High Volts or High Amps?

[Dave Taylor]

Our Sterling Alternator to Battery Charger died two weeks ago. Quite apart from the fact that it apparently cannot be replaced under warranty (don't go there!), I am now finding that it takes rather longer to get our large domestic battery bank up to decent charge. Not too surprising, as I have needed to revert to the standard arrangement with one 45 amp alternator feeding the starter battery and the other 175 amp alternator feeding the domestic bank. This is made up from former forklift truck cells, with a theoretical capacity (when new) of 1300 Amp-Hours (at the 5 hour discharge rate).

 

 

Decision time now:

Option 1) Go for another Sterling unit, which seemed to do an excellent job of charging the bank well and quickly, feeding potentially up to 220 amps to this massive bank. (Sterlings had OK'ed this connection, despite the fact that their unit is rated at 210 amp max.). Plus the alleged benefits of higher voltage as well as combined current. Concerns:- As we have had 2 of these units fail (first one under warranty), I don't want to repeat the process and get the same expensive result. My guess at the cause of failure (not confirmed by Sterling) is that heavy-ish use of the inverter whilst the charger was running may have drawn all those 220 amps through the charger and cooked it!

Option 2) Go for another way to combine the alternator outputs, but without enhancing voltage. SmartBank seems a good way forward if we choose this option, possibly with SmartGauge.

Option 3) Install some form of advanced alternator regulator to increase the charge voltage to 14.8 V or so. But Beta Marine confirm that their 175 amp Iskra alternators regulate between 14.4 and 14.8 volts anyway, so is there any point? (Yes, I have read Gibbo on this one, and others who insist that higher voltages from 3- or 4-stage digital alternator regulators really DO work !!)

Option 4) Leave it as it now is (basic manufacturer's setup) and suffer the longer charge times (and possible incomplete charging). Doesn't seem the best idea to me!

 

As I said, I have read Gibbo and others at some length, and am still faced with the question whether it would be better to combine the amps or enhance the volts, or both.

 

I am no expert, but managed the installation of the Sterling unit pretty well and am happy to tackle installation of a SmartBank or an advanced alternator regulator.

 

Thanks in anticipation of your advice!

 

Dave Taylor

[nb Innisfree]

Unless you spend a lot of time in bulk charge the loss of 45 amps from 220 amps won't make much difference.

 

You don't really know if Beta's figures are true, the only way to find out for sure is to wait until batts are nearing the end of the charge and check the alternator voltage.

Edited September 14, 2012 by nb Innisfree

[Dave Taylor]

Unless you spend a lot of time in bulk charge the loss of 45 amps from 220 amps won't make much difference.

 

You don't really know if Beta's figures are true, the only way to find out for sure is to wait until batts are nearing the end of the charge and check the alternator voltage.

 

True, I haven't yet put the multimeter on the alternator when the batteries are near full charge and there are no significant loads on - usually when we are charging (static), the inverter is on. Must try that soon!

 

Looking at the difference between 220 amps and 175 amps, it's the difference between 16.9% and 13.5% of the battery bank capacity. That means that charging at 220 amps provides just over 25% more charge than charging at 175 amps. Is that insignificant?

[nb Innisfree]

True, I haven't yet put the multimeter on the alternator when the batteries are near full charge and there are no significant loads on - usually when we are charging (static), the inverter is on. Must try that soon!

 

Looking at the difference between 220 amps and 175 amps, it's the difference between 16.9% and 13.5% of the battery bank capacity. That means that charging at 220 amps provides just over 25% more charge than charging at 175 amps. Is that insignificant?

 

When batteries finish bulk charge and enter absorption they will automatically reduce the charge so that loss of 45 amps is only significant while in bulk charge. Say you are charging from 50% state of charge batteries will take all that alternators can produce until about 80% SoC, that will happen quite quickly but as you say will take a bit longer due to loss of 45A alt, but from 80% to 100% will take many more hours at a lower charge rate and represents the majority of your charge sequence. So large charging capacity is then rendered useless.

