Battery Fault single alternator - SPLIT from original

[Ianmc]

Ive a single 70amp alternator charging 3 battery's I've check charge and very low,is it possible to change to a 110amp alternator.

[nicknorman]

15 minutes ago, Ianmc said:

Ive a single 70amp alternator charging 3 battery's I've check charge and very low,is it possible to change to a 110amp alternator.

The problem is that larger alternators cannot really be driven by a standard V belt as the belt isn't capable of transferring that much power - it will slip. 110A is on the cusp of that and is probably a bit too much although it depends on the size of the pulleys. Perhaps it would be better to make sure you are getting the best out of the 70A alternator. In other words, that it is working properly (no blown diodes reducing output), that the wiring is transferring the current to the batteries without dropping much voltage and that you are running the engine fast enough to spin the alternator fast enough to produce its full output. If all those are good you could consider an alternator controller such as an Adverc or a Sterling A2B

Electricity is invisible and so you need adequate monitoring equipment, do you have some sort of battery monitor, or at least a multimeter, preferably a DC clamp meter? Without some monitoring equipment, you are working in the dark.

Edited November 22, 2017 by nicknorman

[ditchcrawler]

31 minutes ago, Ianmc said:

Ive a single 70amp alternator charging 3 battery's I've check charge and very low,is it possible to change to a 110amp alternator.

If the charge is low a bigger one wont help, you need to find out why its low and also what you mean by low, Low current , volts or what.

[Tony Brooks]

This is not intended as a pop at you but is intended to help less technical members get correct and prompt relies.

If we had been told this was a single alternator boat in the first post the most likely reply as per Nick's implication - one or more blown diodes - would have been conveyed to you at 19.14 on Monday rather than the totally useless info I did give to try to elicit more info.

I echo what Nick says about single V belts and big alternators. I would set an absolute maxim,um size for a quality 10mm ish V belt as 90 amps.

Blow diodes will give a low charge and also either an excessive or low charging voltage.

30 minutes ago, Ianmc said:

Ive a single 70amp alternator charging 3 battery's I've check charge and very low,is it possible to change to a 110amp alternator.

I think that you need to check voltdrop along all the charging circuit and ensure the charge splitting is efficient and in good fettle.

1. Unless its a zero voltdrop design a split charge diode is bad news and needs to go.

2. 1, 2, both & off switches are not that robust so can end up causing excessive voltdrop. I would not have one or ever fit one.

3. Ensure the main charging lead (B+) is of adequate size AND runs direct to the DOMESTIC battery. (After rewiring to get rid of a split charge diode/switch).

Now to test voltdrop. Engine batteries spend all/most of their time all but fully charged so concentrate on the domestics first.

NOTE - this is hard to do if the alternator is faulty and down on amps.

Extend one lead of a voltmeter (normally set to 20V DC) and connect it between the alternator B+ and the battery positive, ideally the lead post/stud NOT the clamp. Ignore whet the meters reads. Put  a load of lights and pumps on, start and rev the engine. with the alternator output as high as you can get it read the voltage. If it is much more than about 0.3 volts you have excess voltdrop and need to trace it by stepping the battery end of the meter lead back through the circuit. maybe to Bat side of the master switch, the other side of the master switch, if the main charging current is routed through the charge splitter then more readings on each side if its big terminals. That should identify the source of the voltdrop when the meter suddenly reads much lower. If there is a gradual drop at each place then its probably undersized cables.

Now repeat between the B- alternator terminal if the alternator has one and battery negative. If there is no battery negative then use the alternator case. Repeat teh above procedure by stepping back through the negative circuit BUT I would not want to see much more than 0.1V of voltdrop on it.

Remember every 0.1V of voltdrop makes a very big difference to the rate of battery charge  at high charging currents.

 

 

 

 

 

[WotEver]

One more thought not mentioned so far - the extra 40A from a 110A alternator wouldn’t actually reduce the charge time that much unless the bank is very large and even then not by very much. 

2 hours ago, nicknorman said:

you could consider an alternator controller such as an Adverc or a Sterling A2B

Something not mentioned on this forum very often is how much an external controller might stress what is effectively a car alternator. The alt was designed to give a high output for a short while to top up the starter battery. It’s alteady working harder than ‘normal’ by recharging domestic batteries. Making it work harder still for hours on end will undoubtedly shorten its life. 

Edited November 22, 2017 by WotEver

[nicknorman]

Tony B and Nibbly, did you notice that the recent post about the single alternator was from a different person from the OP? Separate issue.

47 minutes ago, WotEver said:

One more thought not mentioned so far - the extra 40A from a 110A alternator wouldn’t actually reduce the charge time that much unless the bank is very large and even then not by very much. 

Something not mentioned on this forum very often is how much an external controller might stress what is effectively a car alternator. The alt was designed to give a high output for a short while to top up the starter battery. It’s alteady working harder than ‘normal’ by recharging domestic batteries. Making it work harder still for hours on end will undoubtedly shorten its life. 

Yes I’m sure this is true, the question is by how much? It might be worth say reducing the alternator life from 10 years to 5 years if it meant the batteries were getting properly charged with less engine running time. A replacement bog standard 70A alternator is pretty cheap.

