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Dr Bob

Alternator temperature

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Need some clever person who knows about alternators.

I need to understand the temperature limits of alternators.

I have recently installed lithium batteries and hence my domestic alternator is having to do some work. Alternator is a bog standard 90A fitted to a Beta 43 - looks like the original unit. Typically on the lead acid batteries (6*110Ahr) it produces 60A on start up of the engine (when around 70-80% Soc) dropping to 30A after an hour and then 15A after another etc. No problems operating it. Never measured temperature on it.

With the Lithiums I see a constant Amps out depending on how I set it. Yesterday it was generating a solid 45A for 2 hours. I measured the temperature in the centre of the casing at 80°C (see pic below). Measurement point was at the join of the two halves of the casing ie in the middle of the top of the alternator. Today the charge current started at 55A and held at that for 2 hours and the temp was up to 92°C (it did reduce to 70°C when the current dropped to 35A when doing 3 locks at tickover). Is this temperature too high?

Now, the reason I ask is that the temp at the back of the alternator (ie at the left of the picture) was a max of 60°C and at the lower charge rate was 45-50°C. The temp sensing lead to turn off the charge current is bolted at the back, just under the red cable and that was at this lower temp range. The temp sensing lead cuts off the charge at 90°C. I guess all the electronic gubbins including diodes is at the back of the alternator so seeing much lower temps than the casing near the front.

Most of the literature says keep the alternator below 90°C but where are they measuring this temperature?

What do you think the safe operating temperature levels are?

The general high temps around the engine - ie the coolant tanks are 70-80°C.

IMG_20190321_141720.jpg

Edited by Dr Bob

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Just now, rusty69 said:

You need @Sir Nibble

Well I know but he hasnt been around for a while.

Thanks for the '@' thingy. I'd forgotten to do that. Maybe Tumshie will know as well?

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50 minutes ago, Dr Bob said:

Need some clever person who knows about alternators.

I need to understand the temperature limits of alternators.

I have recently installed lithium batteries and hence my domestic alternator is having to do some work. Alternator is a bog standard 90A fitted to a Beta 43 - looks like the original unit. Typically on the lead acid batteries (6*110Ahr) it produces 60A on start up of the engine (when around 70-80% Soc) dropping to 30A after an hour and then 15A after another etc. No problems operating it. Never measured temperature on it.

With the Lithiums I see a constant Amps out depending on how I set it. Yesterday it was generating a solid 45A for 2 hours. I measured the temperature in the centre of the casing at 80°C (see pic below). Measurement point was at the join of the two halves of the casing ie in the middle of the top of the alternator. Today the charge current started at 55A and held at that for 2 hours and the temp was up to 92°C (it did reduce to 70°C when the current dropped to 35A when doing 3 locks at tickover). Is this temperature too high?

Now, the reason I ask is that the temp at the back of the alternator (ie at the left of the picture) was a max of 60°C and at the lower charge rate was 45-50°C. The temp sensing lead to turn off the charge current is bolted at the back, just under the red cable and that was at this lower temp range. The temp sensing lead cuts off the charge at 90°C. I guess all the electronic gubbins including diodes is at the back of the alternator so seeing much lower temps than the casing near the front.

Most of the literature says keep the alternator below 90°C but where are they measuring this temperature?

What do you think the safe operating temperature levels are?

The general high temps around the engine - ie the coolant tanks are 70-80°C.

IMG_20190321_141720.jpg

They suck their cooling air in at the back. It'll probably get even hotter in the summer when the engines running with the lid on especially if its a metal cover with the sun beating on it. .  I'd get a set of ordinary LA batteries. 

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I am neither clever nor knowledgeable about alternators. My first port of call would be Snibble (as suggested) and if he is no longer around, I would email a couple of alternator manufacturers or similar for their advice. 
I have known people to air cool alternators within boats using a fan and ducting, since they don't get as much air as a road vehicle etc, Never measured our alt. temp. but it gets good and hot even with LA batteries.

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The two parts that create heat are the diode pack that is usually right at the back where cool air is drawn in and the stater that is the laminated middle section. (I think your stator is inside the two end pieces).

 

I have no definitive temperature data or limits but know that you can give yourself a burn on an alternator that has been working hard for a while. I doubt there is an issue with the diode temperature and when you realise some cars stuck the alternator between a transverse engine and bulkhead close to the exhaust manifold I think it  will run with the centre section much hotter than 90C, the main thing you would be worrying about is the insulating lacquer on the stator winding burning away and causing a short.  I have seen alternators that smoked when reverse polarity connected work perfecter well when reconnected the correct way round but the idiot was PDQ at disconnecting it - assisted by a great big spark!

 

Not sure that helps much and hope Sir N will be along soon.