 

If you practice partial state of charging i.e.only do a bulk charge with an occasional long full charge then the loss of 45 amps will be significant, but if you do most of your charging in absorption stage then that loss will be less significant.

 

ETA: Now nip over to the VP and get me a pint in.

Edited September 14, 2012 by nb Innisfree

[by'eck]

Our Sterling Alternator to Battery Charger died two weeks ago. Quite apart from the fact that it apparently cannot be replaced under warranty (don't go there!), I am now finding that it takes rather longer to get our large domestic battery bank up to decent charge. Not too surprising, as I have needed to revert to the standard arrangement with one 45 amp alternator feeding the starter battery and the other 175 amp alternator feeding the domestic bank. This is made up from former forklift truck cells, with a theoretical capacity (when new) of 1300 Amp-Hours (at the 5 hour discharge rate).

 

 

Decision time now:

Option 1) Go for another Sterling unit, which seemed to do an excellent job of charging the bank well and quickly, feeding potentially up to 220 amps to this massive bank. (Sterlings had OK'ed this connection, despite the fact that their unit is rated at 210 amp max.). Plus the alleged benefits of higher voltage as well as combined current. Concerns:- As we have had 2 of these units fail (first one under warranty), I don't want to repeat the process and get the same expensive result. My guess at the cause of failure (not confirmed by Sterling) is that heavy-ish use of the inverter whilst the charger was running may have drawn all those 220 amps through the charger and cooked it!

Option 2) Go for another way to combine the alternator outputs, but without enhancing voltage. SmartBank seems a good way forward if we choose this option, possibly with SmartGauge.

Option 3) Install some form of advanced alternator regulator to increase the charge voltage to 14.8 V or so. But Beta Marine confirm that their 175 amp Iskra alternators regulate between 14.4 and 14.8 volts anyway, so is there any point? (Yes, I have read Gibbo on this one, and others who insist that higher voltages from 3- or 4-stage digital alternator regulators really DO work !!)

Option 4) Leave it as it now is (basic manufacturer's setup) and suffer the longer charge times (and possible incomplete charging). Doesn't seem the best idea to me!

 

As I said, I have read Gibbo and others at some length, and am still faced with the question whether it would be better to combine the amps or enhance the volts, or both.

 

I am no expert, but managed the installation of the Sterling unit pretty well and am happy to tackle installation of a SmartBank or an advanced alternator regulator.

 

Thanks in anticipation of your advice!

 

Dave Taylor

 

Option 5 - Leave 175 amp alternator charging the domestic bank directly and fit a Sterling Pro split R zero-volt drop splitter (various configurations available but PSR122 probably most suitable) to the 45 amp alternator. As well as being a much cheaper option it will allow starter battery charge priority until 13.3 volts reached when domestic battery charging is brought on-line. Under conditions of heavy domestic load the unit will direct full charge current to that bank.

 

If used with an external alternator booster there is a dedicated sensing terminal on the unit to regulate both banks to same charge voltage.

[Eeyore]

Option 5 - Leave 175 amp alternator charging the domestic bank directly and fit a Sterling Pro split R zero-volt drop splitter (various configurations available but PSR122 probably most suitable) to the 45 amp alternator. As well as being a much cheaper option it will allow starter battery charge priority until 13.3 volts reached when domestic battery charging is brought on-line. Under conditions of heavy domestic load the unit will direct full charge current to that bank.

 

If used with an external alternator booster there is a dedicated sensing terminal on the unit to regulate both banks to same charge voltage.

Option 5a - just to prove its worth spending the money.

Fit a temporary battery isolator switch between the battery banks which can be used to parallel the batteries and alternators when running the engine. This is a cheap way of proving (or disproving) that simple paralleling can match the charging times you have experienced with the Sterling unit fitted.

I suspect that the charging time will be slightly longer, but not enough to justify the cost of another Sterling unit; in which case there have already been several suitable suggestions made by other contributors to the discussion.

Only use the switch with the engine running to avoid discharging the starter battery overnight.

Steve

Edited to add : Beta supplied Iskra 175 amp alternators have been supplied with 14.8 volt regulators.