[magpie patrick]

Please note - this has been split from another topic here

Battery fault original post

I may not have done it perfectly, if anything is astray please let us know

[ditchcrawler]

1 hour ago, magpie patrick said:

Please note - this has been split from another topic here

Battery fault original post

I may not have done it perfectly, if anything is astray please let us know

Well done, I could see it causing problems.

[OldGoat]

7 hours ago, Tony Brooks said:

This is not intended as a pop at you but is intended to help less technical members get correct and prompt relies.

If we had been told this was a single alternator boat in the first post the most likely reply as per Nick's implication - one or more blown diodes - would have been conveyed to you at 19.14 on Monday rather than the totally useless info I did give to try to elicit more info.

I echo what Nick says about single V belts and big alternators. I would set an absolute maxim,um size for a quality 10mm ish V belt as 90 amps.

Blow diodes will give a low charge and also either an excessive or low charging voltage.

I think that you need to check voltdrop along all the charging circuit and ensure the charge splitting is efficient and in good fettle.

1. Unless its a zero voltdrop design a split charge diode is bad news and needs to go.

2. 1, 2, both & off switches are not that robust so can end up causing excessive voltdrop. I would not have one or ever fit one.

3. Ensure the main charging lead (B+) is of adequate size AND runs direct to the DOMESTIC battery. (After rewiring to get rid of a split charge diode/switch).

Now to test voltdrop. Engine batteries spend all/most of their time all but fully charged so concentrate on the domestics first.

NOTE - this is hard to do if the alternator is faulty and down on amps.

Extend one lead of a voltmeter (normally set to 20V DC) and connect it between the alternator B+ and the battery positive, ideally the lead post/stud NOT the clamp. Ignore whet the meters reads. Put  a load of lights and pumps on, start and rev the engine. with the alternator output as high as you can get it read the voltage. If it is much more than about 0.3 volts you have excess voltdrop and need to trace it by stepping the battery end of the meter lead back through the circuit. maybe to Bat side of the master switch, the other side of the master switch, if the main charging current is routed through the charge splitter then more readings on each side if its big terminals. That should identify the source of the voltdrop when the meter suddenly reads much lower. If there is a gradual drop at each place then its probably undersized cables.

Now repeat between the B- alternator terminal if the alternator has one and battery negative. If there is no battery negative then use the alternator case. Repeat teh above procedure by stepping back through the negative circuit BUT I would not want to see much more than 0.1V of voltdrop on it.

Remember every 0.1V of voltdrop makes a very big difference to the rate of battery charge  at high charging currents.

 

 

 

 

 

On a point of information (bearing in mind this type of thread is becoming more frequent...) - would it improve matters somewhat / not at all if a cogged belt was fitted instead of a plain variety?

If so, what would that capacity be (in general)?

I used cogged belts on a much bigger installation (as it happens 145 amps @24v) with success - but such success was to make the belts last many times longer. A better solution is the fitting of flat multi row belts - but that's a whole new topic.

Sometimes there's no easy solution - but folks are often not able to accept that fact.... 

 

 

[ditchcrawler]

34 minutes ago, OldGoat said:

 s it happens 145 amps @24v) with success - but such success was to make the belts last many times longer. A better solution is the fitting of flat multi row belts - but that's a whole new topic.

Sometimes there's no easy solution - but folks are often not able to accept that fact.... 

 

 

That's over 5 hp.

[nicknorman]

1 hour ago, OldGoat said:

On a point of information (bearing in mind this type of thread is becoming more frequent...) - would it improve matters somewhat / not at all if a cogged belt was fitted instead of a plain variety?

If so, what would that capacity be (in general)?

I used cogged belts on a much bigger installation (as it happens 145 amps @24v) with success - but such success was to make the belts last many times longer. A better solution is the fitting of flat multi row belts - but that's a whole new topic.

Sometimes there's no easy solution - but folks are often not able to accept that fact.... 

 

Wow 145A at 24v sounds like a huge alternator! I think a cogged belt helps, but your question can’t easily be answered because it so much depends on pulley diameter. Bear in mind that the power transferred is a function of belt pull, which has a limit because of belt slip, multiplied by belt speed which has a limit because the repeated bending around the pullies generates frictional heat. 

A smallish crank pulley driving a tiny alternator pulley will struggle due to belt pull causing slip.

A huge crank pulley driving a medium sized alternator pulley will have much less belt pull but might hit limiting belt speeds / belt temperature.

There is a compromise to be struck but because canal boats generally have their engines running routinely at the low end of their rev range, there needs to be a big pulley ratio which, keeping the crank pulley within reasonable dimensions, means the alternator pulley is small and thus suffers from a propensity to slip.

So I think all that means there is no answer to your question! But generally, increasing the alternator power means you are departing from the designer’s ideas and entering territory away from the optimum compromise, unless you also change the crankshaft pulley to match.

[Tony Brooks]

In simple terms I understand a cogged belt is used to allow it to RELIABLY drive on smaller pulley diameters than a plain belt so thinking that fitting one allows you to drive a larger alternator is probably incorrect. unless the pulley diameter was too small but that is a pulley problem, not a belt one.

