Need Help Adding a Voltmeter

[Cold Beer]

I want to install a voltmeter on my Massey Ferguson 240, currently it only has the dummy light. Since I have just enough electrical background knowledge to burn up my tractor and any surrounding structures, I need some advice on how to properly install the gauge, which wires go where etc.

 

[Soundguy]

i'd check and see if the key switch has a run tab..if so, that would be my choice for a + pickup.

soundguy

 

[Transit]

FYI, not being all that familiar with volt meters, you may find some "Problems" that are not problems.
Digital meters are more sensitive than dial meters, in that they indicate down to xx.1, xx.01 volts. The low order digits may roc some and the voltage across the battery or were ever you make the connection to will also roc because the voltage regulators are not rock solid. Expect to see values in the range of 13.5 to 14.5 v and constantly changing as the regulator will hunt around an average value. You will soon learn what normal is.

 

[Soundguy]

can also install a large value electrolytic capacitor across the back of the gauge to compenstae it a bit. say something like 1000-2200 uf in the 15-25v range.. even up to 6800uf...

soundguy

 

[SPYDERLK]

Since a voltmeter draws almost no current you could hook it directly into the battery circuit before the switch. This gives you continuous reading and the advantage of being able to read your battery V under no load conditions vs the V under various load conditions that are seen when the Ig Sw is on. This can give you comparative values that one day youll find use for in diagnosing problems. Cap is a good idea if your going with a digital gage .. An analog type wouldnt need it, but vibrations are an issue with those.
larry

 

[Soundguy]

Since a voltmeter draws almost no current you could hook it directly into the battery circuit before the switch. This gives you continuous reading and the advantage of being able to read your battery V under no load conditions vs the V under various load conditions that are seen when the Ig Sw is on. This can give you comparative values that one day youll find use for in diagnosing problems. Cap is a good idea if your going with a digital gage .. An analog type wouldnt need it, but vibrations are an issue with those.
larry

I agree..the cheap non compensated gauges ( analog or digital ) are gonna be the less accurate .. digital are easy to compensate.. the analog with touch movements.. well.. not much to do for them.

I know some people put them on push buttons for momentary or on/off checking.. or automagic with key switch or by a sender like on oil pressure line.

lotsa possibilities

soundguy

 

[Transit]

Without going off the deep end into the electronics, i don't think adding a large cap will have any influence.

 

[Soundguy]

It will.. and yes.. you'd have to go off the deep end to know or explain why. Slew rate and 'averaging' will be part of the picture.. can get fancy and add an inductor.
looking at a PI or an L filter and thinking about emi/rfi filtering will be helpfull in working with non compenstaed gauges... ( won't do much for non dampened analogs though.. ) that are just plain jittery due to inertia..

soundguy

 

[SPYDERLK]

Without going off the deep end into the electronics, i don't think adding a large cap will have any influence.

Some cheap electronic/digital meters dont deal well with quickly changing voltages. A charging waveform is not a true, reasonably steady state DC, but instead its a series of hi frequency pulses that average out to DC. The digital meter is not updated real time - it samples at some rate not atuned to the charge pulses and its displayed value can jump around because of this. A cap across it would serve to average the pulses and steady the meter reading. ... or use an analog meter. The mass of its meter movement averages the pulses - no cap needed. Unfortunately, tractor vibes will shorten its life some.
larry

 

[Soundguy]

yeah.. what he said. same reason why I hate cheap-o digital auto rangeing meters with no set-scale function...

soundguy

 

[Transit]

Agreed Larry. Being that the voltage regulator is a voltage comparator that switches on-off, signaling the altenator to charge the battery to an upper limit say, 14.5 volts. At 14.5 v + the regulator is switched off and the battery is allowed to float, it's voltage sinking to a lower limit say, 13.6 v, than switching on again. On-off-on-off...... depending on what the electrical load is at the time, lights or not, the repetition rate will be fast or slow. Adding a capacitor will change the R x C time constant of the circuit, a large C will stretch out the reaction time, slowing the jitter. However, the mane purpose of the electrical system is to start the engine, that requires a large amount of energy for a short time and that translates into lots of amps with very, very little voltage drop, meaning low, low resistance. Now we're talking 0.01 Ohms. Now 6,800uf x 0.01 ohms = 0.00068 seconds. The reaction time of the charging system is much, much longer, maybe one second, than the RC time constant of the cap. Like I said, not much help. See, I had to go off the deep end.

