B7100 alternator voltage

[Eise]

I am installing some gauges and I just put in a amp-gauge and when the tractor is running at idle with the lights on the needle dips to the negative side and stays there until I rev it up. I have an older type B7100 with the alternator behind the fan, it's the two wire type. When I measure the output it reads 8 volts AC at idle, this seems low to me, does anyone know what the AC output voltage should be at idle?

 

[twomany]

It depends on the state of charge in the battery.

 

[Eise]

I don't think the old type of alternator on a B7100 has a regulator built in, the regulator is behind the dash. So the output of 8 volts AC is the unregulated output of the alternator, with the alternator disconnected from the rest of the tractor.

I think the output should be over 12 volts AC right?

 

[Eise]

I'm starting to think the regulator may also be bad, I've looked around the forum but I can't really find how to determine is it is indeed bad. I've tried measuring the DC output of the regulator with the engine running, it just reads 0 volts. But when I connect it back up it does seem to give some output. (atleast that's what the amp gauge tells me) Does the regulator need to be hooked up to the battery in order to work?

 

[07wingnut]

I believe what you have is a dynamo, which puts out single phase AC on those 2 wires. They are notoriously poor at generating a decent AC voltage at low rpm, and reading a discharge at idle, with the lights on, is probably normal.

 

[Eise]

Maybe, but I reckon it's making about half the power it should, 8 volts AC at idle is about half what other people get (from what I've read online) and when I measure the resistance of the dynamo I get 0.8 ohms, which is double of wat other people measure.

My guess now is that half the coils in the stator aren't working. I think I have little other option than to remove the dynamo and open it up..

Does anyone know how the stator is wired?


Edit: I know the stator has 8 coils, could it be that it's two series of 4 coils in parallel?

 

[85Hokie]

Be very careful with AMP gauges....depending on the type, the though type must have all the current through it - thus a large gauge wire, shunt types and others are different.

YOUR machine has a DYNO - it when close to WOT will produce something close to 30 volts .....AC!

Once it goes through the regulator - stepped down to a normal 14 ish volt and gets converted to DC.

As for the Dyno - there are permanent magnets and of course the coil, which if not mistaken is one close loop making up 8 poles.

Here is a picture of the "guts" - this is one that the two sets of bearings decided to take a little permanent vacation!!!

 

[100 td]

Your dynamo is rated at about 10 amps, at rated engine speed, as it's a dynamo (permanent magnet generator), not an alternator, it's output is related directly to speed, so when idling, a couple of amps is all you'll get, therefore when you have your lights on at idle, it will drop into negative on your meter as it isn't producing enough to totally power your lamps, it's using some power from the battery. When you rev, it produces enough to power your lights, and some extra which goes to replenish your battery. Turn your lights off and measure your battery volts in DC after running the tractor for 5 minutes at high revs.

 

[torch]

According to the WSM:

"AC dynamo produces higher voltage in slow speed rotation, compared with DC generator, and charges electric current to the battery during engine idling. Accordingly, there is no fear of battery failure."

So, with the lights off, check the battery voltage at idle. It should be higher than the battery voltage with the engine off.

 

[Eise]

Be very careful with AMP gauges....depending on the type, the though type must have all the current through it - thus a large gauge wire, shunt types and others are different.

YOUR machine has a DYNO - it when close to WOT will produce something close to 30 volts .....AC!

Once it goes through the regulator - stepped down to a normal 14 ish volt and gets converted to DC.

As for the Dyno - there are permanent magnets and of course the coil, which if not mistaken is one close loop making up 8 poles.

Here is a picture of the "guts" - this is one that the two sets of bearings decided to take a little permanent vacation!!!

I am pretty sure I've got the amp meter correctly connected, the wire that went from the starter to the ignition switch is connected to one side of the gauge, the ignition switch and alternator are connected to the other side. The new wiring that has been done with 10mm2 wire (about 7 gauge) just to be on the safe side.

I'll see if I get around to doing another measurement of the AC output at WOT, I thought it was just below 30volts AC, maybe 28.

 

[twomany]

I am pretty sure I've got the amp meter correctly connected, the wire that went from the starter to the ignition switch is connected to one side of the gauge, the ignition switch and alternator are connected to the other side. The new wiring that has been done with 10mm2 wire (about 7 gauge) just to be on the safe side.

I'll see if I get around to doing another measurement of the AC output at WOT, I thought it was just below 30volts AC, maybe 28.

Be sure to check output at high idle as well,
That is were the dynamo is designed to operate.

 

[Eise]

According to the WSM:

"AC dynamo produces higher voltage in slow speed rotation, compared with DC generator, and charges electric current to the battery during engine idling. Accordingly, there is no fear of battery failure."

