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Voltmeter wiring

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ThunderGuts
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Joined: 13 Nov 2018
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PostPosted: 08:40 - 11 Sep 2019    Post subject: Voltmeter wiring Reply with quote

Morning all,

Following on from the thread in General, I've got a voltmeter landing soon. It's a simple two wire affair and I obviously don't want the thing lit up when the ignition is off. So . . . this shouldn't really be a difficult question and I feel a bit daft for asking it, but if I connect the negative to earth/battery negative terminal, is it just a case of identifying a wire that's got power when the ignition is on (somewhere behind the clocks) and tapping into that to power the voltmeter? Something like the clock lights maybe, assuming they're 12v?

I am making a big assumption here . . . that the 12v parts of the system are going to reflect the battery voltage . . . if not I guess the alternative is to hardwire it to the battery with a switch so it can be turned on and off, but this would be a bit faffy.

Cheers
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Islander
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PostPosted: 08:51 - 11 Sep 2019    Post subject: Reply with quote

Yep. Find a suitable ground and a switched 12v. I'd include a fuse inline somewhere as well...
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ThunderGuts
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PostPosted: 09:04 - 11 Sep 2019    Post subject: Reply with quote

Islander wrote:
Yep. Find a suitable ground and a switched 12v. I'd include a fuse inline somewhere as well...


Cheers. Presumably a low value fuse will be sufficient?
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ThunderGuts
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PostPosted: 09:42 - 11 Sep 2019    Post subject: Reply with quote

Any reason I can't connect to one of the feeds to the fuses? Just thinking it's in a nice sheltered location so an inline fuse wouldn't need to be waterproof like it'd need to be if it's somewhere around the instrument cluster. It'd also mean I wouldn't need to take the clocks off (which is problematic due to a stripped thread - it's possible, just faffy)
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ColinK98
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PostPosted: 10:07 - 11 Sep 2019    Post subject: Reply with quote

i have my voltmeter taking a live feed off the front light as this comes on when ever the bike is running.
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jaffa90
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PostPosted: 10:23 - 11 Sep 2019    Post subject: Reply with quote

I velcro`d one of these to the middle of the handlebar,

https://www.ebay.co.uk/itm/12V-Digital-LED-Display-Voltmeter-Voltage-Gauge-Panel-Meter-Car-Motocycle-BSG/122894221375?hash=item1c9d11003f:g:FdkAAOSwighZfxVY

Took a live from the front brake switch and earthed to the bar.
It was only a temp monitor.
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stinkwheel
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PostPosted: 10:26 - 11 Sep 2019    Post subject: Reply with quote

Be aware that depending on where n the loom you attach it, you can get varying voltage readings and real variation when you turn things on and off.

As such, probably the best place to fit it is in onto the main feed coming back from the ignition switch to the fusebox which will give you a reading as close to the level of the battery as possible while still being switched.

You CAN use any switched live but if you use the headlight one, you'll read a comparatively larger drop in voltage when you put the lights on than if you measured at the battery.

This is not necessarily a problem because you're more looking at differences in how the voltage sits during normal riding/rest than the outright voltage. If the regulator failed giving an over-voltage, you'd see that. Also interesting to see how quickly it recovers to normal after starting, that's a good indicator of battery health.

So for example. I fitted mine in the feed to my accessory relay because that was a convenient place for it. My VFR normally sits at 13.6V with the headlight on. It's recently dropped to 13.3V which makes me suspect the battery is starting to flag. However with the lights off, it still sits at 14.2, which is what it did with a brand new battery suggesting that's the maximum charging voltage reading at that point in the loom. The regulator has kicked in at that point. If I were to measure the voltage at the battery, it would be slightly higher. If I use my heated grips I get a comparatively large drop on my meter but I know this is because of where the meter is located rather than because of a fault.

Of course, as all enfield owners know, ammeters are where it's at.
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dynax
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PostPosted: 10:50 - 11 Sep 2019    Post subject: Reply with quote

When i fitted mine i used a waterproof electrical box mounted on the bars and took a power cable direct from the battery, everything is swithched apart from the clock which is on all the time Thumbs Up
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WD Forte
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PostPosted: 14:55 - 11 Sep 2019    Post subject: Reply with quote

I've got one o them wee domed ones on the way too
always handy to have a VM on the bike.

A good ground connection and a switched live which will already be fuse protected
is all it needs IMO.
While all things are possible, its highly unlikely a milliamp eating gauge will
cause a dead short so I wouldn't bother to give it its own fuse.
Just make sure the wires and terminals are well insulated from weather and
chafing/shorting.

As with any gauge, it's best checked from time to time.
by comparing a (good) meter reading across the battery terminals
when off/running/running with lights on, to what the gauge says.

