Battery gauge

[pyemaster]

Hi all

Looking to install a couple of little voltmeter gauges to show the state of my starter and auxiliary batteries.

From what I've read I'll need to pinch the live for the starter one from an ignition source (makes sense so it's not permanently on), but obviously for the one to the auxiliary battery I presume I'll need an in-line switch?

If so, I take it that won't alter the accuracy of the reading?

Thanks in advance!
Owen

 

[StarCruiser]

If I were you Owen, if you want accurate readings, wire direct from each battery via a fuse as close to the battery terminal as is practical, then a relay switching the positive to the meter. Use the ignition switched + feed to feed the relay coil with the other side of the coil to earth. That way you get accurate readings only when running.

Or you could just fit one of the Bluetooth monitors to each and view the results on a smart phone. Ctek do one and there's others on eBay.

 

[pyemaster]

Ahh okay, so would that need to be through two separate relays I take it? Both powered through an ignition feed?

So that would be:

- Fused lines from each battery to each relay
- Each relay grounded
- Each relay connected to respective gauges
- Each relay connected into an existing ignition live somewhere
- Each gauge then grounded?

Owen

 

[StarCruiser]

Got it in one Owen.

 

[pyemaster]

Thanks for your help chap, this is a great forum.

Owen

 

[Crispin]

Is there a real need to get as close to the battery as possible?

The meter (should) draw next to no current. So the voltage measured will not be down due to voltage drop over the wire. Besides, the meter measures the voltage at the meter (i.e. the thing in the dash) which you're going to run with thin wire.
You'll lose a few mV at best I'd imagine.

An easy alternative is the BT ones. I'm happy with the one I bought but it has it's own downsides - you cannot glance at the voltage.

 

[Towpack]

Chris,

I think what SC means is take a feed for the gauge direct from each battery, rather than some point in the wiring loom, to get an accurate reading and put the fuse as close to the batt terminal(s) as possible as good practise for the best safety. At least, that's how I read it but could be me that's mis-read it of course. Must admit the BT gauges are a neat idea but, personally, I like a permanent gauge I can check anytime.

 

[StarCruiser]

That's it TP.
The fuse needs to go as close to the battery as practical. That way a short circuit to unfused skinny cable becomes highly unlikely.
You can put the meters anywhere as they will draw minimal current. Just feed them with at least a 10A wire to be mechanically sound (thin wires break easily) and the fuse can be 2A or anything below the rating of the wire you are using.
Make sure the wire to the coils of the relays is at least the same capacity as the fuse in the circuit you are connecting it to.
Use crimp terminals or soldered connections. Sleeving is also good to use to keep the wires neat in the engine bay and route them out of harms way.

All obvious stuff really.

 

[clivehorridge]

OK, to a guy with a small brain and a vocabulary that really doesn't extent to ohms and amperes and such like, on the 80 both batteries are wired in parallel (I do know what that means, surprisingly enough).

So when you put a gauge across the terminals of one battery, unless you disconnect the other, you'll be getting a reading from both, surely, whatever that means of course, an average or something more complicated.

I've read Owen's posts and I've read yours Rich, but for the life of me I've missed the part that would allow one battery to show 10 V and the other to show 12.6 V if that were the case, on separate gauges.

Sorry to be such a numbskul, but surely relays aren't able to separate two batteries wired in parallel are they?

Needless to say, I only have one gauge, and that's wired to one of the batteries, so I'm presuming I'm getting a mean of the 2 batteries on the gauge, unless you advise me otherwise.

At the moment, I don't have any relays or fancy switches, just a fuse on each of the + & - gauge wires, close to the battery as you have previously advised.

The gauge is on 24/7, but the truck is my DD so I'm guessing it doesn't make a lot of difference.

 

[Towpack]

You're absolutely correct Clive. No point in two separate gauges if the batteries are in parallel although they would give a reading for each battery, albeit with them under considerable load, when cranking the engine if the 24v start system has been retained. From the OP's mention of 'starter' and 'auxiliary' batteries I took it to mean that he's either altered his standard battery setup to separate them or maybe has a 3rd battery for leisure/ancillary duties.

 

[pyemaster]

Hi Clive

Sorry to confuse you, yes as Towpack says in the above post I have installed a split charge system on my batteries, so they are not wired together in parallel.

I replaced my original dual batteries with one big 830cca starter and a separate 110ah (800cca) marine battery, before wiring in the split charge system and two auxiliary fuse boxes to tidy up the growing cableage.

I've now got the spotlights, roof lights and sub woofer routed through the starter battery fuse box (as I only need them while running), and my CB radio, air horns, rear work lamp and additional 12v accessory sockets in the back (to charge everything while camping, like phones, tablets, Bluetooth speaker, LED lighting, head torch, etc..) routed through the marine battery fuse box. That way the stuff I might need in an emergency (comms, horn, light) is running/charging off the longer lasting battery too. Hope that makes sense.

Owen

 

[clivehorridge]

Hi Clive

Sorry to confuse you, yes as Towpack says in the above post I have installed a split charge system on my batteries, so they are not wired together in parallel.

I replaced my original dual batteries with one big 830cca starter and a separate 110ah (800cca) marine battery, before wiring in the split charge system and two auxiliary fuse boxes to tidy up the growing cableage.

I've now got the spotlights, roof lights and sub woofer routed through the starter battery fuse box (as I only need them while running), and my CB radio, air horns, rear work lamp and additional 12v accessory sockets in the back (to charge everything while camping, like phones, tablets, Bluetooth speaker, LED lighting, head torch, etc..) routed through the marine battery fuse box. That way the stuff I might need in an emergency (comms, horn, light) is running/charging off the longer lasting battery too. Hope that makes sense.

Owen

Please don't apologies for confusing me with electrickery, I'm confused before I start even thinking about it

Thanks Towpack for your clarification too.

It does make sense now, I was thinking too much of my standard 80, 2 battery set-up for the 24V starter.

Still, I'm pleased to think I wasn't so far out, considering my ignorance on these things