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New alternator to car cause relay to buzz - can you help?

Wilf

Apr 5, 2014
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Good evening everyone. I have signed up to your forum as I have a problem with a new alternator that I have fitted to my car and just can't seem to find the answer from the auto electrician world. I'm hoping someone here has the answer.

I am an ex motor engineer with a basic knowledge of electronics. This is the problem.....
The alternator on my car stopped charging so I fitted a NEW one. I have done this many times in the past to new and old cars and have never experienced the problem this one has caused.

The new alternator had the exact same connectors as the old one and everything fitted perfectly. The car started and the volt meter on the dash and confirmed by a multi meter across each battery (it has two in paralell) read 14.3 volts. The problem is that when the ignition is on and the engine not running (alternator not turning) a relay in the engine bay fuse box buzzes. As soon as the engine is running the buzzing stops. It did not do this with the old alternator.This is what I have found out so far:

The function of the relay is to COMPARE the voltage from the battery to the voltage from the Alternator's OUTPUT lead. When the Alternator is HIGHER, the "coil" in the Relay [an electromagnet] moves the internal switch and connects the Alternator-output to the Battery - thus charging the battery.

The Relay is INTENDED to switch BACK [i.e. disconnect the battery from the alternator-output] when the voltage of the Alternator is BELOW that of the battery - thus saving the BATTERY from accidental discharge when the alternator IS NOT being driven by the engine [or becomes faulty!].

The relay is buzzing (switching on and off very quickly) because the voltage to it when the engine is not running is too low. I have not tested exactly what the voltage is with the ignition on and engine not running but have been told it is about 7.6v.

I have been told that new alternator may have been fitted transistorised rectifier/regulator which does not allow a constant milliamperes draw hence the fast on and off of the relay causing it to buzz.

Will it be possible for me to identify the rectifier and regulator in my old alternator so I can buy them and fit to it?
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Hi Wilf and welcome to Electronics Point :)

I don't know much about automotive electrical but I'll try to help. My first thought is that the voltage comparing relay is buzzing because it's rapidly alternating (no pun intended) between two states: first, it thinks that the alternator's output voltage is higher than the battery voltage, so it turns on the relay to connect them together, then second, with the alternator connected to the battery, it cannot be higher, so it turns the relay off. Then it detects that it is higher, and so on.

I think this COULD (grasping at straws here) be caused by the new alternator not having a path to ground when it's not running, and the circuitry inside the voltage comparing relay pulling that voltage up (probably only weakly). With no path to ground in the alternator, the actual alternator output voltage would be pulled up by the relay. Then when the relay closes and connects the alternator output to the battery, this will pull the voltage down, so the relay will open, and the cycle will repeat.

You can find out if this is happening pretty easily. Temporarily short the alternator's output to chassis, and see if that stops the relay from buzzing when you turn the ignition ON. If it does, you can make a permanent change by replacing the short circuit with a resistor. In other words, connect a resistor from the alternator output to ground.

I suggest you start with a 560 ohm, 1 watt resistor like this one: http://www.digikey.com/product-detail/en/ERG-1SJ561/P560W-1BK-ND/35927

You can probably find one locally. That reference is just to show you what sort of thing you're looking for. I've suggested a wirewound one, on the assumption that it would hold up better in an automotive environment (temperature, vibration etc). You don't need to worry about it burning out or needing to be fused; its own resistance will limit the current that can flow through it. Its effect on the alternator will be like a drop of water in a swimming pool.

If you have resistors on hand, you can try any 1W rated resistor of 470 ohms or higher, or any 0.5W rated resistor of 1k or higher. If the resistor value is too high, it may not load the rail down enough.

As for the rectifier/regulator, I can't say much about that. I think these are normally built into the alternator. It's certainly possible that the new alternator could have different circuitry in it, and that this would cause the problem if the relay pulls the voltage up as I've described.

Good luck!
 

duke37

Jan 9, 2011
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The alternator will have diodes in it which will allow charging but not discharging. The main output connection will be direct to the battery so could give a massive curent if you do not treat it right.
The alternator seems to work OK at 14.3V so why worry?

There is an auxilliary lead to energise the alternator and show the charging light on start up. I assume this is taking current when the ignition is on, try disconnecting it. Does it still click?
What does the relay do? Does it isolate some auxilliaries until the alternator is up to voltage?
 

