Alternator temperature

[Keeping Up]

Alternators get quite hot when running, which almost certainly shortens their life. As I tend to fry my alternator quite often, I have been wondering about the factors that may affect this.

 

My alternator is controlled by an Adverc (external controller) which increases the output voltage to overcome the voltage drop in my ancient wiring and blocking diodes. When running hard the alternator putting out 70 amps. If it were connected directly to the battery that would be at about 14.4 volts, but with my setup there is probably nearer to 16v at the B+ terminal.

 

So my question is, how much hotter does the alternator get by producing the same current at a higher voltage? The power dissipated in the resistance of the windings is the same, and the same goes for the power dissipated in the rectifier diodes. The internal circuitry on the D+ line consumes very little power anyway, so at first thoughts the alternator will not get any hotter despite having to produce more power - but is this really the case or not?

 

 

 

 

[Albion]

Alternators get quite hot when running, which almost certainly shortens their life. As I tend to fry my alternator quite often, I have been wondering about the factors that may affect this.

 

My alternator is controlled by an Adverc (external controller) which increases the output voltage to overcome the voltage drop in my ancient wiring and blocking diodes. When running hard the alternator putting out 70 amps. If it were connected directly to the battery that would be at about 14.4 volts, but with my setup there is probably nearer to 16v at the B+ terminal.

 

So my question is, how much hotter does the alternator get by producing the same current at a higher voltage? The power dissipated in the resistance of the windings is the same, and the same goes for the power dissipated in the rectifier diodes. The internal circuitry on the D+ line consumes very little power anyway, so at first thoughts the alternator will not get any hotter despite having to produce more power - but is this really the case or not?

My feeling is that many alternators on nbs get fried because of lack of ventilation. If you think about it the alternators on cars are in a fairly well ventilated and draughty environment whereas on a boat they are in still air, often cocooned in a boxed in engine compartment with (sometimes) sound deadening material to add to the heat transfer problems AND expected to output higher continuous currents than a car alternator is likely to be asked to provide. Ensure that there is adequate ventilation slots near the alternator so that the alternator's fan has a chance to cool it and a lot of problems would be solved IMO.

Roger

[Ex- Member]

Alternators get quite hot when running, which almost certainly shortens their life. As I tend to fry my alternator quite often, I have been wondering about the factors that may affect this.

 

My alternator is controlled by an Adverc (external controller) which increases the output voltage to overcome the voltage drop in my ancient wiring and blocking diodes. When running hard the alternator putting out 70 amps. If it were connected directly to the battery that would be at about 14.4 volts, but with my setup there is probably nearer to 16v at the B+ terminal.

 

So my question is, how much hotter does the alternator get by producing the same current at a higher voltage? The power dissipated in the resistance of the windings is the same, and the same goes for the power dissipated in the rectifier diodes. The internal circuitry on the D+ line consumes very little power anyway, so at first thoughts the alternator will not get any hotter despite having to produce more power - but is this really the case or not?

 

 

 

 

 

Probably a question that can't be answered generally as there are too many variables, for example your exact set up.

 

Most boat engines will not spin alternators very fast in the first place. I had to increase my pulley size by 2.5 so to be able to run the alternator at between 5 and 6000 Rpm when running in idle which is generally where most general alternattors put out their rated amps.

 

So your adverc might get more efficiency but your altternator might only be running at 3000 rpm where my alternator will be running a 55000 RPM with a sterling charge controller set up. At the end of the dat the more output requires more effort which in turn probably creates more friction so will be hotter.

 

An alternator on a boat shouldn't get too hot, they spin much faster in cars and vans and have high output especially at night with lights heater fans etc running.

 

My feeling is that many alternators on nbs get fried because of lack of ventilation. If you think about it the alternators on cars are in a fairly well ventilated and draughty environment whereas on a boat they are in still air, often cocooned in a boxed in engine compartment with (sometimes) sound deadening material to add to the heat transfer problems AND expected to output higher continuous currents than a car alternator is likely to be asked to provide. Ensure that there is adequate ventilation slots near the alternator so that the alternator's fan has a chance to cool it and a lot of problems would be solved IMO.

Roger

 

 

alternators on nbs get fried because of lack of ventilation

 

 

 

I'm unsure about that. our engine is in a well ventilated engine room surrounded by cold steel, all alternators have similar fans so self cool. I would bet that ythe ambient temperature inside a car or van engine comparment is a lot hotter than that of any boat engine.