Edited September 15, 2012 by Eeyore

[bottle]

One way to get nearer the stated outputs of the alternators (amps) is to spin them at about 6,000 rpm.

[smileypete]

Our Sterling Alternator to Battery Charger died two weeks ago. Quite apart from the fact that it apparently cannot be replaced under warranty (don't go there!), I am now finding that it takes rather longer to get our large domestic battery bank up to decent charge. Not too surprising, as I have needed to revert to the standard arrangement with one 45 amp alternator feeding the starter battery and the other 175 amp alternator feeding the domestic bank. This is made up from former forklift truck cells, with a theoretical capacity (when new) of 1300 Amp-Hours (at the 5 hour discharge rate).

Can you look up what voltage the forklift cells should be charged up to? Likely to be 14.8V for open/non sealed ones but there's no guarantees. Then measure what voltage the alt actually regulates up to, at the alt terminals, see if the internal regulator can be changed for something more suitable.

 

Once the charging voltage is sorted, next check the charge current just before the alt voltage reaches it's regulated level. If it's a lot less than 175A the alt pulley ratios may need alt-ering.

 

After that, when the alt is at full output compare voltage at alt output to voltage at batt terminals, to see if the wiring is dropping too much voltage.

 

Having done all that, then look at alt paralleling, Smartbank, zero drop splitters. But if the above sounds like too much hassle, why not just get another sterling box.

 

cheers, Pete.

~smpt~

Edited September 15, 2012 by smileypete

[Dave Taylor]

Thanks to everyone (so far!) for all your input.

 

I am learning a lot and it gives me much food for thought and fuel for eventual decisions.

 

When batteries finish bulk charge and enter absorption they will automatically reduce the charge so that loss of 45 amps is only significant while in bulk charge. Say you are charging from 50% state of charge batteries will take all that alternators can produce until about 80% SoC, that will happen quite quickly but as you say will take a bit longer due to loss of 45A alt, but from 80% to 100% will take many more hours at a lower charge rate and represents the majority of your charge sequence. So large charging capacity is then rendered useless.

 

If you practice partial state of charging i.e.only do a bulk charge with an occasional long full charge then the loss of 45 amps will be significant, but if you do most of your charging in absorption stage then that loss will be less significant.

 

Thanks, nb innisfree. I have now put the multimeter on each of the alternators after a shortish cruising day and find that they are each reading 14.3+ volts. Probably regulating at 14.4 volts, then, though Eeyore's comment below seems to back up Beta's figures of 14.4 to 14.8 volts.

 

Option 5 - Leave 175 amp alternator charging the domestic bank directly and fit a Sterling Pro split R zero-volt drop splitter (various configurations available but PSR122 probably most suitable) to the 45 amp alternator. As well as being a much cheaper option it will allow starter battery charge priority until 13.3 volts reached when domestic battery charging is brought on-line. Under conditions of heavy domestic load the unit will direct full charge current to that bank.

 

If used with an external alternator booster there is a dedicated sensing terminal on the unit to regulate both banks to same charge voltage.

 

Thanks, by'eck - completely fresh idea! I have had a good look at this option and compared with SmartBank - some pros and cons with each. If only one of the alternators has an external regulator and the 'sense' wire is connected as you (and Sterling) suggest, presumably that would mean that the alternator without external regulation would 'idle' once it reached its internally regulated voltage, leaving the externally regulated one to take the voltage up on its own?

 

Option 5a - just to prove its worth spending the money.

Fit a temporary battery isolator switch between the battery banks which can be used to parallel the batteries and alternators when running the engine. This is a cheap way of proving (or disproving) that simple paralleling can match the charging times you have experienced with the Sterling unit fitted.

I suspect that the charging time will be slightly longer, but not enough to justify the cost of another Sterling unit; in which case there have already been several suitable suggestions made by other contributors to the discussion.

Only use the switch with the engine running to avoid discharging the starter battery overnight.

Steve

Edited to add : Beta supplied Iskra 175 amp alternators have been supplied with 14.8 volt regulators.

