blowing up the alternator

[boatystuff]

hello

I am a new member and I've been lurking in the background for a bit but have decided to be bold and ask a stupid question. So here goes.

I have aquired a cheepy 2 stroke generator to charge the boat batteries. If I use it with the battery isolator open is it likely to damage the alternator? I think it will but would value other opinions

 

Boatystuff

[Keeping Up]

It's not likely to damage the alternator, whether the isolator is open or closed.

[steelaway]

hello

I am a new member and I've been lurking in the background for a bit but have decided to be bold and ask a stupid question. So here goes.

I have aquired a cheepy 2 stroke generator to charge the boat batteries. If I use it with the battery isolator open is it likely to damage the alternator? I think it will but would value other opinions

 

Boatystuff

 

Hi There

 

Have look here

 

Battery charging, from extrenal controller and Honda Generator & Sterling 1230CED

 

It was discussed last week

 

Alex

[blackrose]

Hi There

 

Have look here

 

Battery charging, from extrenal controller and Honda Generator & Sterling 1230CED

 

It was discussed last week

 

Alex

 

A cheap 2 stroke generator isn't going to produce the quality of sinewave required to run a Sterling 30amp Pro-Digital battery charger. I think Boaty was talking about charging direct from the generator's DC output.

 

I used to do this on my last boat and never even thought about damaging the alternator, but it's a fair question. The main problem you're going to have is that the direct DC output of your generator will probably only put out about 8 amps, so depending on the size of your battery bank it will take a long time to charge your batteries and will be highly inefficient in terms of fuel usage vs charge obtained (not to mention the racket you'll make with that genny).

 

For any serious battery charging you'd be much better off getting yourself a decent generator (like the Honda), with a pure sinewave AC output and combining this with a 3 stage battery charger as Alex has already alluded.

Edited February 15, 2008 by blackrose

[Dylan]

A cheap 2 stroke generator isn't going to produce the quality of sinewave required to run a Sterling 30amp Pro-Digital battery charger. I think Boaty was talking about charging direct from the generator's DC output.

 

I used to do this on my last boat and never even thought about damaging the alternator, but it's a fair question. The main problem you're going to have is that the direct DC output of your generator will probably only put out about 8 amps, so depending on the size of your battery bank it will take a long time to charge your batteries and will be highly inefficient in terms of fuel usage vs charge ratio.

 

For any serious battery charging you'd be much better off getting yourself a decent generator with a pure sinewave AC output and combining this with a 3 stage battery charger as Alex has alluded to.

I echo what you say about the pro-digital series of charger. Sterling advised me to use the Sterling "Universal" type charger for generator use rather than the pro digital, and it works fine even off the crude frame generator. As mentioned recently, my 40amp version struggles off an 800VA genny, but evidence suggests that the new improved version should be OK.

[blackrose]

I echo what you say about the pro-digital series of charger. Sterling advised me to use the Sterling "Universal" type charger for generator use rather than the pro digital, and it works fine even off the crude frame generator. As mentioned recently, my 40amp version struggles off an 800VA genny, but evidence suggests that the new improved version should be OK.

 

I guess the Pro-Digital series must be a bit more sensitive than the Universal type. My 30amp pro-digital works fine from my Honda EU10i suitcase generator.

[steelaway]

I guess the Pro-Digital series must be a bit more sensitive than the Universal type. My 30amp pro-digital works fine from my Honda EU10i suitcase generator.

 

Hi There

 

I am still struggling to understand the advantage of seperate generators and chargers.

We all have a 60 to 110 amp charger fastened to the diesel fueled boat engine.

I realise it seems a bit of an over kill to run 30plus Hp for charging the batteries but you can have free hot water as well.

With a charge controler you will get the full output of the alternatorand full battery's

I hope this dosn't upset any one - its not meant to.

 

Alex

[magnetman]

My mate has a 650 hour old Beta 2203 diesel engine on his very comfortable widebeam, with a 145amp domestic alternator which has just stopped working. It seems it may be difficult to get parts due to the alternator being a slovenian made copy of a Bosch. I think around about this point he may be thinking how handy it would be to have a decent genny setup... Eggs in 1 basket?

[Lesd]

My mate has a 650 hour old Beta 2203 diesel engine on his very comfortable widebeam, with a 145amp domestic alternator which has just stopped working. It seems it may be difficult to get parts due to the alternator being a slovenian made copy of a Bosch. I think around about this point he may be thinking how handy it would be to have a decent genny setup... Eggs in 1 basket?

 

Completely agree on this point. Our engine was out of action for 3-4 days in December, it was our only source of power generation and as live aboards it got a little uncomfortable lol. I'm looking at the Honda option hen funds permit.

Edited February 15, 2008 by Lesd

[bottle]

Have to agree, have tried to spec at least two ways of doing everything on our boat.

