Non-charging charging system

tack

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Kubota B1750 with FEL
Mar 16, 2021
12
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Norman Oklahoma
Greetings all; I'm trying to help my father-in-law with his Kubota B1750. I ran across this most excellent website, and I thought maybe someone coul;d help us. This tractor has the two-wire permanent magnet dynamo, and a six-wire regulator/rectifier assy. It wouldn't charge the battery. Being electricians, but not tractor electricians, and shade-tree mechanics at times, we naturally :oops: assume the dynamo has bellied up. So I order one from amazon (I know I should've tested the old one 🙄) installed new dynamo, but no worky. Dug around in the thing and found a regulator! So I ordered a regulator. Installed it today, figured this would do it . . . .🤯 🤬 No worky. Dynamo is outputting at idle 16.3VAc and we're getting a nice steady 11.93vdc at the battery. No good. If I have to I'll trace every wire leaving the regulator, but I reckon this must've been encountered before by many people, and I'm humbly (wifey may dispute this) coming in here with hat-in-hand hoping for some help to make this a lot easier. 🙏
 

Captain13

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M7040 4WD ROPS, ZD28
Feb 27, 2019
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Kathleen, GA
Check your grounds. Voltage at the battery should be about 12.6 so you have a voltage drop somewhere. I assume the battery has been checked and is ok? Also, clean the battery connectors.
 
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GreensvilleJay

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BX23-S
Apr 2, 2019
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have you checked the battery OUT of the tractor ( on the bench) properly ?
will a regular battery charger charge it ??
what's the terminal voltage ?
how many amps is the dynamo outputting to battery ?
does it pass a 'load test' ?
do you have a 2nd 'known good' battery to put into tractor ?
idle is not a good speed for testing, check manual bet it says med-hi speed ?
 

Dave_eng

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M7040, Nuffield 465
Oct 6, 2012
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Forum member Lugbolt has provided the following procedure for non charging dynamo systems. Let me start by saying rarely is the dynamo the problem.

Dave

Lugbolt's own tests

the regulator/rectifier has 6 wires. 2 are the same color, they end up at the dynamo. AC. One is a black ground wire. You will also have a +12v from the slow-blow fuse, and a +12v ignition (key on) and then a wire that runs to a charge lamp (if applicable, but it'll still have that wire).

Typically loss of charging performance is fairly easy to diagnose if you have the know-how, and a digital volt-ohm meter that has any quality whatsoever. A $10 one isn't that, just something else to throw into file 13 when it reads wrong.

The two dynamo wires (usually sky blue) are AC voltage, as said. Start engine, disconnect regulator and test ac output at the regulator connector, between the two dynamo wires. Should be 24V+ and I like to see more than 45 or so at full throttle. If it charges anything it's probably ok, they are a foolproof and extremely simple design that rarely fails outside of seized bearings. OK? Move on. Check your ground at the reg connector. One probe of the DVOM (set to ohms) on the ground pin in the connector and the other pin on a good ground, frame, transmission, etc. Must be clean. If you have more than a few ohms of resistance, your ground or harness is suspect

onward. Find your wire that comes from the battery. Backprobe the regulator connector. Now put your DVOM on DC volts. One probe goes to your connector, the other goes to the battery +. Should be under 500mv, or 0.500v. Ok? Move on. More than 0.5v? You have either a harness problem or a bad connection at the fuse, or whatever.

Last wire that will affect charging is what I call the "trigger" wire...it turns the reguator "on" so to speak, via the key switch. That one gets 12v when the key is on. Same as the last test, backprobe the connector with the key on. One probe of the DVOM in the connector and the other to the + battery terminal (use the post not the cable). You want to see less than 0.5v on the meter. If you see more than that, harness, fuse block, keyswitch, etc. Follow your wiring diagram. If you do see less than 0.5v, that circuit is not suspect, and there's a possibity you have a bad regulator.

