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Mexican Gerbil

Voltage Spike

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Many years ago I bought a high ampage alternator to run the spots and radio as the original really struggled. Any way all was good until one day the voltaged spiked and then lost all volts and was running on battery power only.

Was sent away to be fixed as hadn't had it long. Was returned and all good.

Fast forward 5 years and it's now fitted on the Mex. Been running it for 2 years. Last year it spiked again  but voltage returned to normal. 

Yesterday coming back from CF show it spiked about a dozen times, peaking at 18.1 volts. Fluctuating between normal 13.7 and 14 and 15 volts most of the time. 

We lost fuse 1 and one point which runs all my internal items (radio, map light, spots via relay and cig lighter) internal light and hazard. 

Do I have a short somewhere or is it the alternator? Last time I had earth issues the voltage dropped rather than spiked. 

Any ideas before a fork out on a new alternator 

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Sounds like a voltage regulator issue on the alternator itself. Be careful about any sustained running at those voltages, I would get it changed immediately. Even if you swap it out for a smaller output one you have lying around as a test measure. 

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Hi,

 

I would suspect 99%, that it will be a problem with the internal regulator in the alternator, any external problems in the electrical system is ,as you say, more than likely give the symptom of a voltage drop NOT spike, a spike like what you are getting at 18v could do a lot of harm to electronic items such as radios, and electronic ignition modules and such like, make sure that there is a good earth connection onto the engine block and the alternator bracket its self, the alternator needs a good return path on it.  

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Thinking a bit sideways here - regulator I agree with - easy enough to change to rule out or otherwise. But the spiking thing and the loss of that particular fuse could be connected . . . . . if there was a short - not enough to blow the fuse but enough current drawn so the alt. ramps up the output to compensate then with some vibration the short goes away and voltage / amperage drops away - repeat ad infinitum? Not a fan of volts gauges - ammeter far more useful for spotting failing alt. short circuits, excessive loads etc.

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I will get the one out of my estate and test the systems. 

I have a fluke amp meter so will put that on before the swap. 

That first time it happened many years ago it did damage the radio. I have separate fuses in an internal fuse box for the 4 items I mentioned above. 

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4 hours ago, Mexican Gerbil said:

I will get the one out of my estate and test the systems. 

I have a fluke amp meter so will put that on before the swap. 

That first time it happened many years ago it did damage the radio. I have separate fuses in an internal fuse box for the 4 items I mentioned above. 

Check the fuse rating on your Fluke on your current line. It might only be 10 amp max. 

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Now then. The meter wont register any amps....? Do I need to measure this at the alternator?

No spikes as yet soooooo.... pass

The earth strap comes off the alternator bracket and onto the cross member/chassis bolt. 

Seem to be getting a good earth there

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33 minutes ago, Mexican Gerbil said:

Now then. The meter wont register any amps....? Do I need to measure this at the alternator?

No spikes as yet soooooo.... pass

The earth strap comes off the alternator bracket and onto the cross member/chassis bolt. 

Seem to be getting a good earth there

You don't measure current in the same way as voltage. The meter needs to be in series with the Circuit being measured rather than across the positive and negative like when you're measuring voltage. 

See here

 

 

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10 minutes ago, Vista said:

You don't measure current in the same way as voltage. The meter needs to be in series with the Circuit being measured rather than across the positive and negative like when you're measuring voltage. 

Knew I should have paid more attention in electrical engineering at college....

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Ok. Meter only had a 10amp setting . 

But the voltage spiked when I started this time. And stayed high as the revs were high. Would this suggest the regulator is faulty as the voltage dropped when the revs dropped. 

 

Will fit spare alternator tomorrow as mrs gerbil wants me home for dinner

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2 hours ago, Mexican Gerbil said:

Now then. The meter wont register any amps....? Do I need to measure this at the alternator?

No spikes as yet soooooo.... pass

The earth strap comes off the alternator bracket and onto the cross member/chassis bolt. 

Seem to be getting a good earth there

If you have a Fluke multimeter, the first thing you need to do is test the 10A fuse, as you might have blown it now. 

Set the meter to Ohms and put your red probe in the 10A socket. If it stays on OL (open load) then it's blown. 

If it's OK, plug your red probe into the 10A socket. Set the dial to Amps and press the yellow button for DC current. 

Any current testing must be done with the red and black probes now in series. If you were testing the current on a particular fuse line or looking for a parasitic drain, then this means you would have to pull the fuse and put the red probe on one side of the fuse housing and the black on the other (see pic for example). This setting is normally good for single fuse lines. 

If you were looking for current being drawn from a battery (engine not running), then you would need to disconnect either battery cable (positive or negative) and again connect the meter probes in series. One probe on battery post and the other on battery lead. This is normally how you find an overnight drain (parasitic/quecant drain). 

However, only having a 10A fuse on your meter, I would be very reluctant to look for any current coming out of your alternator, as it will likely blow if your regulator isn't working. Much better to use a DC clamp meter. This is normally done for testing cranking current draw. 

To be honest, you don't need to check the current really. Better off just measuring the voltage across the battery. A decent alternator will put about 13.8V across a battery when running and up to a maximum of about 14.5 to 14.7V if under heavy load, just after starting with ancillarys switched on. The more you switch on the more it will pull, but should then regulate at around 14.5V.

If your meter, across the battery is kicking out more volts than that when running, then your regulator is stuffed. On your car, there shouldn't really be anything capable of hitting the line with a transient spike when switching something off, as it's all old school electrics. 

Hope this makes a bit of sense and helps out. 👍

IMG_20190604_204436892.jpg

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21 hours ago, dt36 said:

If you have a Fluke multimeter, the first thing you need to do is test the 10A fuse, as you might have blown it now. 

Set the meter to Ohms and put your red probe in the 10A socket. If it stays on OL (open load) then it's blown. 

IMG_20190604_204436892.jpg

 

 

Thanks for the help. I got a 0.L so must have blown the fuse.

 

Swapped the alternator out of my 1300 Estate, which looks like an original Lucas one (tick in the concourse box)

Ran the same scenarios as yesterday and the most I got out of it was 14.1 Volts. No Spikes.

Will look at getting the other 2 alternators sorted before the tour...... don't want any other mishaps this year.

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1 hour ago, Mexican Gerbil said:

Thanks for the help. I got a 0.L so must have blown the fuse.

 

Swapped the alternator out of my 1300 Estate, which looks like an original Lucas one (tick in the concourse box)

Ran the same scenarios as yesterday and the most I got out of it was 14.1 Volts. No Spikes.

Will look at getting the other 2 alternators sorted before the tour...... don't want any other mishaps this year.

Haha, I had an inkling it might be. No worries though as they are fairly easy to replace. However, not the cheapest, speaking from experience. I assure you, I can let the smoke out of anything 😁

The fuse you'll need will be 11A, 1000v. They can actually take about 20A for a very short period, but any more than that or longer and their toast. I've recently bought a new 400A ac/dc clamp meter in work from RS for this very reason. 

Have a look below for the fuse. You can get cheaper generics though on eBay, but I'm not sure what quality they are:

https://uk.rs-online.com/web/c/test-measurement/multimeters-accessories/multimeter-fuses/

 

 

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