Hitachi Alterrnator performance curve.

[rigpigpaul]

Hi All, I have been looking at the performance of my 60 amp alternator and see that it has to run at 6000rpm to achieve 62 amps @13.5 volts. At 2500 rpm which is my cruising revs it only puts out 40 amps I want to fit a stirling allternator regulator to increase performance. Question-could I alter the size of the pulleys, engine or alternator , to run the alternator faster at lower engine revs to charge the batteries. Or am I missing something?
Thanks in anticipation RPP.

 

[Talulah]

The max output of 40 amps at 2500 revs won't be increased by adding a Sterling Alt Reg. It is a physical limitation of the alternator.
However, at 2500 revs the real output will depend upon the voltage of the battery. You can increase this real output (upto the max 40 amps) by fitting a Sterling Alt Reg. (In effect the Sterling Reg forces the alternator to work harder for the same battery voltage.)

Changing the pulleys will have an effect but you could exceed the max rpm of the alternator when the engine is running at max revs.

In summary, don't worry about the max output at different revs but increase charging performance by fitting a Sterling Alt reg or Adverc or similar.

 

[little_roundtop]

Umm, the speed of rotation of your alternator is not the same as the speed of rotation of your engine. Your alternator rotates much faster than your engine.

 

[halcyon]

Hi All, I have been looking at the performance of my 60 amp alternator and see that it has to run at 6000rpm to achieve 62 amps @13.5 volts. At 2500 rpm which is my cruising revs it only puts out 40 amps I want to fit a stirling allternator regulator to increase performance. Question-could I alter the size of the pulleys, engine or alternator , to run the alternator faster at lower engine revs to charge the batteries. Or am I missing something?
Thanks in anticipation RPP.

Some where between 2,500 and 6,000 rpm, probably nearer 2,500, the alternator output will stop increasing, and flat line. This output is limited by the stator coil size, altering things will not increase it, to increase output further you need more windings in the stator. That's why alternators get bigger as you increase output, if you could increase output another way the manufactures would have done it years ago.

So yes, you need to alter the pulleys to get you to the flat part of the output graph at cruising rpm, just a little simple maths.

Brian

 

[jaba]

Consider also the Sterling Alternator to Battery charger. I use it with an Hitachi alternator and I am very happy. Mind also that, as Talulah wrote, it's not the maximum output of the alternator that matters but it's will to provide such output to the batteries. This is where the Alt2Batt (or the smart regulator) comes into play.

j

 

[truscott]

Umm, the speed of rotation of your alternator is not the same as the speed of rotation of your engine. Your alternator rotates much faster than your engine.

So are power curve graphs a representation of the rpm at the Alternator Pulley?

If so, what elements do we have to know in order to work out the minimum Engine RPM we need to reach that optimum output?

I'm assuming that the size of the flywheel pulley, the belt circumference and the alternator pulley size are factors, but would appreciate any insight anyone can offer.

We will be spending a few days at anchor over the next month and a bit and I've not got around to putting any alternative charging sources onboard yet, so am depending on running the engine for a while to top up the batteries (I'm assured that for the amount of motoring we do, glazing isn't going to be an issue just yet).

Cheers, PT.

 

[AntarcticPilot]

So are power curve graphs a representation of the rpm at the Alternator Pulley?

If so, what elements do we have to know in order to work out the minimum Engine RPM we need to reach that optimum output?

I'm assuming that the size of the flywheel pulley, the belt circumference and the alternator pulley size are factors, but would appreciate any insight anyone can offer.

We will be spending a few days at anchor over the next month and a bit and I've not got around to putting any alternative charging sources onboard yet, so am depending on running the engine for a while to top up the batteries (I'm assured that for the amount of motoring we do, glazing isn't going to be an issue just yet).

Cheers, PT.

The ratio of the alternator RPM to engine RPM is simply the inverse of the ratio of the pulley diameters. So, if the engine pulley is twice the diameter of the alternator pulley, the alternator will spin at twice the engine RPM.