Ideally you want to test everything AROUND the regulator because testing the reg itself isn't always conclusive. Thus, once you know you have AC voltage from the dynamo, you have good ground, you have +12v from the batt and ignition switch, the only component left is the reg. Process of elimination.

Electrical diag is not all that hard or it can be. It's all what you make of it. Don't put too much thought into it because it'll bite you. It's simple for the most part

speaking of being bit, be careful around the dynamo wires when testing. There's a little bit of voltage there and it's ac voltage, so it can bite you.
 
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tack

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Kubota B1750 with FEL
Mar 16, 2021
12
3
3
Norman Oklahoma
have you checked the battery OUT of the tractor ( on the bench) properly ?
will a regular battery charger charge it ??
what's the terminal voltage ?
how many amps is the dynamo outputting to battery ?
does it pass a 'load test' ?
do you have a 2nd 'known good' battery to put into tractor ?
idle is not a good speed for testing, check manual bet it says med-hi speed ?
Thanks for the reply. I happen to have had a battery load tester in the truck tool box. The battery tested quite good, but it's only ten months old and my father in law had it fully charged about three days ago when he first started working with it. Probably needs recharging, as evidenced by the low voltage now. 16.3vac at idle, voltage rose quickly into the twenties with a little throttle, the Dynamo is good. I read elsewhere on the forum that the dynamo rarely fails. With the old regulator, the charge light was brightly lit. With the new regulator, no charge light. I noticed that at first, battery voltage was 11.7 but it rose to a steady 11.93 after a few minutes, and remains steady regardless of RPMs. Sounds kinda like a voltage drop in series with the charge circuit doesn't it...........
 

tack

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Kubota B1750 with FEL
Mar 16, 2021
12
3
3
Norman Oklahoma
Forum member Lugbolt has provided the following procedure for non charging dynamo systems. Let me start by saying rarely is the dynamo the problem.

Dave

Lugbolt's own tests

the regulator/rectifier has 6 wires. 2 are the same color, they end up at the dynamo. AC. One is a black ground wire. You will also have a +12v from the slow-blow fuse, and a +12v ignition (key on) and then a wire that runs to a charge lamp (if applicable, but it'll still have that wire).

Typically loss of charging performance is fairly easy to diagnose if you have the know-how, and a digital volt-ohm meter that has any quality whatsoever. A $10 one isn't that, just something else to throw into file 13 when it reads wrong.

The two dynamo wires (usually sky blue) are AC voltage, as said. Start engine, disconnect regulator and test ac output at the regulator connector, between the two dynamo wires. Should be 24V+ and I like to see more than 45 or so at full throttle. If it charges anything it's probably ok, they are a foolproof and extremely simple design that rarely fails outside of seized bearings. OK? Move on. Check your ground at the reg connector. One probe of the DVOM (set to ohms) on the ground pin in the connector and the other pin on a good ground, frame, transmission, etc. Must be clean. If you have more than a few ohms of resistance, your ground or harness is suspect

onward. Find your wire that comes from the battery. Backprobe the regulator connector. Now put your DVOM on DC volts. One probe goes to your connector, the other goes to the battery +. Should be under 500mv, or 0.500v. Ok? Move on. More than 0.5v? You have either a harness problem or a bad connection at the fuse, or whatever.

Last wire that will affect charging is what I call the "trigger" wire...it turns the reguator "on" so to speak, via the key switch. That one gets 12v when the key is on. Same as the last test, backprobe the connector with the key on. One probe of the DVOM in the connector and the other to the + battery terminal (use the post not the cable). You want to see less than 0.5v on the meter. If you see more than that, harness, fuse block, keyswitch, etc. Follow your wiring diagram. If you do see less than 0.5v, that circuit is not suspect, and there's a possibity you have a bad regulator.

Ideally you want to test everything AROUND the regulator because testing the reg itself isn't always conclusive. Thus, once you know you have AC voltage from the dynamo, you have good ground, you have +12v from the batt and ignition switch, the only component left is the reg. Process of elimination.