 

Eeyore - Like the money-saving idea! Presumably the battery isolator would not need to be particularly high current rated, as we would be looking at chiefly the output of the 45 amp alternator travelling through it. Am I right here? Hope so, as I have a spare one, but can't remember its rating without digging it out.

 

I'm not sure whether your comment on Beta-supplied Iskra alternators means that they are all regulated at 14.8 volts, or that they can be supplied with 14.8 regulation. Please can you enlarge? Thanks.

 

One way to get nearer the stated outputs of the alternators (amps) is to spin them at about 6,000 rpm.

 

Yes, thanks for that, bottle. I am now looking at the pulley ratio question as well!

 

Can you look up what voltage the forklift cells should be charged up to? Likely to be 14.8V for open/non sealed ones but there's no guarantees. Then measure what voltage the alt actually regulates up to, at the alt terminals, see if the internal regulator can be changed for something more suitable.

 

Once the charging voltage is sorted, next check the charge current just before the alt voltage reaches it's regulated level. If it's a lot less than 175A the alt pulley ratios may need altering.

 

After that, when the alt is at full output compare voltage at alt output to voltage at batt terminals, to see if the wiring is dropping too much voltage.

 

Having done all that, then look at alt paralleling, Smartbank, zero drop splitters. But if the above sounds like too much hassle, why not just get another sterling box.

 

cheers, Pete.

~smpt~

 

Have not (yet) been able to check the proper charge voltage for these cells, Pete. Pretty sure you will be right; they are standard lead-acid cells. As they are 2 volt cells, obviously the voltage per cell will be 2.45 if there should be 14.8 across 6 of them. Hopefully I shall get an answer on this one soon - next week now!

 

 

I don't have any way of checking the charge current, but guess I might be able to borrow the appropriate kit if I decide to investigate this aspect more deeply. Meanwhile, I am looking at pulley ratios.

 

Cables are really nice and beefy, so voltage drop should be minimal. Made sure of that when fitting the Sterling box - all sorts of emphatic warnings from Sterling about undersized cables!!!

 

There's another good-looking option if I go for a SmartGauge - based system. Gibbo suggests a way to enhance alternator voltage here, with a neat way of dropping back to a lower 'float charge' voltage here. Has anyone tried this? If so, how easy is it to find the appropriate diodes - and then fit them?

 

Going right back to my original question . . . If I do decide to fit another Sterling A to B charger, I think I will only connect it to the 175 amp alternator, and just leave the starter alternator and battery to get on with their own thing!

[bottle]

I believe that Iskra (Beta) alternators will be regulated to 14.4v, to be on the safe side, as they do not know the type of batteries that will be fitted.

 

Mine is regulated to 28.8v, 24v system, which is OK as I have fitted AGM with a recommended charge voltage of 14.4v to 14.6v per battery.

[by'eck]

Thanks, by'eck - completely fresh idea! I have had a good look at this option and compared with SmartBank - some pros and cons with each. If only one of the alternators has an external regulator and the 'sense' wire is connected as you (and Sterling) suggest, presumably that would mean that the alternator without external regulation would 'idle' once it reached its internally regulated voltage, leaving the externally regulated one to take the voltage up on its own?

 

Even if both alternators have external regulators there will always be one that idles on light current demands from batteries. Not an issue at all though since when the batteries demand more and/or the load on them increases, they will both work hard together.

 

Needless to say I have a splitter (three way) on the smaller of my two alternators, the larger 160 amp one feeding the service bank directly. Although both have external DAR's its the 90 amp one that produces most current under light loads, attesting the efficiency of the splitter setup. I can actually hear how hard each is working since they both whine under load but with slightly different notes.

[Gibbo]

If your existing alternator is charging at 14.4 volts already, adding another A to B will do next to nothing. It might make a very marginal difference, but I doubt it would be enough to justify the cost on those grounds alone. Only you can decide whether x hundred pounds is value for money to get (say) a 2% reduction in charge time.