[steelaway]

Have to agree, have tried to spec at least two ways of doing everything on our boat.

 

Hi there

 

Yes now I can see your piont of 'Belt and Braces'

 

Alex

[blackrose]

Hi there

 

Yes now I can see your piont of 'Belt and Braces'

 

Alex

 

Also Alex, even with an external regulator (charge controller) you still don't get the full output of your alternator (at least I don't, and perhaps Chris W will be along to wow us with some more maths to explain this shortly ).

 

The other thing is that a good generator is a lot quieter than a diesel boat engine, which although soft mounted can vibrate the whole boat.

 

Lastly, I'd rather have a lot of engine hours on my generator than on my engine. One cost me £600, the other cost £6000.

 

*That's not to say there aren't disadvantages to suitcase generators too - bringing petrol on board being the main one.

Edited February 15, 2008 by blackrose

[Dylan]

Also Alex, even with an external regulator (charge controller) you still don't get the full output of your alternator (at least I don't, and perhaps Chris W will be along to wow us with some more maths to explain this shortly ).

 

The other thing is that a good generator is a lot quieter than a diesel boat engine, which although soft mounted can vibrate the whole boat.

 

Lastly, I'd rather have a lot of engine hours on my generator than on my engine. One cost me £600, the other cost £6000.

 

*That's not to say there aren't disadvantages to suitcase generators too - bringing petrol on board being the main one.

I agree with most of that, save to say that we do get hot water from the prop. engine. It is clocking up hours on the prop. engine that concerns me. Economy could be an issue when we know for certain what our diesel will cost in November. Eventually I plan to fit a Morco, and use the genny for all "moored" charging, keeping the prop. engine for its intended purpose. I will of course have "free" hot water when cruising. I may well be wrong on all of these points, but feel comfortable with it.

[chris w]

Also Alex, even with an external regulator (charge controller) you still don't get the full output of your alternator (at least I don't, and perhaps Chris W will be along to wow us with some more maths to explain this shortly ).

 

I've risen to the bait....................

 

Firstly, you will not damage the alternator by using a generator because an alternator's output is isolated with some very beefy diodes - so no worries.

 

Secondly, Blackrose is absolutely correct. You will only ever get a maximum of about 60-65% of the alternator's nominal output at NB engine revs assuming the engine/alternator pulley ratio is the usual 2:1. So an 80A alternator will give out a maximum of around 50A at typical NB revs.

 

An external alternator controller will NOT increase the available maximum current but it will deliver this maximum current for far longer than the alternator's internal regulator ad hence charging time is significantly reduced.

 

Chris

[boatystuff]

Thanks one and all for your comments

 

It has given me some food fort hought.My original reasons for aquiring the generator were two fold. 1) it was free and 2) I need to run some small power tools as I am painting the boat this year.The battery charging was a secondary thought as the generator has a12v dc outlet.Its nice to no I wont be damaging the alternator

 

Boatystuff

[chris w]

..................The battery charging was a secondary thought as the generator has a12v dc outlet.Its nice to no I wont be damaging the alternator

 

Boatystuff

 

But don't use the 12v outlet for battery charging. The current is way too small (8A) and it is not meant for charging domestic batteries only car (engine start) battereis). It will not condition your domestics correctly. Use the gennie to power a proper multistage mains charger.

 

Chris

[Dylan]

There have been lots of inquiries lately about using gensets to charge batteries, and with the probable forthcoming hike in diesel prices I expect there will be more. I wondered if anybody had tried these budget chargers from Argos and whether they would be suitable for those with gensets?

 

http://www.argos.co.uk/static/Product/part...htm#producttabs

[chris w]

There have been lots of inquiries lately about using gensets to charge batteries, and with the probable forthcoming hike in diesel prices I expect there will be more. I wondered if anybody had tried these budget chargers from Argos and whether they would be suitable for those with gensets?

 

http://www.argos.co.uk/static/Product/part...htm#producttabs

 

 

I just looked up the spec on the Black & Decker website ( clicky here and, on the face of it, it does seem that it is a 3 stage charger with selection for gel, AGM or wet lead-acid and a maximum charge current of 30A. (The 80A setting is for putting a very rapid charge into an engine start battery).

 

It doesn't mention any ability to be used as a power pack, once the batteries are charged, so I would assume it cannot play this role and I would want to check the charging voltages (ie: I would want 14.8v on my wet lead acids). But for only £80 it does seem that it has its uses.

 

However, if you need one of these, why not buy a proper, software controlled multi-stage mains charger/power pack? The gennie can supply the 240v to run it. The power pack facility means that all the time you are connected to a shoreline, or a gennie, your batteries are not being used and all (12v) power is being supplied by the gennie or shoreline.

 

Chris

[Dylan]

I just looked up the spec on the Black & Decker website ( clicky here and, on the face of it, it does seem that it is a 3 stage charger with selection for gel, AGM or wet lead-acid and a maximum charge current of 30A. (The 80A setting is for putting a very rapid charge into an engine start battery).

