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Old 11-22-2017, 05:06 PM   #1
swedish-rocket
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Default Alternator/charging

I'm trying to fix my charging system. At idle I'll get 13.8 volts once I start turning on my lights, switches, radio etc. it drops voltage. I got it to drop under 11 volts this way. Is there anything I can check?
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Old 11-22-2017, 07:02 PM   #2
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Assuming this is on an older Volvo with the older style alternator with the replaceable brushes. You can check those brushes.

You can and SHOULD also check the wires (especially the ground) as... if you look back through the threads I've started you can find the one where my car lit on fire on it's own in my driveway and damn near took out my whole neighborhood.
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Old 11-22-2017, 08:04 PM   #3
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It's a 1990 Volvo 240 with a internal regulator. Wow on your car. Glad no one got hurt. Sorry on your car loss though.
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Old 11-22-2017, 08:27 PM   #4
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My alternator wire burned up on a rainy summer day on the way home from work. Some day i will post the pictures of the carnage. It took out the ground and about a foot or so of the wiring harness. All the way to under the crank pulley from the alternator. I replaced the whole run with a 6 gauge wire from starter to alternator.
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Old 11-22-2017, 08:33 PM   #5
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In answer to your post. Yes, it does seem to be loading down the alternator just a bit more than it should. 13.8v is really the minimum you need for the modern batteries. So unloaded the system is at minimum allowable voltage. Maybe a new regulator. as well as brushes? It happens less often but a rectifier diode can fail and that will cause low voltage and low current output with an alternator.
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Old 11-22-2017, 08:34 PM   #6
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Did you check for slipping belt?
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Old 11-22-2017, 10:02 PM   #7
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Quote:
Originally Posted by swedish-rocket View Post
It's a 1990 Volvo 240 with a internal regulator. Wow on your car. Glad no one got hurt. Sorry on your car loss though.
Oh don't worry. I put it out. Keep a fire extinguisher in your car people! And I'm not talking about one clamped to your A pillar either lol

Quote:
Originally Posted by dl242gt View Post
My alternator wire burned up on a rainy summer day on the way home from work. Some day i will post the pictures of the carnage. It took out the ground and about a foot or so of the wiring harness. All the way to under the crank pulley from the alternator. I replaced the whole run with a 6 gauge wire from starter to alternator.
Yep same.
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Old 11-22-2017, 10:08 PM   #8
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First off, where are you measuring the voltage. If you are measuring the voltage at the alternator B+ terminal (battery connection) that is the correct place. Any other location and a bad electrical connection could be responsible for the drop in voltage that you are measuring, not the alternator. As you increase the current load the resistance in a bad connection causes a voltage drop proportional to current flow - hence reduced voltage at increased load. Bad electrical connections can cause heat which can cause the problems identified by others.

If you are measuring and seeing the voltage drop right at the alternator terminal, then you have one of the following
- a bad ground on the alternator (same problem as a bad connection) or
- a bad electrical connection within the alternator, perhaps the rectifier assembly
- the voltage regulator is failing to respond to the drop in voltage.

In the case of the regulator, as the load current increases on the alternator the internal impedances within the alternator cause the terminal voltage to drop. The regulator measures the output voltage and attempts to restore the output to the set point by increasing the voltage applied to the field winding which results in increased field current which boosts the alternator output voltage. On an external regulator alternator it is easy to test the operation of the regulator, not so easy on an internal regulator alternator. Failure to respond to the voltage drop could indicate a regulator problem. In a freak set of circumstances where the alternator has enough residual magnetism to generate some voltage at light load, it might also indicate a brush problem. Pulling the regulator / brush holder out to check for damaged brushes is relatively easy.

Go towards the bottom of the following page:

http://www.240turbo.com/AdjustableVoltage.html

Dave Barton provides a lot of useful information on testing your alternator.
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Old 11-22-2017, 11:50 PM   #9
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Thanks guys! I checked it at the battery terminals and cigarette lighter. It will be kind of hard but doable at the terminals. I was hoping for bad ground but maybe there is a issue with the regulator. I'll check these points soon.

Awesome info again! Thanks!
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Old 11-23-2017, 08:40 AM   #10
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Quote:
Originally Posted by EivlEvo View Post
Oh don't worry. I put it out. Keep a fire extinguisher in your car people! And I'm not talking about one clamped to your A pillar either lol
.
I really need to get a fire extinguisher!
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Old 11-23-2017, 03:13 PM   #11
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Quote:
Originally Posted by swedish-rocket View Post
Thanks guys! I checked it at the battery terminals and cigarette lighter. It will be kind of hard but doable at the terminals. I was hoping for bad ground but maybe there is a issue with the regulator. I'll check these points soon.

Awesome info again! Thanks!
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Old 11-24-2017, 12:23 PM   #12
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I see a new purchase in the near future. I found I had a older bosch alternator in storage. I installed it and the same thing happened. I have 4 gauge wire to the motor from the alternator. I hooked a battery ground to the alternator battery with a 8ga wire. I may run a wire directly from the + power terminal of the battery to alternator to see if that will correct it. I can't seem to get measure the positive wire on the alternator to ground. Maybe I'll try again later.

Btw I brought both alternators to autozone and they both passed the bench test.
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Old 11-24-2017, 05:01 PM   #13
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Added a ground wire and added a positive wire directly from the battery to alternator. Same voltage drop.
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Old 11-24-2017, 06:23 PM   #14
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The alternator tested good? What were the specs? What current draw are the accessory items that you are running? If you have a high power stereo that alone can cause what you are seeing. The alternator can only supply so much current and if your draw is more than it can handle you go below charge voltage for the battery and have low voltage throughout the system.