 

To find out whether paralleling in the other alternator will make any difference, the only real way is to discharge your batteries to the level they normally get discharged to, then recharge them in the way you normally do. And do it twice. Once with the alternators separated, once with them paralleled. Graph the voltage and current until you reach acceptance (it won't make any difference after that time so it's pointless recording the data). Compare them. That will tell you whether it's worth paralleling them. This is going to be dictated mainly by the condition of the batteries and pulley ratios on the alternators.

 

Don't try to time it between starting the charge and reaching acceptance because you won't really know what SoC you're starting from. But from the resultant voltage and current graphs you'll be able to make sure you're comparing apples with apples.

 

Don't try to connect and disconnect the other alternator during the charge to see what charge current difference it makes in order to try to do it one cycle. It will not work. You'll find you get an increase in charge current, but then it will reduce, and you'll have no way of knowing what it would have been if you hadn't done it. I've seen people do this and it results in nothing better than a coin toss or wild guess.

 

My gut feeling is that it won't make much difference with an alternator of that size unless you discharge your batteries really deeply.

[Eeyore]

duplicate post deleted

Edited September 16, 2012 by Eeyore

[Eeyore]

Thanks to everyone (so far!) for all your input.

 

I'm not sure whether your comment on Beta-supplied Iskra alternators means that they are all regulated at 14.8 volts, or that they can be supplied with 14.8 regulation. Please can you enlarge? Thanks.

Iskra once confirmed the regulator as 14.8 volts when I supplied their part number from an alternator fitted to a recent Beta 43. However their part number is unique to the product supplied to their customer, Beta Marine, so they didn't need to tell me. Beta did confirm the voltage at 14.8 volts, with a reminder that their maintenance schedule requires daily checking of battery electrolyte!

There is previous post on this subject here

Steve

[Dave Taylor]

I seem to be unable to post anything at the moment. Is there a general problem, or is it just me?

edited - seems to be OK now. Probably just me!

Edited September 16, 2012 by Dave Taylor

[Dave Taylor]

I believe that Iskra (Beta) alternators will be regulated to 14.4v, to be on the safe side, as they do not know the type of batteries that will be fitted.

 

Mine is regulated to 28.8v, 24v system, which is OK as I have fitted AGM with a recommended charge voltage of 14.4v to 14.6v per battery.

 

Thanks, bottle! You and Eeyore have given me two sides of the coin!

 

Iskra once confirmed the regulator as 14.8 volts when I supplied their part number from an alternator fitted to a recent Beta 43. However their part number is unique to the product supplied to their customer, Beta Marine, so they didn't need to tell me. Beta did confirm the voltage at 14.8 volts, with a reminder that their maintenance schedule requires daily checking of battery electrolyte!

There is previous post on this subject here

Steve

 

Thanks, Eeyore! You and bottle have given me both sides of the coin! I wonder whether Beta's reply to me was cautious in view of some of the adverse comments in the post you quoted? I am happy with either 14.4 or 14.8 volts . . .

 

Even if both alternators have external regulators there will always be one that idles on light current demands from batteries. Not an issue at all though since when the batteries demand more and/or the load on them increases, they will both work hard together.

 

Needless to say I have a splitter (three way) on the smaller of my two alternators, the larger 160 amp one feeding the service bank directly. Although both have external DAR's its the 90 amp one that produces most current under light loads, attesting the efficiency of the splitter setup. I can actually hear how hard each is working since they both whine under load but with slightly different notes.

 

Thanks! I now appreciate that there will always be one alternator idling as full charge approaches - no problem. I think paralleling in some form or other may be useful for me, especially for those times when we have discharged more deeply and need speedy recovery. Your setup sound good.

[Dave Taylor]

If your existing alternator is charging at 14.4 volts already, adding another A to B will do next to nothing. It might make a very marginal difference, but I doubt it would be enough to justify the cost on those grounds alone. Only you can decide whether x hundred pounds is value for money to get (say) a 2% reduction in charge time.

 

To find out whether paralleling in the other alternator will make any difference, the only real way is to discharge your batteries to the level they normally get discharged to, then recharge them in the way you normally do. And do it twice. Once with the alternators separated, once with them paralleled. Graph the voltage and current until you reach acceptance (it won't make any difference after that time so it's pointless recording the data). Compare them. That will tell you whether it's worth paralleling them. This is going to be dictated mainly by the condition of the batteries and pulley ratios on the alternators.

