Hooking up a voltmeter far from the battery

Just wondering whether it'd be good enough to hook up a voltmeter by splicing it into an existing wire? Specifically a wire with a 5 amp fuse by the battery that will be used to power a GPS or perhaps charge a cellphone?

Just wondering how this would affect voltmeter readings, or if it'd even effect it enough to worry about it. (I used both "a-ffect" and "e-ffect" figuring 50% right is better than the chance of 100% wrong....hate those two words)

Alexi

PS - I wasn't even going to put in a datel. I was going to go with one of those LED voltmeters (it stays green at a certain voltage, drops to yellow when you're close, and then red if you're low)

It depends on how much current is (potentially) being drawn through the wire by those other devices. Every piece of wire, connector, switch, relay, etc. between the meter and the battery will have some small but tangible amount of electrical resistance. If there is a lot of current being drawn by the other devices then there will be a proportional amount of voltage drop on those resistances, which will in turn result in lower than actual readings.

The best case is to have the battery volt meter on a dedicated pair of wires going back directly to the battery. Good digital volt-meters do not draw very much current (only a few milliamps) so the voltage drop on the wires, connectors, relays is minimal. A GPS or RD doesn't draw much current either, but the error will be somewhat higher than a dedicated wire pair.

PS - good choice on the panel meter vs the idiot lights. There is a lot of information that you can get from the meter that just isn't available from 3 LEDS.

PPS - I think pretty much everyone is effected by the affect effect.

Secondary question....

Wire draw, GPS draw, etc will affect it. That I understand. But I'm guessing it'll show a lower voltage than what is actually being put out by the battery.

So really, since it'd show a lower voltage than what is actually being produced, it actually creates a small safety buffer anyway, right? And are we talking about hundredths of volts difference by splicing into a gps charge or tenths? If its hundredths, I'll just splice in. If tenths of a volt, I'll bite the bullet and run another positive lead and only splice into a ground.

Alexi

I use a similar setup to what you describe. I use the voltmeter that is built into my Escort radar detector. The circuit that charges the detector also provides current for my GPS. I do find that the voltage reading is a little lower because of the wiring, and it often fluctuates between two numbers. Overall, not the perfect solution, but it is acceptable. I had to learn what numbers on the meter were normal with a good battery and light load so I can tell when things have changed.

Alexi said:

Secondary question....
Wire draw, GPS draw, etc will affect it. That I understand. But I'm guessing it'll show a lower voltage than what is actually being put out by the battery.

So really, since it'd show a lower voltage than what is actually being produced, it actually creates a small safety buffer anyway, right? And are we talking about hundredths of volts difference by splicing into a gps charge or tenths? If its hundredths, I'll just splice in. If tenths of a volt, I'll bite the bullet and run another positive lead and only splice into a ground.

Alexi

Click to expand...

That would depend on how much resistance is in the feed wire, and that information we do not have. It would be in the 10ths of a volt or you would never even notice it.

Geezer said:

I use a similar setup to what you describe. I use the voltmeter that is built into my Escort radar detector. The circuit that charges the detector also provides current for my GPS. I do find that the voltage reading is a little lower because of the wiring, and it often fluctuates between two numbers. Overall, not the perfect solution, but it is acceptable. I had to learn what numbers on the meter were normal with a good battery and light load so I can tell when things have changed.

Click to expand...

Ok. I can understand that. I can hook it up to my accessory outlet (this outlet doesn't charge accessories, or rather VERY rarely does), and just ride around for a while without anything plugged in. That'll be my "base" number. Then just use it to see if my battery is getting charged back to my "base" number between rides. Works for me!

Fred W said:

That would depend on how much resistance is in the feed wire, and that information we do not have. It would be in the 10ths of a volt or you would never even notice it.

Click to expand...

Ok. I don't expect much resistance, but this outlet IS plugged into some sort of harness that splits out power.....

I guess I'll do a little testing. I have an SAE outlet that is direct connected to the battery. I can measure the difference between having it right at the batter and then see what it shows when I'm connected to the accessory plug. Even better, I can test my personal voltmeter against the datel, at both places together, and separately. Get some good numbers.

I think overall though, it shouldn't be too much of an issue to attach it to this switched outlet. I don't expect to tax my battery much. It's a precaution to check for a bad battery.

Alexi

Sounds like a decent plan.

But you may be somewhat surprised at the difference between the voltage you measure on your battery tender's cable (right from the battery) and the voltage midway down the wiring harness (from the accessories socket on the glove box). Remember that all of the electrical loads for the entire bike (minus only the radiator fans and the starter motor) runs through the main contacts in the key switch. That's why that switch melts down. All that current going through the contacts results in an appreciable voltage drop across the switch.

Fred W said:

Sounds like a decent plan.
But you may be somewhat surprised at the difference between the voltage you measure on your battery tender's cable (right from the battery) and the voltage midway down the wiring harness (from the accessories socket on the glove box). Remember that all of the electrical loads for the entire bike (minus only the radiator fans and the starter motor) runs through the main contacts in the key switch. That's why that switch melts down. All that current going through the contacts results in an appreciable voltage drop across the switch.

Click to expand...

Wow, Really? I wasn't aware of that.

The way I hooked up my voltmeter shouldn't be affected however (I think): I installed an 'accessory' relay on a pair of leads located about 8 inches from my battery. It is protected by a 15 amp in-line fuse. The relay is tripped by my head light coming on. This way anything running of my accessory circuit can't drain the battery if left on while the bike is not running. (I have another circuit for that, wired into my tank bag. for charging phones, etc.) The accessory circuit is used only for my heated grips right now.