Edited February 16, 2013 by Julynian

[dmr]

The heat generated in the windings (copper loss) is only related to current (current squared in fact). Diode heat loss is proportional to current (more or less). There is also an "iron loss" in the core of the alternator that is also current related.

 

By raising the charge voltage with the Adverc the current into the batteries is increased so the alternator will work harder.

but but but

It is only during the bulk phase that the alternator is working flat out and the Adverc can not raise the voltage when the alternator is flat out!

During the acceptance phase the voltage IS increased but the current is low so the alternator is not working hard.

There is a brief period at the bulk-acceptance transition when the Adverc will increase the voltage at near full current.

The makers of alternator controllers infer that they make the alternator work much harder but I reckon this is marketing BS.

 

Don't make the alternator work too hard at very low speeds when its fan is less effective, and keep the alternator free of dust...dog hairs are the killer.

 

..........Dave

[Albion]

I'm unsure about that. our engine is in a well ventilated engine room surrounded by cold steel, all alternators have similar fans so self cool. I would bet that ythe ambient temperature inside a car or van engine comparment is a lot hotter than that of any boat engine.

A car engine supplied with air from a 60 mph air supply has less air flow than an engine room with no air flow? Hhhm, don't think so.

Roger

[Alan de Enfield]

I know nothing !!! (but I can cut & paste)

 

http://www.electronics-cooling.com/2002/05/thermal-design-challenges-in-automotive-alternator-power-electronics/

 

Admittedly, the thermal designs of these early alternators weren’t particularly taxing. Since that time, though, there has been an ever-increasing demand for on-board electrical power from the alternator. When alternators first appeared in the 1960′s, power requirements were typically 500 W. In the 1980′s this power demand escalated to 1500 W. Today, many production alternators are capable of 2000 W and designs are being developed that provide upwards of 3000 W of electrical output power. Accompanying this increase in electrical performance has been a proportional increase in heat loss of the rectifier bridge since its thermal losses are essentially linear with output power.

 

The thermal challenges have also been compounded by the rise in underhood ambient temperatures in automotive vehicles. In the 1960′s the typical underhood inlet cooling air temperature to the alternator was 90oC. By the 1980′s this had jumped up to 110oC. Today, applications approach the 130oC range.

 

I'd be a little worried if my engine-ole was at these sort of temperatures

[Ex- Member]

A car engine supplied with air from a 60 mph air supply has less air flow than an engine room with no air flow? Hhhm, don't think so.

Roger

 

I didn't mention air flow, I said ambient temperature. Also a car doesn't always do sixty miles per hour, there's things called traffic jams. Vehicle engine compartments are pretty sealed with soundproofing and in a confined space where as boat engines are in a bigger space surrounded by cold steel and with ventilation unless incorrectly fitted. Most engines at idle will run at similar temperatures an engine in a smaller confined space will likely create a higher ambient temperature.

[Albion]

I didn't mention air flow, I said ambient temperature. Also a car doesn't always do sixty miles per hour, there's things called traffic jams. Vehicle engine compartments are pretty sealed with soundproofing and in a confined space where as boat engines are in a bigger space surrounded by cold steel and with ventilation unless incorrectly fitted. Most engines at idle will run at similar temperatures an engine in a smaller confined space will likely create a higher ambient temperature.

And when in a traffic jam a large electric fan cuts in to increase air flow and reduce ambient temperature. Sorry, your comparison just doesn't compare. How many boat engines have electric thermo-controlled fans even in a stifling closed engine space?

Roger

[Ex- Member]

And when in a traffic jam a large electric fan cuts in to increase air flow and reduce ambient temperature. Sorry, your comparison just doesn't compare. How many boat engines have electric thermo-controlled fans even in a stifling closed engine space?

Roger

 

None they don't need any, exacttly my point, thank you

 

 

The cooling of a correcly fitted boat engine will be more efficient than a car or van engine. The boat engine is constantly connected to a cooling device, so it doesn't get hot and require furtther assistance from a fan. When a car is idling the engine temp will rise as there's no air flow through i's radiator to cool it and the engine. This engine is in a confined space which will greate a high ambient temperature as the engine temp rises. when this engine effecttively begins to overheat a thermostat will kick in to operate he fan to cool the radiator and begin cooling the engine, until that happens the engine will run hotter than a boat enging being consantly cooled by canal water.

 

A boat engine doesnt require a fan it is cooled from canal water which is consantly cooling. So when idling a comparable engine in a boat will be being cooled at a constant from a source and not overheat (IE canal water) which in any case is substantially cooler than air in temperatures above freezing point and more so in tthe summer.