So, with the lights off, check the battery voltage at idle. It should be higher than the battery voltage with the engine off.

The battery voltage at idle is the same, about 12.8 volts only if I revv it up (beyond what I would call idle) does it increase.

Be sure to check output at high idle as well,
That is were the dynamo is designed to operate.

At idle it's making about 8-9 volts AC, increasing the revvs slightly only raises the voltage to maybe 10-12 volts AC depending how high I let it idle. I'm pretty sure it's not charging at idle.. I have a feeling the regulator isn't receiving a high enough voltage at idle, either that or the regulator isn't working like it should.

What do you guys think, is it the dynamo or regulator that I should be looking at?

 

[85Hokie]

The battery voltage at idle is the same, about 12.8 volts only if I revv it up (beyond what I would call idle) does it increase.



At idle it's making about 8-9 volts AC, increasing the revvs slightly only raises the voltage to maybe 10-12 volts AC depending how high I let it idle. I'm pretty sure it's not charging at idle.. I have a feeling the regulator isn't receiving a high enough voltage at idle, either that or the regulator isn't working like it should.

What do you guys think, is it the dynamo or regulator that I should be looking at?

Based on what you are saying, I would say that your system is working well.
I have a digital voltmeter on my 92 B7100 and is fairly accurate based of comparing it to a VOM. - and at idle I get about zero plus volts, or no increase in volts.As I increase speed, the voltage goes up proportional to the speed of the engine. At normal grass cutting speed, it shows about 14.2 or so volts, at WOT it hits 14.4 -14.5 volts.

The dyno is almost foolproof - as long as you have a closed circuit and a permanent magnetic field, there will be voltage produced when spun Now - there could be a poor connection along the pathway to the regulator and or internal parts of the regulator could be crapping out.

Make sure the belt is tight too - and make sure IF you tighten the belt......loosen the bolt on the pulley first!

 

[Eise]

Based on what you are saying, I would say that your system is working well.
I have a digital voltmeter on my 92 B7100 and is fairly accurate based of comparing it to a VOM. - and at idle I get about zero plus volts, or no increase in volts.As I increase speed, the voltage goes up proportional to the speed of the engine. At normal grass cutting speed, it shows about 14.2 or so volts, at WOT it hits 14.4 -14.5 volts.

The dyno is almost foolproof - as long as you have a closed circuit and a permanent magnetic field, there will be voltage produced when spun Now - there could be a poor connection along the pathway to the regulator and or internal parts of the regulator could be crapping out.

Make sure the belt is tight too - and make sure IF you tighten the belt......loosen the bolt on the pulley first!

If what you're saying is right, am I correct in saying it's not supposed to charge the battery at idle? That still seems strange to me, why would they design it like that?

 

[85Hokie]

If what you're saying is right, am I correct in saying it's not supposed to charge the battery at idle? That still seems strange to me, why would they design it like that?

I agree - a little strange, but just going on what I see on mine

Many older alternators would not charge at idle - it had to be "excited" or fooled into being excited via a small bulb to make it charge at idle.

Get a small cheap voltage meter - I used this one and it was simple to hook up and very accurate.

https://www.amazon.com/4-0-30v-Digi...pID=41K0OIDN9pL&preST=_SY300_QL70_&dpSrc=srch

 

[baronetm]

I am installing some gauges and I just put in a amp-gauge and when the tractor is running at idle with the lights on the needle dips to the negative side and stays there until I rev it up. I have an older type B7100 with the alternator behind the fan, it's the two wire type. When I measure the output it reads 8 volts AC at idle, this seems low to me, does anyone know what the AC output voltage should be at idle?

Here is a link to B7100HST WSM another member posted recently, hope it matches your tractor and helps to clear up or answer some of your questions.

http://kubotabooks.com/AutoIndex/ind...M_complete.pdf

 

[Dave_eng]

I am pretty sure I've got the amp meter correctly connected, the wire that went from the starter to the ignition switch is connected to one side of the gauge, the ignition switch and alternator are connected to the other side. The new wiring that has been done with 10mm2 wire (about 7 gauge) just to be on the safe side.

I'll see if I get around to doing another measurement of the AC output at WOT, I thought it was just below 30volts AC, maybe 28.

The first test should be the one you mention which is AC voltage of the Dynamo at full engine speed. This test needs to be done with the wires from the dynamo disconnected.

Waste of time trying to measure amps with a dynamo and thristor regulator. On a good day max output is 10 amps DC.

If the AC voltage is 30 + and the DC voltage at the battery is not around 14 with a reasonable battery in place, then the rectifier is done.

Far better to monitor voltage with one of these LED displays. Less than $10 and simple to install

https://www.ebay.com/itm/DC-12V-24V...ltmeter/201948653697?var=&hash=item2f0513e881
Dave