Alternators

TiggerToo

TiggerToo

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I need to change the alternator on Tigger (VP MD2030B). Is there any point in considering changing the power of the alternator cfr what is already on there?
 
I think the original fit was a 60A alternator. You could fit a higher-output alternator, but don't go above about 90A or you'll have belt problems. To take full advantage of a larger alternator, you need a big battery bank - if your bank is less than, say, 400Ah, you won't see much benefit from a bigger alternator. One thing you should do is check the output curve of the alternator you plan to fit; getting one which has a good output at lower revs will help enormously. Prestolite alternators are quite good in this respect, if you're interested ask Adverc for advice (ADVERC BM | BATTERY MANAGEMENT SPECIALISTS), I got a Prestolite 90A alternator from them and they were very helpful.
 
I considered this a few years back when my alternator needed repair. I had the standard alternator for a Perk 4-107 .... which is not exactly a high powered job ... about 50A max ...

While the alternator was away being sorted - I sat down with pencil and paper - started writing down what I required with / without engine etc.

I found that my estimated engine hours exceeded easily by a 3x margin what was required with the standard alternator.

I am not suggesting to you that standard alternator is answer for you - what I am saying - is look at what you need against how many hours you expect to run engine and able to charge.
Often a better answer is to add larger battery or revise gear such as LED instead of filament lamps ... etc.
The main reason for swapping to a high rated alternator is the shorter charging time - as long as your battery management system allows the higher rates ?
 
Did the old one fulfill your needs? If so I can't see much point in buying one with higher O/P, but if you are upping your battery capacity because you have added more 'electricals' the it might be worth it. It also depends on the old ones O/P v the O/P and cost of the one you are thinking of.
 
I fitted a Mondeo alternator, higher output particularly at low rpm. £20 from a car breaker.
I wanted to charge hard and fast while motoring out of harbour before switching off the engine and sailing.
So I followed a similar thought process to Refueler, but got a different answer.
Yes it was a bit hard on belts, but they were cheap. Better management of soft-start charge control pretty much solved that anyway.

Some 50A boat alternators are only 50A at max revs.
If it's only <30A at tickover and you're putting several A into the fridge and some into the engine battery.... do the maths for your own scenario, we're all different.
 
lw395 said:
I fitted a Mondeo alternator, higher output particularly at low rpm. £20 from a car breaker.
I wanted to charge hard and fast while motoring out of harbour before switching off the engine and sailing.
So I followed a similar thought process to Refueler, but got a different answer.
Yes it was a bit hard on belts, but they were cheap. Better management of soft-start charge control pretty much solved that anyway.

Some 50A boat alternators are only 50A at max revs.
If it's only <30A at tickover and you're putting several A into the fridge and some into the engine battery.... do the maths for your own scenario, we're all different.
Click to expand...

Interesting point that - many people forget that output is dependent on how high charged battery is.

Its not only rpm of the alternator. BUT why we use alternators now instead of generators - alternators produce better rates over a wider range of rpm. In fact producing good output at moderate rpm.
 
pvb said:
I think the original fit was a 60A alternator. You could fit a higher-output alternator, but don't go above about 90A or you'll have belt problems.
Click to expand...
Swapped the 60A for a 90A on my MD2020B, worked well and happy with the extra output, purchased from here .: Starter Motor & Alternator Company :. good advice over the phone, advised on pulley size to maximise output at cruising revs, said the same as PVB in that higher than 90A is not recommended/possible.
 
OP needs to change his alternator. It may be OK to replace witha higher powered one but will not necessarily change anything and may invite problems of mounting belts etc. . As asked before is the standard alternator not doing the job? Actually I would ask why replace the alternator. They are very seldom damaged beyond repair. Almost certainly cheaper and easier to get the old one fixed by an auto electrician. ol'will
 
I don't know if still possible - but in the past - some alternators had optional belt pulleys to change rpm range ..... and some could be purchased for retro-fit. Basically to bring the alternator up in rpm against a lower engine speed.

I think for many boaters who don't do much more than weekend sailing ... maybe odd week long cruises - is the change really needed ? I can see it for the more serious boaters ...

I do 10 - 14 day cruises in Baltic and my 50A with two 90 A/Hr batterys do well ... I accept that my engine runs maybe 2x the amount of a non motor-sailer and I don't have too many mod-cons on board - but still its more than enough.
Its all about knowing what you have and managing resources. ie Fitting the relay for my coolbox made a big difference ... that baby draws up to 9A continuous - may not sound much ... but do the maths.
 
TiggerToo said:
I need to change the alternator on Tigger (VP MD2030B). Is there any point in considering changing the power of the alternator cfr what is already on there?
Click to expand...
Hard to say without more info about battery bank size & normal use, & what voltage the existing alternator regulator is. If your bank isn't huge and doesn't get discharged to very low then good chance a bigger alternator won't make much difference - the batteries will only accept what they decide so hooking up a power station won't change much to that.

This based on AGMs but principle is the same >
How Fast Can an AGM Battery be Charged?

Older alternators may well have a regulator set to below 14v, that will take forever to get your batts back to full charge..
 
Refueler said:
Interesting point that - many people forget that output is dependent on how high charged battery is.

Its not only rpm of the alternator. BUT why we use alternators now instead of generators - alternators produce better rates over a wider range of rpm. In fact producing good output at moderate rpm.
Click to expand...
Being more specific, there were a lot of times with my original alternator when it wasn't running at its voltage limit. Typical use pattern included often motoring fairly slowly through mooring areas, motoring at a steady speed to get out of the harbour, then motoring slowly again while hoisting sails.
It's easy to get behind with charging when the above is repeated for a few days on a fortnight's cruise.
Even with a pretty small battery bank, I had 220Ah at the time, at 50% charged, it's not unreasonable to want to shove in more than 50A initially, plus some for the engine battery, some for the fridge etc.With the right alternator you can do this while motoring through the moorings at 1000rpm making no wash, or while just holding the boat steady while hoisting the main.
 
lw395 said:
Being more specific, there were a lot of times with my original alternator when it wasn't running at its voltage limit. Typical use pattern included often motoring fairly slowly through mooring areas, motoring at a steady speed to get out of the harbour, then motoring slowly again while hoisting sails.
It's easy to get behind with charging when the above is repeated for a few days on a fortnight's cruise.
Even with a pretty small battery bank, I had 220Ah at the time, at 50% charged, it's not unreasonable to want to shove in more than 50A initially, plus some for the engine battery, some for the fridge etc.With the right alternator you can do this while motoring through the moorings at 1000rpm making no wash, or while just holding the boat steady while hoisting the main.
Click to expand...

I agree mostly with you ..

Its a point that one main reason for the change from Generator to Alternator - was the ability to have decent output at low rpm.

The trick is get the alternator set for the expected use of engine. In the old days - you could swap out the belt pulley to change the ratio of engine to alternator rpm. I don't know if that's possible still today ?
 
Refueler said:
The trick is get the alternator set for the expected use of engine. In the old days - you could swap out the belt pulley to change the ratio of engine to alternator rpm. I don't know if that's possible still today ?
Click to expand...

This is what I did with a similar (MD2020B) engine.
 
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