Edited February 16, 2013 by Julynian

[OldGoat]

I think the answer is simpler that all of the above.

Most boats use normal automotive alternators. Their duty cycle is I suspect about 25%. That is they are designed to top up the battery as a result of the car standing still and consuming some energy and starting the car. Thereafter they supply energy to all the electrical equpment plus an allowance for every car having all the addon goodies that could be fitted (extra lights, what passes for in car entertainment etc).

 

Thes unfortunate devices are fitted to boats, where they run at constant speed at near maximum output for hours on end.

Of course they get hot.

 

I've fitted large bus / commercial vehicle alternators to my boat - these are designed to work hard all day, even so they get hot - but not that hot..

You pays your money....

[by'eck]

Alternators get quite hot when running, which almost certainly shortens their life. As I tend to fry my alternator quite often, I have been wondering about the factors that may affect this.

 

My alternator is controlled by an Adverc (external controller) which increases the output voltage to overcome the voltage drop in my ancient wiring and blocking diodes. When running hard the alternator putting out 70 amps. If it were connected directly to the battery that would be at about 14.4 volts, but with my setup there is probably nearer to 16v at the B+ terminal.

 

So my question is, how much hotter does the alternator get by producing the same current at a higher voltage? The power dissipated in the resistance of the windings is the same, and the same goes for the power dissipated in the rectifier diodes. The internal circuitry on the D+ line consumes very little power anyway, so at first thoughts the alternator will not get any hotter despite having to produce more power - but is this really the case or not?

 

The greatest electrical loss in an alternator is I²R (=power) ohmic loss in the stator windings. There is a similar loss in the rotor but much less.

 

Then there's the two magnetic losses in the stator core. Eddy currents, reduced by having a laminated core with oxide insulation between, and hysteresis loss caused by the AC magnetic flux.

 

They all add to the heat produced and wasted.

[nb Innisfree]

When our 24v 100 amp alternator is cold and in bulk charge, according to the ammeter it puts 100 amps into the batts at approx 2800 rpm rotor speed, but when it's putting just a few amps into the batteries a few hour later and we switch the w/m on it requires approx 3600 rpm to achieve the same.

[Keeping Up]

The greatest electrical loss in an alternator is I²R (=power) ohmic loss in the stator windings. There is a similar loss in the rotor but much less.

 

Then there's the two magnetic losses in the stator core. Eddy currents, reduced by having a laminated core with oxide insulation between, and hysteresis loss caused by the AC magnetic flux.

 

They all add to the heat produced and wasted.

 

Yes, but which of them (if any) increase if the voltage has to be increased but the current is unchanged?

 

The I²R los in the stator winding isn't going to increase if the voltage is increased, at the same current. Similarly I don't think the loss in the rotor windings will increase because I assume the current in them will also be unchanged (or will it?).

 

I don't know about the magnetic losses in the stator core, I wonder if they'd increase (and if so, are they significant)

 

I wouldn't expect the eddy current losses to be significant in a well-designed alternator - but again I don't know and I'm happy to be corrected.

 

And I don't know about the hysteresis losses either.

 

I still just don't have a feeling for how much, if at all, the alternator will get hotter by producing 10% more voltage at the same power (or conversely, how much cooler the alternator would be if the split charge diodes were replaced by a relay)

[ditchcrawler]

Yes, but which of them (if any) increase if the voltage has to be increased but the current is unchanged?

 

The I²R los in the stator winding isn't going to increase if the voltage is increased, at the same current. Similarly I don't think the loss in the rotor windings will increase because I assume the current in them will also be unchanged (or will it?).

 

I don't know about the magnetic losses in the stator core, I wonder if they'd increase (and if so, are they significant)

 

I wouldn't expect the eddy current losses to be significant in a well-designed alternator - but again I don't know and I'm happy to be corrected.

 

And I don't know about the hysteresis losses either.

 

I still just don't have a feeling for how much, if at all, the alternator will get hotter by producing 10% more voltage at the same power (or conversely, how much cooler the alternator would be if the split charge diodes were replaced by a relay)

You will also have I²R losses in the cables to the batteries.

[Keeping Up]

You will also have I²R losses in the cables to the batteries.

 

 

Yes - but again they won't change, at the same level of current, unless the cables are changed.

 

The biggest waste of power is the split-charge diodes, dissipating about 65 watts and probably increasing the ambient temperature in the engine bay very slightly. But if it does this without making the alternator run significantly warmer, it is not an issue.