 

Don't try to time it between starting the charge and reaching acceptance because you won't really know what SoC you're starting from. But from the resultant voltage and current graphs you'll be able to make sure you're comparing apples with apples.

 

Don't try to connect and disconnect the other alternator during the charge to see what charge current difference it makes in order to try to do it one cycle. It will not work. You'll find you get an increase in charge current, but then it will reduce, and you'll have no way of knowing what it would have been if you hadn't done it. I've seen people do this and it results in nothing better than a coin toss or wild guess.

 

My gut feeling is that it won't make much difference with an alternator of that size unless you discharge your batteries really deeply.

 

Thanks, Gibbo! I hoped you might come in on this one. I can't do any current measuring at present, as I haven't got the necessary kit. Might be able to borrow it if I go into this in more detail.

 

The more I learn from this thread, the less likely I think I am to fit another A to B charger. Seems it wasn't doing as much as I thought it was! Presumably you would not advise me to consider the adaptations you have on your website to increase the alternator voltage 'on the cheap', even with the possibility of switching this boost off with your neat 'float' setup - ? I just want to make sure that these forklift cells don't die early from sulphation!

 

Thinking pulley ratios now, the crankshaft pulley is 170 mm diameter and the 175 amp alternator pulley is 75 mm diameter. This gives a ratio of 2.266667 : 1.

 

This gives the following alternator spin speeds:-

At tickover (800 rpm) 1800 rpm

At normal/fast cruising (1400 rpm) 3170 rpm

At absolute max speed (extreme manoeuvres!) (2000 rpm) 4530

 

Is there a way I can calculate the approximate current output for a given engine speed?

 

And how about an optimum stationary charging rpm, to give the best blend of economical engine running and optimal charging? Or is that just wishful thinking on my part?

 

Thanks again to everyone for all your help - the picture is beginning to come together!

[nb Innisfree]

Thinking pulley ratios now, the crankshaft pulley is 170 mm diameter and the 175 amp alternator pulley is 75 mm diameter. This gives a ratio of 2.266667 : 1.

 

This gives the following alternator spin speeds:-

At tickover (800 rpm) 1800 rpm

At normal/fast cruising (1400 rpm) 3170 rpm

At absolute max speed (extreme manoeuvres!) (2000 rpm) 4530

 

Is there a way I can calculate the approximate current output for a given engine speed?

 

And how about an optimum stationary charging rpm, to give the best blend of economical engine running and optimal charging? Or is that just wishful thinking on my part?

 

Thanks again to everyone for all your help - the picture is beginning to come together!

If you can try to fit as large an engine pulley as possible as this will enable an alt pulley to be reasonably large to increase belt wrap, a small alt pulley isn't an ideal setup as regards belt slip.

[Eeyore]

Thanks, Eeyore! You and bottle have given me both sides of the coin! I wonder whether Beta's reply to me was cautious in view of some of the adverse comments in the post you quoted? I am happy with either 14.4 or 14.8 volts . . .

Fork truck batteries are usualy quite tall, and for that and other reasons have a higher charging voltage. The gassing is in efect used to "stir" the electrolyte and maintain a uniform specific gravity across the surface of the plates. The exact charge voltage for your batteries will of course be in the manufacturers spec, which is very likely to be 14.8 volts or higher. A lower voltage is likely to shorten their remaining life. Gibbo and others will be able to provide a more indepth technical explaination if you need it. My own experience of taller batteries is on preserved 1950s diesel railcars (DMUs) which charge at 31.5 volts on a 24volt system, which is 15.75 volts across each 12 volt bank! (Stones 150 amp dynamo with Liliputt dual carbon pile regulators for those of you into regulator porn )

Edited September 16, 2012 by Eeyore

[Timleech]

 

 

Thinking pulley ratios now, the crankshaft pulley is 170 mm diameter and the 175 amp alternator pulley is 75 mm diameter. This gives a ratio of 2.266667 : 1.

