relays at the batteries would also require two additional wires from the console selection switch, further complicating the issue.

Or, you could mount a DPDT waterproof switch in the vicinity of the master battery selector to allow a disconnect for the voltmeters. One more switch to remember to disable, though, when shutting down the boat.
 

audioguru

Well-Known Member
Most Helpful Member
Hee, hee. I never needed to push start my North American car that has an automatic transmission and no clutch.
I bought my first car brand new and it had a crank that I tried one time. It started immediately. My lawnmower started the first time this year on the first pull on its starting cord.
 

Tony K

Member
Thanks Cowboybob, actually both fuses and relays will be about a metre away from the batteries and the console with ignition switch about a metre from them. I think it can be done but I thank you for the options.

Cheers Tony K
 

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