I attached the leads of the volt meter to the circuit just down stream of the relay. so when the bike is running I can monitor voltage. As I flick on various lights, grip heaters, even the brake light I can detect voltage drops.

I use it primarily in the winter when I'm running heated gear along with grips and maybe driving lights.

Given Fred's information above I think its very important to power accessories not using the switched ignition circuit.

Fred W said:

Sounds like a decent plan.
But you may be somewhat surprised at the difference between the voltage you measure on your battery tender's cable (right from the battery) and the voltage midway down the wiring harness (from the accessories socket on the glove box). Remember that all of the electrical loads for the entire bike (minus only the radiator fans and the starter motor) runs through the main contacts in the key switch. That's why that switch melts down. All that current going through the contacts results in an appreciable voltage drop across the switch.

Click to expand...

Hmmm....good point. Lots of harnesses and splits involved with the stock accessory outlet.

Aw jeez. Alright. I'll take the time to run a dedicated positive line to the outlet and put a switch in the glovebox. Just will tap into a ground.

Alexi

OK, but the ground point can also result in metering error. That same current that goes through the wiring harness goes back to the battery and alternator via the ground path. Granted, the frame is a pretty low resistance conductor, but... Since you'll be running wires anyway, why not just run the dedicated ground wire back to the battery too? That way you know for absolute certainty that, as long as your meter is functioning correctly, what you are reading is the battery / charging voltage unaffected by outside influence.

I started out with my Datel panel meter tied into a relay switched terminal strip that had other accessories wired from it. I couldn't live with the error caused by the voltage drop (from the other accessories) across the relay contacts. I have since run dedicated fused wires through a dedicated ignition switched relay so that I know what I'm reading is right. It allows me to adjust my power usage without risking depleting the battery. It also gives very early warning of a pending battery failure. A few tenths of a volt difference may be the clue to a future letdown.

Fred W said:

OK, but the ground point can also result in metering error. That same current that goes through the wiring harness goes back to the battery and alternator via the ground path. Granted, the frame is a pretty low resistance conductor, but... Since you'll be running wires anyway, why not just run the dedicated ground wire back to the battery too? That way you know for absolute certainty that, as long as your meter is functioning correctly, what you are reading is the battery / charging voltage unaffected by outside influence.
I started out with my Datel panel meter tied into a relay switched terminal strip that had other accessories wired from it. I couldn't live with the error caused by the voltage drop (from the other accessories) across the relay contacts. I have since run dedicated fused wires through a dedicated ignition switched relay so that I know what I'm reading is right. It allows me to adjust my power usage without risking depleting the battery. It also gives very early warning of a pending battery failure. A few tenths of a volt difference may be the clue to a future letdown.

Click to expand...

Yup. Tomorrow's goal is to tear the bike apart and prewire for a voltmeter. Dedicated positive and negative power cords. I will be wiring into a 5-blade relay. So the voltmeter will turn on with switched power as the trigger. The center blade (normally closed) will go to a momentary switch (pushbutton) in the glovebox. So if I wanted to check the voltage, I just open the glovebox and press the button. And then when I turn the bike on, it turns on until I turn the bike off in which case the momentary switch will be active again.

In my mind it works great. We'll see in a few weeks when my B-day comes around and I get my datel in whether it transferred from my mind to reality correctly.

Alexi

I am planning a voltmeter install as well, also using a 5 pin relay (to control the ground side of the meter). I'm thinking that rather than adding a switch for checking the battery when the bike is switched off I can use an existing one. The up wire to the windshield looks like a great candidate.

The windshield control switch probably isn't a good choice. Both "up" and "down" are normally closed switches. Both control wires are normally shorted to the return (ground) bus. When you press "up" or "down" the associated wire is open circuited -- disconnected from the return bus.

My plan (parts have been around a while, just haven't gotten around to the implementation yet) is to install the Voltmeter in a small project box with a On-Off-(On) SPDT switch wired to an SAE connector. I'll have this connected to my fused Tender lead from the battery. That way I can On or Off as I wish regardless of key state. I'll have to remember to leave it off when I park the bike, but that shouldn't be a problem. Another benefit is another SAE connector with probes attached turns it into a voltmeter for troubleshooting on the road.

FJRGuy said:

My plan (parts have been around a while, just haven't gotten around to the implementation yet) is to install the Voltmeter in a small project box with a On-Off-(On) SPDT switch wired to an SAE connector. I'll have this connected to my fused Tender lead from the battery. That way I can On or Off as I wish regardless of key state. I'll have to remember to leave it off when I park the bike, but that shouldn't be a problem. Another benefit is another SAE connector with probes attached turns it into a voltmeter for troubleshooting on the road.

Click to expand...

This is essentially what I've done on one of my other bikes (Pegaso) and I don't have any problem remembering to shut it off when parking overnight. The good news is that if you happen to forget it is no big deal. Unless left for very long time the paltry current draw of a Datel meter will not drain the battery.

Constant Mesh said:

The windshield control switch probably isn't a good choice. Both "up" and "down" are normally closed switches. Both control wires are normally shorted to the return (ground) bus. When you press "up" or "down" the associated wire is open circuited -- disconnected from the return bus.

Click to expand...

Good catch, and thank you!

Who woulda thunk it?

Plan B....Horn button.

I know this is an old post but I just added a switched voltmeter and thought I would post it up. I used this meter: https://www.datelmeters.com/cgi-bin/webshop.cgi?config=ent-rounddc and where I placed it seems to work well with visibility while I am underway..