Electrical diag is not all that hard or it can be. It's all what you make of it. Don't put too much thought into it because it'll bite you. It's simple for the most part

speaking of being bit, be careful around the dynamo wires when testing. There's a little bit of voltage there and it's ac voltage, so it can bite you.
Thanks Dave for the info from Lugbolt. That will save me some time. It looks like the problem is going to be a voltage drop in the charging circuit like the ground or the "trigger" to the regulator. Before the regulator was changed, the charge light was on. Now it's not. The old regulator I think was bad, but there's more than one problem.
 

tack

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Kubota B1750 with FEL
Mar 16, 2021
12
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3
Norman Oklahoma
Well we investigated the wiring, checked out the switch, grounds . . . . .All's good. The regulator brings the battery voltage "up" to 11.92v. The "Charge" light was on with the old regulator, with this new one the light stays off. I believe the regulator is factory defective, but my father-in-law doesn't want to send it back. The battery charges enough to start the engine, so he's happy.
 

lugbolt

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ZG127S-54
Oct 15, 2015
2,775
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Mid, South, USA
I'd certainly find the cause of undercharging. If left alone, there's possibility that a wire isn't passing enough current, potential for overheated wire--and with you being an electrician, you know what that can lead do.

the older tractors like you have had some issues with wiring--and key switches. Kind of a poor setup but it is what it is all we can do is deal with it-unless you want to reengineer it all.
 
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tack

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Kubota B1750 with FEL
Mar 16, 2021
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Norman Oklahoma
Well, my father-in-law decided to sell this tractor, so I bought it :p Now it's problems are all mine. I ordered a new ignition switch. I also have to repair corroded connections on a major wiring harness connector. I ordered a shop manual from ebay. But, I'm wondering about the rear lights, of which this tractor has none. I figure I could install some aftermarket pedestal lights on it, but could someone please tell me what's normally on there? Thanks a lot!

P.S. should I start a new thread on this?
 
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Dave_eng

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M7040, Nuffield 465
Oct 6, 2012
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Well, my father-in-law decided to sell this tractor, so I bought it :p Now it's problems are all mine. I ordered a new ignition switch. I also have to repair corroded connections on a major wiring harness connector. I ordered a shop manual from ebay. But, I'm wondering about the rear lights, of which this tractor has none. I figure I could install some aftermarket pedestal lights on it, but could someone please tell me what's normally on there? Thanks a lot!

P.S. should I start a new thread on this?
For me a new thread would be far less confusing and more members are apt to have advice without having to read a long story.

Dave
 
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GreensvilleJay

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BX23-S
Apr 2, 2019
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11.92 isn't 'up to charge'. I suspect a bad cell in the battery. Easy test, remove, put on bench, use regular 'battery charger'. When done, it should be at least 13.2-13.7 after an hour of sitting.
 
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tack

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Kubota B1750 with FEL
Mar 16, 2021
12
3
3
Norman Oklahoma
Thanks for the reply. I started a new thread.

The battery has a date on it; 5-20 so it's 12 months old. I charged it up and it holds a full charge. I replaced the regulator, but I'm going to run some tests on it. From ground to the red wire on the regulator, I read 44VDC! I've read that one cannot trust the published wiring diagrams, but this read wire is supposed to lead to hot "buss", leading to engine stop timer, combination switch, and eventually to the fusible link & battery. I know that some voltage regulators will read high with no load & feedback, so since being this wire should be a straight shot to the battery, I'm going to assume it's broken someplace. I'll report back what I find . . . . .
 

tack

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Kubota B1750 with FEL
Mar 16, 2021
12
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3
Norman Oklahoma
If anyone would like to know, the problem was in a large 8-pin quick-disconnect harness connector. the Red wire was broken in the connector due to corrosion. Earlier in past days working on this, i used to get a charge light. It was making contact a little, enough to enable the light but it was dropping a lot of voltage. I noticed the charge light no longer came on. The wire had had enough and broke all the way. other wired in this connector have problems too, so I'm going to replace the entire connector.
 