[ditchcrawler]

Yes - but again they won't change, at the same level of current, unless the cables are changed.

 

The biggest waste of power is the split-charge diodes, dissipating about 65 watts and probably increasing the ambient temperature in the engine bay very slightly. But if it does this without making the alternator run significantly warmer, it is not an issue.

But you started off asking about the difference now you have the Advec to make up the volt drop. Now the voltage has increased to compensate for cable etc loss the total current flow will have increased. V*I also gives you power.

[Albion]

None they don't need any, exacttly my point, thank you

 

 

The cooling of a correcly fitted boat engine will be more efficient than a car or van engine. The boat engine is constantly connected to a cooling device, so it doesn't get hot and require furtther assistance from a fan. When a car is idling the engine temp will rise as there's no air flow through i's radiator to cool it and the engine. This engine is in a confined space which will greate a high ambient temperature as the engine temp rises. when this engine effecttively begins to overheat a thermostat will kick in to operate he fan to cool the radiator and begin cooling the engine, until that happens the engine will run hotter than a boat enging being consantly cooled by canal water.

 

A boat engine doesnt require a fan it is cooled from canal water which is consantly cooling. So when idling a comparable engine in a boat will be being cooled at a constant from a source and not overheat (IE canal water) which in any case is substantially cooler than air in temperatures above freezing point and more so in tthe summer.

 

But the alternator (which is what we are talking about) doesn't benefit from that cooling source so we can ignore that, even if your argument is correct. The alternator is sitting in a still air environment, heated by its own efficiency losses (power in equals power out plus friction, plus windage, plus noise, plus power losses in the windings etc) and the raised temperature of the engine bay (caused by the hot engine). Unless it is cooled adequately while it is being required to replace the many hundreds of amp-hours that you have taken from your batteries the previous night it will work hotter than in a vehicle engine bay. The more boxed in the engine, the greater the ambient temperature, and the worse the environment for the alternator. As there is no natural air flow in that area then the alternator doesn't operate in ideal conditions given the work that it is required to do compared to its normal vehicle engine bay environment. Even some car manufacturers have had to add a more efficient cooling source for their alternators (Jags provided a cool air duct to the rear of the alternator, BMW used some water cooled alternators IIRC, so if they felt it was necessary in an engine bay with some air flow then nb alternators are not operating ideally given that they have to deliver many more amps for longer periods than a car and are often being driven harder by an external regulator/charge controller.

Roger

[Keeping Up]

But you started off asking about the difference now you have the Advec to make up the volt drop. Now the voltage has increased to compensate for cable etc loss the total current flow will have increased. V*I also gives you power.

 

 

No, maybe I didn't make it clear. I've always had the Adverc (well since 1997 anyway, before that it was a Kestrel); I've just been wondering whether the alternator would run cooler if I were to change the existing diodes to either a relay or zero-volt diodes - in the hope of making the alternators last for longer. The change wouldn't affect the current at all, it would merely reduce the output voltage from the alternator.

 

If it would make little or no difference to the life of the alternator then the considerable expense (enough to buy two new alternators) just isn't worth it.

[Ex- Member]

But the alternator (which is what we are talking about) doesn't benefit from that cooling source so we can ignore that, even if your argument is correct. The alternator is sitting in a still air environment, heated by its own efficiency losses (power in equals power out plus friction, plus windage, plus noise, plus power losses in the windings etc) and the raised temperature of the engine bay (caused by the hot engine). Unless it is cooled adequately while it is being required to replace the many hundreds of amp-hours that you have taken from your batteries the previous night it will work hotter than in a vehicle engine bay. The more boxed in the engine, the greater the ambient temperature, and the worse the environment for the alternator. As there is no natural air flow in that area then the alternator doesn't operate in ideal conditions given the work that it is required to do compared to its normal vehicle engine bay environment. Even some car manufacturers have had to add a more efficient cooling source for their alternators (Jags provided a cool air duct to the rear of the alternator, BMW used some water cooled alternators IIRC, so if they felt it was necessary in an engine bay with some air flow then nb alternators are not operating ideally given that they have to deliver many more amps for longer periods than a car and are often being driven harder by an external regulator/charge controller.

Roger

 

 

 

 

The more boxed in the engine, the greater the ambient

temperature, and the worse the environment for the alternator.Exactly as i stated, thank you again.

 

But the alternator (which is what we are talking about) doesn't benefit from that cooling source.

 

Blimy what are you on. If he alternator is connected to the engine, the cooling fan on that alternator is using that agent to help cool it's self, if the ambient air temperature is lower then the air it uses to cooler is as well.