If you want to drive a high output alternator then you need a wide  polly-V belt or twin normal V belts.

[ditchcrawler]

I am still not sure what the OP means by very low, If he is not getting full output from a 70 Amp unit I don't see how 110 is going to help, unless he considers 70 amps low.

[nicknorman]

1 minute ago, ditchcrawler said:

I am still not sure what the OP means by very low, If he is not getting full output from a 70 Amp unit I don't see how 110 is going to help, unless he considers 70 amps low.

I rather get the feeling we’ll never know!

[WotEver]

@Ianmc any update to the questions posed in response to your post?

[Ianmc]

22 hours ago, nicknorman said:

The problem is that larger alternators cannot really be driven by a standard V belt as the belt isn't capable of transferring that much power - it will slip. 110A is on the cusp of that and is probably a bit too much although it depends on the size of the pulleys. Perhaps it would be better to make sure you are getting the best out of the 70A alternator. In other words, that it is working properly (no blown diodes reducing output), that the wiring is transferring the current to the batteries without dropping much voltage and that you are running the engine fast enough to spin the alternator fast enough to produce its full output. If all those are good you could consider an alternator controller such as an Adverc or a Sterling A2B

Electricity is invisible and so you need adequate monitoring equipment, do you have some sort of battery monitor, or at least a multimeter, preferably a DC clamp meter? Without some monitoring equipment, you are working in the dark.

I'm not doing the work I've got this guy who says I need a bigger amp alternator I've no idea about electrics,I don't want to throw lots of money at this as I might be wasting my time,I've had the boat rewired,I've only got lights and pumps running off 2 leisure batteries and 1 engine starter battery running from a 70amp alternator I'm sure this would be ok,but this guy seams to think I need more power.

[nicknorman]

1 minute ago, Ianmc said:

I'm not doing the work I've got this guy who says I need a bigger amp alternator I've no idea about electrics,I don't want to throw lots of money at this as I might be wasting my time,I've had the boat rewired,I've only got lights and pumps running off 2 leisure batteries and 1 engine starter battery running from a 70amp alternator I'm sure this would be ok,but this guy seams to think I need more power.

Ok well he sounds a bit vague to me! Lots of people manage with a 70A alternator. As I said there can be a lot of variation in how much power you get out of an alternator mid-charge depending on its health and the health and suitability of the wiring. One would like to think that the latter is suitable and in good condition if it’s just been redone, but we’ve learnt on here to not necessarily trust “professionals”! Anyone can set themselves up as a “marine electrical engineer” with necessarily having any qualifications, experience or ability. Some are really good. Some are truly awful.

Anyway perhaps the answer is “if it ain’t broke don’t fix it!”? You could probably more easily fit a 90A alternator but the difference isn’t going to be much and I’m not sure it’s worth it especially if you’re not in a position to ensure your existing set up is working optimally.

[Tony Brooks]

If what you say is true then in my view your guy has seen you coming and is going to intentionally or unintentionally rip you off.

If your alternator is faulty then a larger one will solve the problem but so would one of the same size.

I run a 12V electric compressor fridge, lights, pumps, power a lap top, and charge phones from a single 70 amp alternator and until it broke I did it with a  60 amp one. Although I now have solar before that it was fine with about 4 hours or so running a day.  I would suggest this proves the guy is wrong.

Remember the time taken to fully charge a battery is fairly constant across a whole range of alternator outputs because after about half an hour or so (may well be less) its the batteries that decide how much charge they will take not the alternator. A larger one may get you to 80% charged noticeably faster but not fully charged.

If you do not want to throw loads of money at it then we need some accurate readings. Charging current with engine revving immediately after the first start of the day and charging voltage just before shut down at the end of the day. That should tell us if your alternator is faulty or not. At present it seems it may well be.

However its your money.

 

[cereal tiller]

21 hours ago, WotEver said:

One more thought not mentioned so far - the extra 40A from a 110A alternator wouldn’t actually reduce the charge time that much unless the bank is very large and even then not by very much. 

Something not mentioned on this forum very often is how much an external controller might stress what is effectively a car alternator. The alt was designed to give a high output for a short while to top up the starter battery. It’s alteady working harder than ‘normal’ by recharging domestic batteries. Making it work harder still for hours on end will undoubtedly shorten its life. 

That is the reason I put Temperature Limiters on all 3 Alternators.when the Stator Temp. reaches 75 C the Field is Switched off for 1-2 Minutes to allow a  cooling period,Charging then recommences.

Simple but Effective.

[Iain_S]

4 hours ago, Ianmc said:

I'm not doing the work I've got this guy who says I need a bigger amp alternator I've no idea about electrics,I don't want to throw lots of money at this as I might be wasting my time,I've had the boat rewired,I've only got lights and pumps running off 2 leisure batteries and 1 engine starter battery running from a 70amp alternator I'm sure this would be ok,but this guy seams to think I need more power.

As at least two experts have suggested, 70A should be plenty. 

Our 26' boat, Gamebird, has a 50A alternator, and that seldom works to capacity, due to the small(ish) crankshaft pulley on the Vetus M2 engine.