Wilf

Apr 5, 2014
5
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Hi Wilf and welcome to Electronics Point :)

I don't know much about automotive electrical but I'll try to help. My first thought is that the voltage comparing relay is buzzing because it's rapidly alternating (no pun intended) between two states: first, it thinks that the alternator's output voltage is higher than the battery voltage, so it turns on the relay to connect them together, then second, with the alternator connected to the battery, it cannot be higher, so it turns the relay off. Then it detects that it is higher, and so on.

I think this COULD (grasping at straws here) be caused by the new alternator not having a path to ground when it's not running, and the circuitry inside the voltage comparing relay pulling that voltage up (probably only weakly). With no path to ground in the alternator, the actual alternator output voltage would be pulled up by the relay. Then when the relay closes and connects the alternator output to the battery, this will pull the voltage down, so the relay will open, and the cycle will repeat.

You can find out if this is happening pretty easily. Temporarily short the alternator's output to chassis, and see if that stops the relay from buzzing when you turn the ignition ON. If it does, you can make a permanent change by replacing the short circuit with a resistor. In other words, connect a resistor from the alternator output to ground.

I suggest you start with a 560 ohm, 1 watt resistor like this one: http://www.digikey.com/product-detail/en/ERG-1SJ561/P560W-1BK-ND/35927

You can probably find one locally. That reference is just to show you what sort of thing you're looking for. I've suggested a wirewound one, on the assumption that it would hold up better in an automotive environment (temperature, vibration etc). You don't need to worry about it burning out or needing to be fused; its own resistance will limit the current that can flow through it. Its effect on the alternator will be like a drop of water in a swimming pool.

If you have resistors on hand, you can try any 1W rated resistor of 470 ohms or higher, or any 0.5W rated resistor of 1k or higher. If the resistor value is too high, it may not load the rail down enough.

As for the rectifier/regulator, I can't say much about that. I think these are normally built into the alternator. It's certainly possible that the new alternator could have different circuitry in it, and that this would cause the problem if the relay pulls the voltage up as I've described.

Good luck!

Hello, thanks for your reply.

I was told that the relay is buzzing (rapidly switching on and off) because the voltage to it when the alternator is not turning is too low but your theory seems to make more sense.

You say “short the alternator’s output to chassis” – which lead is the correct one to short? There are two quite thick white cables that bolt to the rear of the alternator, I assume these take the power to the batteries. There is also a plug with two spade terminals, I think one goes to the battery light in the dash and I’m not sure what the other one does?

Yes the rectifier/regulator are built in but they can be bought and replaced. I did take my old alternator to and auto electrical repair shop, they seemed to think that the rectifier and regulator where at fault and needed replacing but they could not source the correct parts for my alternator. They were surprised that none of their suppliers could supply the correct parts. Hence I bought a new one.
 

Wilf

Apr 5, 2014
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The alternator will have diodes in it which will allow charging but not discharging. The main output connection will be direct to the battery so could give a massive curent if you do not treat it right.
The alternator seems to work OK at 14.3V so why worry?

There is an auxilliary lead to energise the alternator and show the charging light on start up. I assume this is taking current when the ignition is on, try disconnecting it. Does it still click?
What does the relay do? Does it isolate some auxilliaries until the alternator is up to voltage?

I would like to stop the buzzing as it is quite loud, also sometimes another relay under the dash stats buzzing too. It's not right and surely it will shorten the life of the relays.

You can see in the pictue below the wires and 2 terminal plug that connect to the back of the alternator. Which lead do I disconnect?

This is what I was told the relay does:- The function of the relay is to COMPARE the voltage from the battery to the voltage from the Alternator's OUTPUT lead. When the Alternator is HIGHER, the "coil" in the Relay [an electromagnet] moves the internal switch and connects the Alternator-output to the Battery - thus charging the battery.

This is what I am told the terminals of the relay are:
1 = From warning light
2 = Enables 4 wheel drive & fan
3 = Line into alternator
4 = +'ve from battery
5 = -'ve from battery

alternator_zps7493b4d1.jpg
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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You say “short the alternator’s output to chassis” – which lead is the correct one to short? There are two quite thick white cables that bolt to the rear of the alternator, I assume these take the power to the batteries. There is also a plug with two spade terminals, I think one goes to the battery light in the dash and I’m not sure what the other one does?
It looks like both of those white wires connect to the same screw. If so, that would be the output of the alternator. So that would be the point to short to chassis. Otherwise, I don't know.