 

Hardly to be ignored surely

 

But the alternator (which is what we are talking about)

 

As you know well I was replying you your comment about engine room ventilation.

 

You replied to the following.

 

I'm unsure about that. our engine is in a well ventilated engine room surrounded by cold steel, all alternators have similar fans so self cool. I would bet that the ambient temperature inside a car or van engine comparment is a lot hotter than that of any boat engine.

 

Which you have now confirmed, so thank you once again.

Edited February 16, 2013 by Julynian

[by'eck]

Yes, but which of them (if any) increase if the voltage has to be increased but the current is unchanged?

 

The I²R los in the stator winding isn't going to increase if the voltage is increased, at the same current. Similarly I don't think the loss in the rotor windings will increase because I assume the current in them will also be unchanged (or will it?).

 

I don't know about the magnetic losses in the stator core, I wonder if they'd increase (and if so, are they significant)

 

I wouldn't expect the eddy current losses to be significant in a well-designed alternator - but again I don't know and I'm happy to be corrected.

 

And I don't know about the hysteresis losses either.

 

I still just don't have a feeling for how much, if at all, the alternator will get hotter by producing 10% more voltage at the same power (or conversely, how much cooler the alternator would be if the split charge diodes were replaced by a relay)

 

Whilst current is clearly the major player in alternator losses, an increase in its output voltage gives an increase in efficiency. Any means by way of changing load to increase output voltage will therefore be beneficial but to a small degree.

 

As mentioned elsewhere a TravelPower or Dynawatt with its alternator running at around 250 volts makes for a more compact design for it potential power output.

[Keeping Up]

Whilst current is clearly the major player in alternator losses, an increase in its output voltage gives an increase in efficiency. Any means by way of changing load to increase output voltage will therefore be beneficial but to a small degree.

 

As mentioned elsewhere a TravelPower or Dynawatt with its alternator running at around 250 volts makes for a more compact design for it potential power output.

 

Hmmm, I'm still not sure. I agree with what you say that it is more efficient to operate at a higher voltage. But in this scenario, where the voltage is increased but the current remains the same,my gut feeling is that the increased power output might match the efficiency increase preicsely so that the power (and hence the heat) dissipated inside the alternator is unchanged. But I'm still not convinced either way.

[by'eck]

Hmmm, I'm still not sure. I agree with what you say that it is more efficient to operate at a higher voltage. But in this scenario, where the voltage is increased but the current remains the same,my gut feeling is that the increased power output might match the efficiency increase preicsely so that the power (and hence the heat) dissipated inside the alternator is unchanged. But I'm still not convinced either way.

 

Well a practical example. My alternator is running at or near near max current and on the (Sterling DAR) regulator voltage limit of 14.6 volts as it charges batteries. When I put a large electrical load (kettle) on the inverter, the battery/alternator output voltage (not surprisingly) drops and the engine load increases very noticeably - this is apparent since I have a very vocal engine

 

So to come back to your OP - leave as is. Lowering the regulated alternator output voltage will create more heat. If you regularly fry your alternator, look to ways of keeping it running cooler - increased revs/fan speed maybe.

[Arthur Brown]

Heat is a function of current squared, cooling is a function of fan speed. If the fan/alternator speed is too low then the alternator may well fry.

 

If fried alternators is a feature then please check the fan is turning the right way and fast enough.

[smileypete]

Hmmm, I'm still not sure. I agree with what you say that it is more efficient to operate at a higher voltage. But in this scenario, where the voltage is increased but the current remains the same,my gut feeling is that the increased power output might match the efficiency increase preicsely so that the power (and hence the heat) dissipated inside the alternator is unchanged. But I'm still not convinced either way.

Would have though higher power means more iron losses, which means more heat and so more copper losses. Also the stator needs more current, so more heat there too.

 

The internal regulator is likely to have a built in temperature coefficient which will help protect the alt a little but be bypassed by using an external regulator.

 

Do you know which bit blows up - stator, rotor, regulator, rectifier? Maybe put a thermal switch on the alt body to switch off the external reg or even the field off when it gets too hot.

 

cheers, Pete.

~smpt~

[by'eck]

Heat is a function of current squared, cooling is a function of fan speed. If the fan/alternator speed is too low then the alternator may well fry.

 

If fried alternators is a feature then please check the fan is turning the right way and fast enough.

 

Exactly, so voltage has only a minor secondary effect on alternator loss as indicated by this graph.