It should be reasonably accurate to within say 0.1 of a volt
but you may have to allow for location and load.
Once you know its behaviour you should be able to trust it to
give you a good idea of the battery and charging state.
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Islander
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PostPosted: 15:50 - 11 Sep 2019    Post subject: Reply with quote

ThunderGuts wrote:
Islander wrote:
Yep. Find a suitable ground and a switched 12v. I'd include a fuse inline somewhere as well...


Cheers. Presumably a low value fuse will be sufficient?


Yes, low value - it won't take much current. Remember fuses protect the wiring not the device.

I'd use the main ignition feed after the ignition switch and the fusebox.
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Polarbear
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PostPosted: 16:44 - 11 Sep 2019    Post subject: Reply with quote

One thing to remember -

For a check of the battery condition rather than alternator/regulator output you should wait at least an hour after running the bike or charging or whatever. The battery will settle at it's standing voltage which will give a rough idea as to its cell condition and the charge it is holding.

It's more accurate to use a hydrometer but who can be arsed with that on a bike battery. Laughing

As a rough guide I use this to check boat batteries (my bowthruster ones sit at 12.2 and are pretty goosed Embarassed )

Obviously not set in stone as you will probably have cranking problems well before the charge drops very low with a bike battery but another tool for diagnostics.

http://www.traxide.com.au/DATA/S_SoC_Table.jpg
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stinkwheel
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PostPosted: 16:58 - 11 Sep 2019    Post subject: Reply with quote

Polarbear wrote:
One thing to remember -

For a check of the battery condition rather than alternator/regulator output you should wait at least an hour after running the bike or charging or whatever. The battery will settle at it's standing voltage which will give a rough idea as to its cell condition and the charge it is holding.


However, also a case of the act of observation altering the result of the test.

If your voltmeter is on a switched live, it can only measure voltage when the ignition system (and lights, fuel pump and FI on a modern bike) are powered up. So best bet is to get a reference value when the battery is new.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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ColinK98
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PostPosted: 09:54 - 12 Sep 2019    Post subject: Reply with quote

stinkwheel wrote:

If your voltmeter is on a switched live, it can only measure voltage when the ignition system (and lights, fuel pump and FI on a modern bike) are powered up. So best bet is to get a reference value when the battery is new.


if you are having charging issues.
then it is the voltage to the battery while everything is turned on that is of interest no ?
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ThunderGuts
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PostPosted: 11:54 - 12 Sep 2019    Post subject: Reply with quote

ColinK98 wrote:
stinkwheel wrote:

If your voltmeter is on a switched live, it can only measure voltage when the ignition system (and lights, fuel pump and FI on a modern bike) are powered up. So best bet is to get a reference value when the battery is new.


if you are having charging issues.
then it is the voltage to the battery while everything is turned on that is of interest no ?


It's charging (or more specifically, voltage delivered to the battery) that's of interest here. Even so I reckon it'd show a reasonable picture of the battery pre-starting as this is a carb'd bike, the headlight doesn't activate until the starter motor has fired so there's sod all draw on the battery until it's started.
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stinkwheel
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PostPosted: 12:23 - 12 Sep 2019    Post subject: Reply with quote

ColinK98 wrote:


if you are having charging issues.
then it is the voltage to the battery while everything is turned on that is of interest no ?


Yes, but we were specifically discussing looking at resting voltage as an indicator of battery condition there. Something a voltmeter fitted to a switched live could not provide.

It occurs that what they used to do (on the kawasaki GT750 which had a voltmeter on the dash) was have the voltmeter connected directly to the battery which was connected through a normally-off intermittent switch. When you press the button, it gives you a voltage reading, even if the ignition is off.

Just another way of doing things...

In fact, you could potentially have it connected to a switched live AND the battery with intermittent switch. So it would give you a dynamic reading for charging when the engine is on and a spot-reading of resting voltage by pressing the button when the engine is off.

I realise this is totally over complicating the matter.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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ThunderGuts
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PostPosted: 13:18 - 14 Sep 2019    Post subject: Reply with quote

Simple install complete. Took a feed from the ignition live. Seems to be sod all loss but the meter is out by 0.2v compared with my multimeter. Works well. Funnily enough I’ve always cursed the brake reservoir having the sight facing away from the rider but that blank face was perfect to attach the sticky pad for the meter to 👍
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Polarbear
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PostPosted: 16:23 - 14 Sep 2019    Post subject: Reply with quote

ThunderGuts wrote:
Simple install complete. Took a feed from the ignition live. Seems to be sod all loss but the meter is out by 0.2v compared with my multimeter. Works well. Funnily enough I’ve always cursed the brake reservoir having the sight facing away from the rider but that blank face was perfect to attach the sticky pad for the meter to 👍


Looks quite neat Thumbs Up
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