Alternators (I think?)

[Mark579]

Hi, I have a twin alternator set up (with a Merlin battery management system) to charge 1x110a starter and 3x110a domestic batteries. The alternators are sometimes charging (14.05ish volts on the multi-meter for both) and sometimes not (12.5 - 12.8ish volts for both). Any ideas on what would cause them both to stop charging while the engine is running? 

[Tony Brooks]

Very loose drive belts.

 

How discharged are your batteries. The higher the charging current the lower the charging voltage. On the basis of what you said I would suspect flat or faulty batteries if the belts are OK..

[Mark579]

Thanks Tony, currently at 78% on the domestic side according to smartguage (had the problem since Sunday night though), not sure on the starter battery because it's the supplementary. Belts are deffo not loose. Performance over the winter has suggested bthat the batteries were due for renewal soon. Was going to take the alternators off to a place near by for a freshen up, but if it's the batteries...well best dig me credit card out

[Tony Brooks]

11 minutes ago, Mark579 said:

Thanks Tony, currently at 78% on the domestic side according to smartguage (had the problem since Sunday night though), not sure on the starter battery because it's the supplementary. Belts are deffo not loose. Performance over the winter has suggested bthat the batteries were due for renewal soon. Was going to take the alternators off to a place near by for a freshen up, but if it's the batteries...well best dig me credit card out

I don't think that we can condemn the batteries without current and voltage readings for both banks.

 

In my view 78% charged should not allow sufficient current to flow to pull the charge voltage down.

 

As both alternators are likely to be of similar age I suppose the brushes may be worn and sometimes not making a good contact. Lucking you can get the regulator and brush holder off most alternators in situ to check them as long as you are careful. If they are worn check the sip rings for grooving.

 

[Mark579]

Voltage readings taken as 12.5+ on both starter and domestic before starting the engine then 14.05 on both when the engine was in idle. Then it cut out and went back to 12.5+ while the engine was running. Took the readings from the battery terminals because trying from the alternators gave mad fluctuations. I'm about armpit deep in terms of understanding at this point...?

[ditchcrawler]

So the voltage you took was after some gizmo to combine the two alternators.  If this is the case then you could be like someone posted a few months back with one alternator given up months ago and one doing all the work and has now started complaining.

Edited July 4, 2019 by ditchcrawler
spill chuck dont now moths from months

[Tony Brooks]

20 minutes ago, Mark579 said:

Voltage readings taken as 12.5+ on both starter and domestic before starting the engine then 14.05 on both when the engine was in idle. Then it cut out and went back to 12.5+ while the engine was running. Took the readings from the battery terminals because trying from the alternators gave mad fluctuations. I'm about armpit deep in terms of understanding at this point...?

I think brushes would be a fair suspect then.

 

See Brian's post.

Edited July 4, 2019 by Tony Brooks

[Mark579]

6 minutes ago, ditchcrawler said:

So the voltage you took was after some gizmo to combine the two alternators.  If this is the case then you could be like someone posted a few months back with one alternator given up months ago and one doing all the work and has now started complaining.

Yes but the relay has not connected, so I'm assuming the readings were independent? This is where I start to struggle tbh!

6 minutes ago, Tony Brooks said:

I think brushes would be a fair suspect then.

 

See Brian's post.

7 minutes ago, Tony Brooks said:

I think brushes would be a fair suspect then.

 

See Brian's post.

I'm gonna whip the pair of them out before it gets dark. Might do the alternators too. Ho-ho. Sigh.... Listen, thanks for your help! Take care!

 

[WotEver]

1 hour ago, Mark579 said:

Yes but the relay has not connected

This bit confuses me. According to what you’ve posted, if I’ve understood you correctly, both starter and domestic batts are showing identical voltages. Yes?  If so then they’re definitely connected together  by some method. 

 

Ditchcrawler’s post is well worth considering. 

[Mark579]

Hi Wotever, definitely have taken both Ditchcrawler and Tony's posts onboard. Both suggest alternator probs so currently both alternators are in the boot of the car ready to be looked at tomorrow. It's tricky trying to express issues on a forum in a text cos of all the ins and outs. I know a bit, but not enough, and I took Tony and Ditchcrawler as a consensus on the alts! Since Sunday I've replaced an exciter, a relay and measured all sorts, and was still stumped. The info on here is invaluable and I properly appreciate everyone's response, so I apologise if my posts haven't seemed grateful. I definitely am grateful though! Just been curled up in an unnatural position for a while removing alternators..??

[MtB]

 

Are you using the Smartgauge to measure the voltage(s)? 

 

If so all bets are off, unless you checked the accuracy of the calibration. They sold an unknown number of inaccurate instruments. 

[Tony Brooks]

7 hours ago, Mark579 said:

Hi Wotever, definitely have taken both Ditchcrawler and Tony's posts onboard. Both suggest alternator probs so currently both alternators are in the boot of the car ready to be looked at tomorrow. It's tricky trying to express issues on a forum in a text cos of all the ins and outs. I know a bit, but not enough, and I took Tony and Ditchcrawler as a consensus on the alts! Since Sunday I've replaced an exciter, a relay and measured all sorts, and was still stumped. The info on here is invaluable and I properly appreciate everyone's response, so I apologise if my posts haven't seemed grateful. I definitely am grateful though! Just been curled up in an unnatural position for a while removing alternators..??

I think you might have missed the point Brian made and I advised that you take heed of.

 

This could well be the alternators but two failing at the same time is  not common.

 

You state that you have a "Merlin battery management system" with no  model or part number so we can not look it up. The term battery management system means different things to different vendors so could be anything from an Amp hour counting meter, through a something controlling one alternator to something that combines both alternator outputs, messes about with it, and the passes charge to the batteries. In the later case then that unit or its wiring would be the more likely culprit because then one unit could easily mess up two alternator outputs.

 

I am also far from clear what this relay is that you mention unless you also have a Smartguage and Smartbank, a split charge relay being used to parallel both alternators, or rare alternators like the old Lucas AC series but in that case you would have two relays.

 

There is much on our side of the internet that we do not know so can not give very high quality advice, only general ideas based on common practice.

[Detling]

12 hours ago, Mike the Boilerman said:

 

Are you using the Smartgauge to measure the voltage(s)? 

 

If so all bets are off, unless you checked the accuracy of the calibration. They sold an unknown number of inaccurate instruments. 

yes but not out by almost 2 volts.

[WotEver]

11 minutes ago, Detling said:

yes but not out by almost 2 volts.

And not intermittent (14.05 down to 12.5), so a complete red herring. MtB’s simply using the thread as an excuse to have another bash at the product which is of no help whatsoever to the OP. 

6 hours ago, Tony Brooks said:

You state that you have a "Merlin battery management system" with no  model or part number so we can not look it up. The term battery management system means different things to different vendors so could be anything from an Amp hour counting meter, through a something controlling one alternator to something that combines both alternator outputs, messes about with it, and the passes charge to the batteries. In the later case then that unit or its wiring would be the more likely culprit because then one unit could easily mess up two alternator outputs.

Can you fill in the blanks, @Mark579?