Of course, you must ensure that the alternator cannot go over 6,000 rpm at the engine maximum rpm.

 

[little_roundtop]

So are power curve graphs a representation of the rpm at the Alternator Pulley?

If so, what elements do we have to know in order to work out the minimum Engine RPM we need to reach that optimum output?

I'm assuming that the size of the flywheel pulley, the belt circumference and the alternator pulley size are factors, but would appreciate any insight anyone can offer.

We will be spending a few days at anchor over the next month and a bit and I've not got around to putting any alternative charging sources onboard yet, so am depending on running the engine for a while to top up the batteries (I'm assured that for the amount of motoring we do, glazing isn't going to be an issue just yet).

Cheers, PT.

Ah, now that I can't help with. It's pretty obvious though that if peak output from your alternator is at 6000rpm it's talking about alternator rpm, 'cause your diesel engine won't get anywhere near that.

Edit: I've just looked at the service manual for my Yanmar engine and alternator. The power output graphs are labelled with "speed of alternator".

 

[crisjones]

The alternator speed to engine speed ratio is directly related to the crankshaft and alternator pulley diameters. So if the crankshaft pulley is twice the diameter of the alternator pulley then the alternator will rotate twice as fast as the engine. This will probably be somewhere near the ratio you will have, most diesels have a max rev of 3 - 4 000 so if your engine revs to 3000 then your alternator would then be at 6000.

The diameter you should use for calculations is the "effective" pulley diameter which is around the middle of the belt, however if you just measure the outside diameter of both pulleys it will give you a close enough answer for what you are trying to find.

As others have said external charge controllers cannot increase the max output of an alternator, what they do is increase the charge voltage as the batteries become nearer to fully charged, this makes the batteries accept more charge in the 80 - 100% of full charge area. So if your batteries are 50% discharged then a standard alternator with a standard regulator will put as much amperage into the batteries as the same alternator with an external regulator, it is only as battery voltage rises that external regulators make a difference.

However it is generally still worth fitting an external regulator because they do make sure the batteries get to 100% as quickly as possible and they usually incorporate some form of temperature compensation that also improves the charging efficiency.

The only way to get more amperage is to fit a bigger output alternator.

Also you should bear in mind that alternators are less efficient as they get hotter so actual output will again be less than the theoretical output. The confined spaces of most boat engine bays means that temperatures can get much higher than you might think, and even more so around the alternator because there will not be that much airflow around the engine bay, even allowing for the fan built into the alternator. The temperature of a boat engine alternator will certainly be much higher than that used for the output graph you are looking at!!!!

 

[dt4134]

Hi All, I have been looking at the performance of my 60 amp alternator and see that it has to run at 6000rpm to achieve 62 amps @13.5 volts.

How big is your battery bank?

I've two 181Ah batteries and the most I've seen being driven into them is 49A across the combined bank. That was with a Sterling A to B charger fitted and it soon dropped off as the batteries charged.

 

[rigpigpaul]

Thanks All for your advice. I want to eventually fit an inverter and also increase the size of my battery bank. I have been doing a lot of motoring this summer so it seemed a shame not to use that power to charge a bigger battery bank. I have been averageing 2-3 hrs per day. As Chris Jones says 'only way to get more amperage is fit a bigger alternator'.
DT4134- I have two 140amp sealed batteries and I plan to add a third one.
rgds RPP

 

[Talulah]

'only way to get more amperage is fit a bigger alternator'.

We fitted a second alternator.

 

[dt4134]

DT4134- I have two 140amp sealed batteries and I plan to add a third one.
rgds RPP

It's harder to force extra current through sealed batteries as they generally won't take quite as high a voltage. The A-to-B charger has switches for you to configure the battery type and I think the recommended setting for sealed batteries is 14.4V.

I use 14.8V with unsealed batteries. Despite strong warnings in the manual about the higher voltage charging causing the batteries to consume water I've not had a problem.

It might be an idea to measure the current going into your two existing batteries to see whether you could usefully use extra output from the alternator even with three batteries.