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tack

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Kubota B1750 with FEL
Mar 16, 2021
12
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Norman Oklahoma
If someone needs connectors, try a search on Amazon with these terms: "Glarks 400Pcs 6.3mm 1 2 3 4 6 8 9 Pin Electrical Automotive Wire Connector Male Female Socket Plug and Pin Header Crimp Wire Terminals Kit" This has an assortment, including the 8-pin connector. You can also order one type, but I didn't see any need to get 100 . . . . .
 

Mark_BX25D

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Bx25D
Jul 19, 2020
201
100
43
Virginia
If anyone would like to know, the problem was in a large 8-pin quick-disconnect harness connector. the Red wire was broken in the connector due to corrosion. Earlier in past days working on this, i used to get a charge light. It was making contact a little, enough to enable the light but it was dropping a lot of voltage.

This is why it's good to use a meter AND a test light. Poor connections may show the correct voltage when tested with a meter, but show their true colors when a load it put on them with a test light.
 
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tack

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Kubota B1750 with FEL
Mar 16, 2021
12
3
3
Norman Oklahoma
This is why it's good to use a meter AND a test light. Poor connections may show the correct voltage when tested with a meter, but show their true colors when a load it put on them with a test light.
Yeah, you're right. That's a problem with modern digital multimeters; they have an input impedance of 9-11megohms and don't load the circuit at all.
 

Mark_BX25D

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Bx25D
Jul 19, 2020
201
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43
Virginia
Yeah, you're right. That's a problem with modern digital multimeters; they have an input impedance of 9-11megohms and don't load the circuit at all.

Heh. Yeah, I learned that lesson the hard way back in my two-way radio days. Three call-backs before the light dawned and I grabbed a test light and figured out the problem.
 

tack

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Kubota B1750 with FEL
Mar 16, 2021
12
3
3
Norman Oklahoma
Well, it charges the battery fine finally. Now I'm going to work on the lights. the light switch was frozen, and prices for a new one are scary. I'm going to try lED lights in it too and see how that works out. The plastic reflectors in the headlight assemblies show sighs of getting hot and warping some.
 
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lugbolt

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ZG127S-54
Oct 15, 2015
2,775
275
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Mid, South, USA
This is why it's good to use a meter AND a test light. Poor connections may show the correct voltage when tested with a meter, but show their true colors when a load it put on them with a test light.
no that's what a voltage drop test is for. I've explained it here a couple times. Google it if you're not familar. It pinpoints voltage drops through conductors. Much more conclusive than even a test light. Plus if you don't have a test light you don't have to go buy yet another tool. I live in the sticks so running into town every time I need something is VERY inconvenient. And expensive.

I just did a repair on a scag for a friend. It was overcharging the battery (18v+). So the non tech way of doing this is to replace the regulator, right? Well wait, as said in a previous post, the regulator has a sensing wire, that senses the voltage and the reg will adjust voltage accordingly. This wire is normally triggered via the ignition circuit (switched +12v). So on mine, using a voltmeter I found that ground was 0.1v drop from the ground terminal to the earth post on the battery. Then I found that AC output was 34v at 2600 RPM (which is good). The battery (charging) wire had a drop of 0.09v. That eliminates 5 of the 6 wires on the regulator connector. The trigger, or sensing wire, was showing 4.77v drop between the terminal and the battery +. With that known, I knew that the regulator was "seeing" low voltage and attempting to charge at a higher voltage. Using the drop test, I found a connector in the harness that was showing a 8.5v drop across the connector. Depinned it, replaced the pins, then reassembled--now charges 14.05v at 3400 RPM which is perfect.

So in my case the drop test not only eliminated having to charge a customer $200 for a new voltage regulator (OEM of course) , it also saved me a TON of time in diagnosis, and it was a more accurate diagnosis. That entire repair took under 1 hours' time including the time it took to drop test, remove the regulator to gain access to it's connector, everything. Everyone wins and most importantly the owner of the equipment. Good video below explains the drop test and you'll see why it's important.