 

[Soundguy]

we don't care about the meter jiggle at startup.. just during normal operation.

soundguy

 

[SPYDERLK]

Agreed Larry. Being that the voltage regulator is a voltage comparator that switches on-off, signaling the altenator to charge the battery to an upper limit say, 14.5 volts. At 14.5 v + the regulator is switched off and the battery is allowed to float, it's voltage sinking to a lower limit say, 13.6 v, than switching on again. On-off-on-off...... depending on what the electrical load is at the time, lights or not, the repetition rate will be fast or slow. Adding a capacitor will change the R x C time constant of the circuit, a large C will stretch out the reaction time, slowing the jitter. However, the mane purpose of the electrical system is to start the engine, that requires a large amount of energy for a short time and that translates into lots of amps with very, very little voltage drop, meaning low, low resistance. Now we're talking 0.01 Ohms. Now 6,800uf x 0.01 ohms = 0.00068 seconds. The reaction time of the charging system is much, much longer, maybe one second, than the RC time constant of the cap. Like I said, not much help. See, I had to go off the deep end.

I was speaking of the hi frequency pulses in the rectified AC from the alternator -- a function of rpm, and a source of confusion to a sampling/electronic meter. True, the cap wouldnt be needed with the slowly repeating transients you are bring up.
larry

 

[SPYDERLK]

Gee, let's not scare the pants of the guy with RC time constants and waveforms. He didn't even mention analog or digital. I think an analog would be best, and many of the automotive types are damped movements anyways. The though of connecting right across the battery isn't all bad either as log as the tractor doesn't set for long periods of time. Hopefully, we'll get an update or another question.

Good thinking. I like the analog idea too but am worried about vibration on some tractors. Not usually enuf to be an issue in automotive. Check me on this, but Im pretty sure an analog is going to draw 0.001 to 0.010 A. More than that and the meter would start getting a bit warm. The low end is less than an Amp Hr per month, and were talking 30 or 40AH batteries. By internal leakage the battery self discharges a bunch more than that all by itself -- at least for the 1st few months. The accepted figure is 5% per month.
larry

 

[crazyal]

If it was me I would add a hour meter at the same time if your tractor doesn't have one. I would tap into the ignition switch (output side) for power and run a wire directly to the ground on the battery. I would use that same power for any lights the meter(s) have built in if they have their own wires. I think I would just stick with an analog style gauge, they are simple, cheap and usually accurate enough to let you know if things are working as they should.

 

[Transit]

Will Larry, the only way to know for sure what's going on is to put an O-scope across the battery and alternator output, set up a DVM and test the outcome with various size caps. I still think you'll need a full Farad cap to keep the volt meter steady. And so what if the voltage wiggles some, learn to accept a few thousandths up and down; the moon will not spin out of orbit. As for the meter being a constant drain on the battery, just wire it in on the on-off side of the key switch.

 

[RobertN]

It's just a voltmeter! Really, we could get in to transients and glitches and trans eschemic events. Even to the sun spot polarization of the flux capacitor. I have stuff at work to measure sub fempto-second timing, and read sub fempto-amp current.

Get a decent quality volt meter, and install by the instructions in the box. Just remember, most are not waterproof, so if you park it outside that might be a problem. Or get a marine/boat rated meter.

Analog gauge is the easiest to read.

One leg goes to ground, one goes to positive.

KISS; keep it simple silly

Will Larry, the only way to know for sure what's going on is to put an O-scope across the battery and alternator output, set up a DVM and test the outcome with various size caps. I still think you'll need a full Farad cap to keep the volt meter steady. And so what if the voltage wiggles some, learn to accept a few thousandths up and down; the moon will not spin out of orbit. As for the meter being a constant drain on the battery, just wire it in on the on-off side of the key switch.

 

[SPYDERLK]

yes, we shouldnt even bring up the finer points. It makes people nuts to even know they exist.
larry

 

[RobertN]

Nah, that is fun stuff. But, it should have it's own thread. Then we could discuss how sun spot radiation affects the electron hole recombination event triggered by an overcharged flux capacitor. Then we can hook up an Agilent 1156B and measure the fempto amp current variation across time and voltage variables.

Even I jumped from Electronics to Emergency Medical Tech; hate those trans ischemic events...

yes, we shouldnt even bring up the finer points. It makes people nuts to even know they exist.
larry

 

[Cold Beer]

Gee, let's not scare the pants of the guy with RC time constants and waveforms. He didn't even mention analog or digital. I think an analog would be best, and many of the automotive types are damped movements anyways. The though of connecting right across the battery isn't all bad either as log as the tractor doesn't set for long periods of time. Hopefully, we'll get an update or another question.

I'm going to use the stock analog voltmeter gauge from Massey Ferguson, nothing fancy like digital or voice announcing.
It matches the other factory gauges on the tractor for that year model.

I want to add an oil pressure gauge also. I just don't like dummy lights keeping me informed of volts and oil pressure.

The tractor is used about 3 times a week during grass cutting season and not so much in the winter.

Below is the gauge I ordered.