Obviously, don't try to start the engine with the alternator shorted out! Just turn the ignition ON and see whether the relay buzzes or not.
 

duke37

Jan 9, 2011
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Be very careful about connecting anything to the alternator, if you connect to the main output, you are effectively connecting to the battery. Much heat and molten metal can result.

I think the explanation of how the relay works is not correct. This was the case when a dynamo was the generator but an alternator uses diodes in its output so the switch is not needed.
The relay you have seems to be what I suggested, a means of disconnecting auxilliaries until the alternator is producing a good voltage allowing full battery power for starting.

How many terminals does the alternator have?
Edit. This has been answered.
Those I have seen have a big terminal which is connected to the battery and possibly the starter also, then there is a smaller terminal which is connected to the ignition bulb to energise the alternator at start up. If the bulb has blown, the alternator may not start. Have you changed the bulb for a different rating? Is the bulb feeding the relay coil or is it switched by the relay.

Poor earths can cause all sorts of problems but I cannot think how this is the case here.
Has the old alternator been tested to see if it was faulty, if so, what was the fault?

I suggest you borrow a relay from your alternator supplier to check if yours is too sensitive.
 
Last edited:

Wilf

Apr 5, 2014
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Be very careful about connecting anything to the alternator, if you connect to the main output, you are effectively connecting to the battery. Much heat and molten metal can result.

I think the explanation of how the relay works is not correct. This was the case when a dynamo was the generator but an alternator uses diodes in its output so the switch is not needed.
The relay you have seems to be what I suggested, a means of disconnecting auxilliaries until the alternator is producing a good voltage allowing full battery power for starting.

How many terminals does the alternator have?
Edit. This has been answered.
Those I have seen have a big terminal which is connected to the battery and possibly the starter also, then there is a smaller terminal which is connected to the ignition bulb to energise the alternator at start up. If the bulb has blown, the alternator may not start. Have you changed the bulb for a different rating? Is the bulb feeding the relay coil or is it switched by the relay.

Poor earths can cause all sorts of problems but I cannot think how this is the case here.
Has the old alternator been tested to see if it was faulty, if so, what was the fault?

I suggest you borrow a relay from your alternator supplier to check if yours is too sensitive.

The buld has/had not blown. I have had the car for 3 years and never replaced it.

"Is the bulb feeding the relay coil or is it switched by the relay." I don't know for sure. I will see if I can find a wiring diagram for it.

When I replaced the alternator I removed, cleaned and treated the earth connections on chassis and engine although they were fine before doing so. I took the alternator to an auto electrical firm that specialise in reparing starter motors and alternators. They said it needed a new rectifier and regulator, whether they did some sort of test on these components or just saw the bearings and brushes were ok thought it must be those two components who knows.

I'll see if I can get a relay from a scrap yard as the alt. supplier would have to order one in probably at vast expense. I did a check on the relay, I removed it and powered it with a 3 cell lipo pack which was at 11.3v and it worked absolutly fine. Maybe what I was originally told about the voltage being to low is correct, I'll check it with a 2 cell lipo (nom. 7.4) later and if the 'LOW VOLTS' theory is correct it should buzz.

This is what led me to test the voltage across the battery in the first place and discover the alternator was not charging. I turned the ignition on the other day and the following happened. Up until then there had been no problem.

1. The ‘4 wheel drive’ light stayed on although it was dull. If you switch FWD in you hear it engage and the light goes bright (as it should).
2. The handbrake/warning light stayed on dull but handbrake was off, if you pull it on the light goes bright (as it should).
3. The ‘Battery’ light stays on dull.
4. The tiny green lights inset into the heater buttons do not illuminate and the heater fan does not come on.

The state of the above remaind the same when the engine was started.

Since fitting the new alternator these faults have all gone. I have noticed that the 'four wheel drive' dash light and the 'battery' light come on bright for a second or two when you switch the ignition on then go dim until the engine is started at which point they go out. I can't remember if this is normal and how it was before but I will endevour to find out.
 