 

Edited to add - none of my auto-electrical text books, including Payne's Marine Electrical and Electrocution Bible seem to give any maximum temperatures. You also need to keep the solder joints on the diodes    at below melting point but I expect that will be getting on for 200C

Edited by Tony Brooks
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6 minutes ago, Tony Brooks said:

The two parts that create heat are the diode pack that is usually right at the back where cool air is drawn in and the stater that is the laminated middle section. (I think your stator is inside the two end pieces).

 

I have no definitive temperature data or limits but know that you can give yourself a burn on an alternator that has been working hard for a while. I doubt there is an issue with the diode temperature and when you realise some cars stuck the alternator between a transverse engine and bulkhead close to the exhaust manifold I think it  will run with the centre section much hotter than 90C, the main thing you would be worrying about is the insulating lacquer on the stator winding burning away and causing a short.  I have seen alternators that smoked when reverse polarity connected work perfecter well when reconnected the correct way round but the idiot was PDQ at disconnecting it - assisted by a great big spark!

 

Not sure that helps much and hope Sir N will be along soon.

Thanks Tony, catweasle and Bizz.

Ok good to know the diodes are at the back and that's where the cooling is coming in. Yes it will be hotter in the summer - I hope! I will keep an eye on temps and restrict to charging at no more than 55A for now.

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Hasn't your son got one of dem BMW's with a water cooled alternator? You could borrow it when he aint looking doc!

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Just now, rusty69 said:

Hasn't your son got one of dem BMW's with a water cooled alternator? You could borrow it when he aint looking doc!

But he may notice if you take the engine ECU as well so you can control it. Not sure a Pi would be up to the job.

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23 minutes ago, rusty69 said:

Hasn't your son got one of dem BMW's with a water cooled alternator? You could borrow it when he aint looking doc!

.....bloody BMW?

It would probably break down again and need a new BMS.

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1 hour ago, Tony Brooks said:

Not sure a Pi would be up to the job.

A Pi would do the job with time to spare. The ECU is doing alternator control as a spare time job too, along with sorting out the individual fuel injections several times per revolution and monitoring the exhaust and a few other jobs.

 

The hard part would be getting the data to the Pi and working out what to do with it in a canal type application.

 

N

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1 minute ago, BEngo said:

A Pi would do the job with time to spare. The ECU is doing alternator control as a spare time job too, along with sorting out the individual fuel injections several times per revolution and monitoring the exhaust and a few other jobs.

 

The hard part would be getting the data to the Pi and working out what to do with it in a canal type application.

 

N

Nah. Just stick the beemer on the roof of the boat and relocate alternator. Sorted!.....until you get to a bridge.

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1 hour ago, Tony Brooks said:

You also need to keep the solder joints on the diodes    at below melting point but I expect that will be getting on for 200C

The solder joints on one of our alternators used to melt until i realised the battery was seriously knackered. 

Edited by rusty69

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13 minutes ago, rusty69 said:

The solder joints on one of our alternators used to melt until i realised the battery was seriously knackered. 

 

I suspect that was caused by the very high current in the thin diode connection rather than "normal" currents. Alternators are actually rated in Watts so the so many amps designation we use is not really true. Lets say an alternator is rated at 60 amps. That means at 12V it will deliver 720 Watts. Now with knackered and probably shorting batteries the charging voltage could be 6 volts and that will allow 120 amps to flow hence overheating of conductors designed for a nominal 60 amps. I din't think this will be any sort of an issue for the good doctor's setup as long as he ensures the current is limited to the alternator's nominal rating.

 

 

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It was a while ago now but I think an alternator manufacture told me that the maximum intermittent winding temperature was 120 degrees. In many thing engineering the life expectancy is closely and inversely related to temperature, My 100 amp alternators have run very hot when worked hard, a big bank of well discharged Trojans is much the same as a lithium bank as far as the alternator is concerned. So far the slips rings have given out before the windings or diodes have melted (touching wood is easy in a narrowboat).

 

................Dave

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 Do you know who manufactured the alternator, the OEM may have details.

 

The alternators on our boat are Leece Neville (Prestolite) For the specificities alternators that are fitted the specification of output is given for two conditions 25C and 93C (Ouch!).  In addition the general specifications of their alternators provided this information:

 

2.10. The regulation voltage is affected by the temperature coefficient of the regulator. This is normally a negative parameter in the range -5mV/K to -15mV/K and has the effect of reducing the battery charging voltage as the regulator temperature increases. This assists in matching the alternator voltage to the battery temperature characteristic. The exact value is regulator dependent and may be obtained from Prestolite. The selected parameter must be correctly matched to the battery type and operating conditions to avoid under or overcharge conditions.

 

If yours is similar you will see a significant voltage reduction at the temperatures you have measured (0.9V for a 60C rise in temperature) and this may explain your current changes.

 

Leece Neville also give curves showing the current output and for the specificities alternator we have the current is a max of 90A at 25C and 83 at 93C, so there is another effect at play as well.