Last edited by dl242gt; 11-24-2017 at 06:23 PM.. Reason: change word
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Old 11-24-2017, 06:33 PM   #15
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All it takes is the headlights and the blower motor to drop the voltage down under 12 volts. I have 340LPH pump but it's not affecting it. The stereo is currently one 5" speaker and a CD player.

I believe both are 80 amp alternators.

No specs were given. Autozone is pass fail machine.

Last edited by swedish-rocket; 11-24-2017 at 06:46 PM..
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Old 11-24-2017, 08:15 PM   #16
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Hmm, the machines usually will test voltage at rated current. So if they are good then something on the car isn't. I would check out the basic power wiring layout. Make sure feeds to the fuse box and dash are all good and clean. They come from the power distribution on the inner left fender. that gets power from a smaller red wire from the positive on the battery. Also the grounding path between engine, body, and battery needs to have a good low resistance path.

When you connect the alternator are you connecting the small red wire to D+? there should be a case ground to the bracket on the engine. The big red goes to B+. some alternators have both a D+, and a D- on the back. D+ is the proper connection for the small red wire. Keep at it, sometimes these electrical issues are more than one bad connection or problem.
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Old 11-24-2017, 08:18 PM   #17
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Maybe try doing voltage drop tests of the cables. Look up what a voltage drop test actually entails. I do it all the time for intermittent no cranks on trucks.
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Old 11-24-2017, 11:12 PM   #18
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Quote:
Originally Posted by dl242gt View Post
Hmm, the machines usually will test voltage at rated current. So if they are good then something on the car isn't. I would check out the basic power wiring layout. Make sure feeds to the fuse box and dash are all good and clean. They come from the power distribution on the inner left fender. that gets power from a smaller red wire from the positive on the battery. Also the grounding path between engine, body, and battery needs to have a good low resistance path.

When you connect the alternator are you connecting the small red wire to D+? there should be a case ground to the bracket on the engine. The big red goes to B+. some alternators have both a D+, and a D- on the back. D+ is the proper connection for the small red wire. Keep at it, sometimes these electrical issues are more than one bad connection or problem.
I got the ground going from the alternator to block with 4ga wire. The small red wire is going to D+ 8mm head bolt. The B+ is coming from the starter I believe that then goes to the battery.
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Old 11-24-2017, 11:14 PM   #19
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Quote:
Originally Posted by ZVOLV View Post
Maybe try doing voltage drop tests of the cables. Look up what a voltage drop test actually entails. I do it all the time for intermittent no cranks on trucks.
I'll probably spend sometime figuring how to check components. I think I'm going to have spend a bit of time hunting this issue down. Thanks for all the info guys!
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Old 11-25-2017, 09:39 AM   #20
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142 covered it well..... but I saw no mention of amperage delivery. Alternators are not fixed output devices.... they charge what the system "needs". Right after a start cycle, the amperage will be peak to restore your battery.....

Low 14s is what you should see, as was mentioned. Grounds grounds grounds, will break your heart. Also, never trust a bolted together front clip for the ground path of those lights mounted thereupon.

Last - if your car came factory with 80A capacity, and you've upsized the fuel pump/stereo, why wouldn't you upgrade to 100A charging? Throw one of the Nippon Denso baby alternators on there......
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Old 11-25-2017, 10:56 AM   #21
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It's still dropping voltage just running the fuel pump which is on a separate 10ga wire and switched on with a relay. I've had two batteries and MTX1000D with 3 subwoofers in the car years ago with a large capacitor. It always worked well.
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Old 11-25-2017, 12:05 PM   #22
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How many millivolts voltage drop did you get on your cables!!!!?

For example, I measure from battery positive to an under hood fuse block positive on the trucks I work on, crank, no more than 200 mv should read on the meter. On the ground side I measure from battery negative to the furthest engine metal away from the battery, then crank, 200mv is the most I should see here too. If more, replace the cable.

I had another vehicle that was a no crank. From negative terminal at battery to chassis I was already reading 1.5 v without even trying to crank. When hitting crank, the meter went all the way up to 11.5v!!! NO ground!!!. Found the ground wire loose buried deep under fuse block, etc. Couldn't see it.


Ok point is, learn to do voltage drop testing. Look it up! It's a measure of millivolts, NOT how much your 12v is dropping down.

It may not be the cause, but these cars the crimps go bad on the cables and may look fine but will likely fail voltage drop tests!!!

Last edited by ZVOLV; 11-27-2017 at 08:38 PM..
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Old 11-25-2017, 03:32 PM   #23
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Had a similiar issue on my 240.

I crimped a new ring terminal onto the exciter wire when I switched from a Bosch to a Denso 100A. When the Denso started failing, I switched back to a Bosch. (Kept my old Bosch and put in a new voltage regulator).

When I put the Bosch back in, I was only getting 12.8 volts or so at the battery. I checked and had 12v at the exicter wire, so then went through all the usual diagnostic checks and cleaned all the grounds. Still only 12.8 at the battery. Double checked all the connections again. Turns out the ring terminal that I had crimped on for the Denso was too big, and not making a good connection with the Bosch.

Crimped a new, smaller connector and that solved it. 14.1V at the alternator (B+ to Ground), and 14.0 at the battery at idle.
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Old 11-26-2017, 03:19 PM   #24
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It maybe, today it ran 13.8v at the dash 13.2 when blower was on full 12.9 with head lights were on normal and 12.8 with the stereo was on. I took it to autozone and it passed the charging system test. I'll spend sometime in the near future testing.
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Old 11-26-2017, 03:26 PM   #25
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How old and low in charge was your battery?
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