Wilf

Apr 5, 2014
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Don't know if this means anything but I just removed the relay and powered it with 7.4v and it operated as normal with no buzzing. It just clicked in when the power was connected and out when disconnected. I then did the same test with 5.9v, it behaved exactly the same but the click when connected was not as strong which is what you would expect. At no time did is oscillate between ON and OFF at the low voltage.

I have taken a photo of the original alternator as I just spotted an ID tag on it and what looks like connection detail. Am I reading this wrong or does the symbol for 'L' and 'S', refer to the 'two spade' connector (I'm guessing LIVE and SWITCH) and the does the other earth (-'ve) symbol refer to the threaded terminal which is where those two thick white cables attached to?


alt-01_zps02dc0c25.jpg
 

elebish

Aug 16, 2013
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177
Good evening everyone. I have signed up to your forum as I have a problem with a new alternator that I have fitted to my car and just can't seem to find the answer from the auto electrician world. I'm hoping someone here has the answer.

I am an ex motor engineer with a basic knowledge of electronics. This is the problem.....
The alternator on my car stopped charging so I fitted a NEW one. I have done this many times in the past to new and old cars and have never experienced the problem this one has caused.

The new alternator had the exact same connectors as the old one and everything fitted perfectly. The car started and the volt meter on the dash and confirmed by a multi meter across each battery (it has two in paralell) read 14.3 volts. The problem is that when the ignition is on and the engine not running (alternator not turning) a relay in the engine bay fuse box buzzes. As soon as the engine is running the buzzing stops. It did not do this with the old alternator. This is what I have found out so far:

The function of the relay is to COMPARE the voltage from the battery to the voltage from the Alternator's OUTPUT lead. When the Alternator is HIGHER, the "coil" in the Relay [an electromagnet] moves the internal switch and connects the Alternator-output to the Battery - thus charging the battery.

The Relay is INTENDED to switch BACK [i.e. disconnect the battery from the alternator-output] when the voltage of the Alternator is BELOW that of the battery - thus saving the BATTERY from accidental discharge when the alternator IS NOT being driven by the engine [or becomes faulty!].

The relay is buzzing (switching on and off very quickly) because the voltage to it when the engine is not running is too low. I have not tested exactly what the voltage is with the ignition on and engine not running but have been told it is about 7.6v.

I have been told that new alternator may have been fitted transistorized rectifier/regulator which does not allow a constant milliamp draw hence the fast on and off of the relay causing it to buzz.

Will it be possible for me to identify the rectifier and regulator in my old alternator so I can buy them and fit to it?

Most car and truck alternators are 3 phase alternators with 2 diodes (for full wave rectification) in each phase. It is possible that one diode in one of the phases is shorted or open, probably shorted. I say this because the relay does not chatter when car is running but does when the ignition is turned on. That would be because the battery voltage is feeding back through the shorted diode and through the generator field winding, lowering the battery voltage to the point of being below what the relay needs to energize. The battery is always connected to the alternator positive output and to the starter contactor and the other small wires from the alternator runs to the regulator and to the "check bulbs circuit" to light the warning lights when the alternator is not putting out it's proper voltage necessary for charging the battery or when the battery is very low at engine start. The bulbs extinguish when there is little differential in the voltage between a normal full charged battery and alternator output (engine running). Note: A defective alternator output could read normal with little loading but low when headlights turn on. A scope will show fast changes in voltage during engine run but a voltmeter will not.
Ed.
 

duke37

Jan 9, 2011
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The big threaded terminal is the battery positive and the feed to the starter. Under no cercumstances should this be connected to earth. The frame of the alternator is the earth.

One of the smaller wire provides energising to get the alternator started. I assume the chattering relay is connected in this wire.
The relay is there to isolate thirsty ancilliaries until the alternator is producing output. The reason for the chattering is that it is energising something which drops the battery voltage so it isolates the device so the bsttery voltage rises etc etc etc. A steady voltage on the relay willl not show chattering.

Perhaps the field current in the two alternators is different giving the different reactions. A leaky regulator will drop the voltage at the small terminal so affecting the relay.
 

shrtrnd

Jan 15, 2010
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Are you sure the replacement alternator is an exact replacement?
Might it be an updated version with added features not intended for the original installation.
 
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