 

 

 

If you're going to be that precise on ratios, best to get your facts straighter!

If you're measuring the outside diameters of the pulleys, the proper figure to use is the Pitch Diameter which is rather less. I'd have to look it up to be sure, but there's a fudge factor which from memory is about 10mm less than the OD for each pulley. Using that figure, as an example, your ratio would be 165/70 or 2.4:1.

 

Tim

[by'eck]

Thinking pulley ratios now, the crankshaft pulley is 170 mm diameter and the 175 amp alternator pulley is 75 mm diameter. This gives a ratio of 2.266667 : 1.

 

This gives the following alternator spin speeds:-

At tickover (800 rpm) 1800 rpm

At normal/fast cruising (1400 rpm) 3170 rpm

At absolute max speed (extreme manoeuvres!) (2000 rpm) 4530

 

 

Even re-calculating using Tim's advice your drive ratio seems a tad low.

 

Almost impossible to know what current a particular alternator would put out at various rpm without the manufacturer's spec sheet.

 

FWIW I have a little over 5:1 drive ratio and with clamp on meter measured 156 amps from a Leece Neville 160 amp alternator at just 650 rpm engine speed.

[smileypete]

Looks like there's a PDF on the Iskra website that gives the output over different RPM, though a shunt or DC clamp ammeter would be handy.

 

cheers, Pete.

~smpt~

[colin stone]

I use 57mm twin A belt pulleys on Leece Neville 24v 95A and 110A alternators and have no problem with slippage and engine pulley is 200mm. So just under 8k alt rpm at max engine rpm. Alt limit is 8k rpm, but car/auto derived alts can go to 15k+ rpm.

[Ryeland]

 

Thinking pulley ratios now, the crankshaft pulley is 170 mm diameter and the 175 amp alternator pulley is 75 mm diameter. This gives a ratio of 2.266667 : 1.

 

This gives the following alternator spin speeds:-

At tickover (800 rpm) 1800 rpm

At normal/fast cruising (1400 rpm) 3170 rpm

At absolute max speed (extreme manoeuvres!) (2000 rpm) 4530

 

Is there a way I can calculate the approximate current output for a given engine speed?

 

And how about an optimum stationary charging rpm, to give the best blend of economical engine running and optimal charging? Or is that just wishful thinking on my part?

 

Thanks again to everyone for all your help - the picture is beginning to come together!

 

My 100A Iskra alternator on a Beta 38 gives max output at about 1200rpm which would indicate that Beta have probably got the pulley ratios correct.

 

Richard

[Dave Taylor]

Fork truck batteries are usualy quite tall, and for that and other reasons have a higher charging voltage. The gassing is in efect used to "stir" the electrolyte and maintain a uniform specific gravity across the surface of the plates. The exact charge voltage for your batteries will of course be in the manufacturers spec, which is very likely to be 14.8 volts or higher. A lower voltage is likely to shorten their remaining life. Gibbo and others will be able to provide a more indepth technical explaination if you need it. My own experience of taller batteries is on preserved 1950s diesel railcars (DMUs) which charge at 31.5 volts on a 24volt system, which is 15.75 volts across each 12 volt bank! (Stones 150 amp dynamo with Liliputt dual carbon pile regulators for those of you into regulator porn )

 

Mmm . . . Yes, I have wondered about that. Our cells are tall. So, perhaps I should be trying to get 14.8 (+?) volts into them? One reason, perhaps, to consider Gibbo's neat approach to wire in a diode to raise the voltage (here) , along with a way to bypass it if the voltage rises too high (here). I have mentioned these before, but no comments so far - perhaps that means no-one has tried them? Maybe Gibbo will care to comment on the suitability of these mods to my situation? Much depends on whether my alternator is regulated to 14.4 or 14.8 volts. Seems to be at 14.4 but I probably need to go on checking for a few days in case the charge is just a bit down and the voltage has not had the chance to rise to full regulated value. Guess that such a large bank could slow down that rise. Something I did not know about when I got all those cells!