8MR2070TA_curve.jpg.6ea10487750fe2d28ad6413a93b62137.jpg

I Note Tony Brook's comment on current being much higher if the delivery voltage is low, this may not be universally applicable, the Leece Neville alternators are auto current limiting so will not double in current for a 6V battery voltage.

 

 

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25 minutes ago, Tony Brooks said:

 I din't think this will be any sort of an issue for the good doctor's setup as long as he ensures the current is limited to the alternator's nominal rating.

 

 

Thanks Tony, yes I will ensure I keep the amps down. I think 55A amps is probably the most I will try initially and likely 45A if doing long days.

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What affect (effect) does the use of an alternator to battery charger have on the alternator temperature? I recall you have one. 

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10 minutes ago, dmr said:

It was a while ago now but I think an alternator manufacture told me that the maximum intermittent winding temperature was 120 degrees. In many thing engineering the life expectancy is closely and inversely related to temperature, My 100 amp alternators have run very hot when worked hard, a big bank of well discharged Trojans is much the same as a lithium bank as far as the alternator is concerned. So far the slips rings have given out before the windings or diodes have melted (touching wood is easy in a narrowboat).

 

................Dave

Thanks Dave, That's a bit more confidence that I am ok at the current temperatures.

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14 minutes ago, dmr said:

In many thing engineering the life expectancy is closely and inversely related to temperature,

As a rule of thumb for most things electrical and electronic, a 10C rise in continuous operating  temperature halves the life. 20C rise, drops life to a quarter and so on. This is provided a new failure mechanism, like the solder joints melting, or the winding insulation catching fire doesn't intervene first and finish it off.

 

Jen

Edited by Jen-in-Wellies

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7 minutes ago, jonesthenuke said:

 Do you know who manufactured the alternator, the OEM may have details.

 

The alternators on our boat are Leece Neville (Prestolite) For the specificities alternators that are fitted the specification of output is given for two conditions 25C and 93C (Ouch!).  In addition the general specifications of their alternators provided this information:

 

2.10. The regulation voltage is affected by the temperature coefficient of the regulator. This is normally a negative parameter in the range -5mV/K to -15mV/K and has the effect of reducing the battery charging voltage as the regulator temperature increases. This assists in matching the alternator voltage to the battery temperature characteristic. The exact value is regulator dependent and may be obtained from Prestolite. The selected parameter must be correctly matched to the battery type and operating conditions to avoid under or overcharge conditions.

 

If yours is similar you will see a significant voltage reduction at the temperatures you have measured (0.9V for a 60C rise in temperature) and this may explain your current changes.

 

Leece Neville also give curves showing the current output and for the specificities alternator we have the current is a max of 90A at 25C and 83 at 93C, so there is another effect at play as well.

8MR2070TA_curve.jpg.6ea10487750fe2d28ad6413a93b62137.jpg

I Note Tony Brook's comment on current being much higher if the delivery voltage is low, this may not be universally applicable, the Leece Neville alternators are auto current limiting so will not double in current for a 6V battery voltage.

 

 

Thanks JTN.

I had seen that data before. The question though is where are they measuring the temperature? The temp on mine varies from 50 to 90 across the top (from back to front). It is good to see that they are quoting data at 93C as that means they must be anticipating it operating at that temp....but then again ....which part of the alternator is at 93°C.

3 minutes ago, Jen-in-Wellies said:

As a rule of thumb for most things electrical and electronic, a 10C rise in continuous operating  temperature halves the life. 20C rise, drops life to a quarter and so on. This is provided a new failure mechanism, like the solder joints melting, or the winding insulation catching fire doesn't intervene first and finish it off.

 

Jen

Same for chemical reactions. 10°C doubles the reaction rate.

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Just now, Dr Bob said:

Thanks JTN.

I had seen that data before. The question though is where are they measuring the temperature? The temp on mine varies from 50 to 90 across the top (from back to front). It is good to see that they are quoting data at 93C as that means they must be anticipating it operating at that temp....but then again ....which part of the alternator is at 93°C.

Good question and I have been searching their (generally helpful) site for such info and have not found any. As they are discussing the temperature regulation I would think it may be the temperature of the regulator but cannot be sure.

 

Can you reduce the operating temperature in any way? I have fitted some computer fans to cool the alternators on our boat. IIRC they run a lot cooler than yours, I wanted them to run cooler just to improve longevity and it was easy to accomplish.

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3 minutes ago, Jen-in-Wellies said:

As a rule of thumb for most things electrical and electronic, a 10C rise in continuous operating  temperature halves the life. 20C rise, drops life to a quarter and so on. This is provided a new failure mechanism, like the solder joints melting, or the winding insulation catching fire doesn't intervene first and finish it off.

 

Jen

You sound like an electronic engineer 😀, there's a lot of us on this forum. Does that law apply primarily to semiconductors where temperature is a big and understood factor? I am not sure it would apply to winding varnish but do confess that I know nothing at all about this.

 

..............Dave

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