 

It doesn't mention any ability to be used as a power pack, once the batteries are charged, so I would assume it cannot play this role and I would want to check the charging voltages (ie: I would want 14.8v on my wet lead acids). But for only £80 it does seem that it has its uses.

 

However, if you need one of these, why not buy a proper, software controlled multi-stage mains charger/power pack? The gennie can supply the 240v to run it. The power pack facility means that all the time you are connected to a shoreline, or a gennie, your batteries are not being used and all (12v) power is being supplied by the gennie or shoreline.

 

Chris

I agree Chris, and ours is a Sterling charger. I just saw this item and wondered if it would be any help to those who are struggling. If it is genuinely what it claims to be, then £80 doesn't seem bad for a 30Amp charger.

[Bob the welder]

hi! Please could someone tell me what rpm should a boat alternator run at for maximum charging capacity?

Yours hopefully,

Bob the Welder.

[Lesd]

Hi Bob,

No doubt you'll get some more technical answers but my understanding is that the answer to your quetion will vary according to the specifics of your installation, and that the only way to tell will be to measure the output current as you increase engine revs to find the optimal revs. I think one key issue in this is the pully ratio. On our boat we are lucky to get max current at tick over (just under 900rpm) but some say they see the max current at 1200 or 1400 rpm. You really need an ameter to check !

Hope this helps a little

Les

[Dylan]

I am working from memory ( ) but I am certain that the graph for my particular alternator starts to level off at around 4000 revs. My pulleys are 2:1 so this would mean 2000 rpm at the crankshaft. It does however give a very respectable output (measured) at 1200rpm engine speed. It will vary for different alternators and I agree with the other poster that an ammeter is vital in order to measure the output.

Edited February 17, 2008 by Dylan

[steelaway]

Hi There

 

I seem to able to tell by the volt meter. If I take the revs from tickover to around 1500rpm, I can see the volts rise to 14+. I can the back of to about 1200rpm and it stays at 14+. I guess you have to 'excite' the alternator and it then remains at charge at lower revs.

 

Alex

[chris w]

Hi There

 

I seem to able to tell by the volt meter. If I take the revs from tickover to around 1500rpm, I can see the volts rise to 14+. I can the back of to about 1200rpm and it stays at 14+. I guess you have to 'excite' the alternator and it then remains at charge at lower revs.

 

Alex

 

Actually you can't tell from the voltage, which relates to the battery terminal voltage. You could be putting maximum amps into the battery from the alternator but the voltage could still be reading only 13.5v. The only true way is to measure the amps. The reason the voltage stays the same when you back off the revs is nothing to do with "exciting" the alternator (that's a totally different phenomenon). It's due to the fact that the high revs (ie: high current) raised the battery terminal voltage as the battery gulped up the charge. Revving back will lower the current but not the battery terminal voltage.

 

Most alternators will be giving close to maximum output at around 5000rpm which, on a standard 2:1 pulley ratio, means an engine speed of 2500rpm which is way above normal running speeds on a NB.

 

That's why, whatever the nominal alternator output, say 80A, you will only get about 60% of that (say 50A) at typical NB engine revs. It also means that if you have a low output alternator (nominally 55A say), the maximum current will only be around 30-35A on a NB. This maximum current will only be for a relatively short time too, unless you have an external alternator controller fitted. The external controller can't increase the maximum current possible, due to rev limiting, but it can and does increase the time for which that current is on maximum.

 

Chris

Edited February 18, 2008 by chris w

[oldade]

Actually you can't tell from the voltage, which relates to the battery terminal voltage. You could be putting maximum amps into the battery from the alternator but the voltage could still be reading only 13.5v. The only true way is to measure the amps. The reason the voltage stays the same when you back off the revs is nothing to do with "exciting" the alternator (that's a totally different phenomenon). It's due to the fact that the high revs (ie: high current) raised the battery terminal voltage as the battery gulped up the charge. Revving back will lower the current but not the battery terminal voltage.

 

Most alternators will be giving close to maximum output at around 5000rpm which, on a standard 2:1 pulley ratio, means an engine speed of 2500rpm which is way above normal running speeds on a NB.

 

That's why, whatever the nominal alternator output, say 80A, you will only get about 60% of that (say 50A) at typical NB engine revs. It also means that if you have a low output alternator (nominally 55A say), the maximum current will only be around 30-35A on a NB. This maximum current will only be for a relatively short time too, unless you have an external alternator controller fitted. The external controller can't increase the maximum current possible, due to rev limiting, but it can and does increase the time for which that current is on maximum.

 

Chris

 

Hi

Can we get to the max output from the alternater by altering the pully ration

Ie making it 4: 1 ?

Or will we get problums with belts sliping etc ?

Thanks

ADE