Alternator/battery problems

Csail

Csail

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Had problems starting engine so bought new battery, it started well for the first few times but is now flat so i reckon alternator is shot...this was the reply from Thornycroft so which option would you go for?

1) Replace existing 50 amp alternator with 70amp alternator. Supply new
70amp alternator/fan/pulley and new mounting bracket. Runs on existing
3/8" pullies & single 3/8" belt. 105.00 + vat = 123.38 Note. An increase in
fan belt wear/decreased fan belt life may be noticed with this option
and must be borne in mind.

2) Replace existing 50 amp alternator with 100amp alternator. Supply
new 100 amp alternator/fan/pulley , new mounting bracket, oversleeve
crankshaft pulley, new water pump pulley, new 1/2" belt. Runs on new single
1/2" drive pullies and belt. 195.00 + vat = 229.13

Carriage 12.50 + vat = 14.69
 
Being of a mean streak of mind I'd take the existing alternator along to the local auto-electrician and have him repair it.

If you get a replacement alternator, it's size should be governed by the total size of the battery bank it's charging. As you don't mention that it's difficult to give an opinion.

However, in my opinion:-

1. you'd do better to fit a smart regulator before considering changing the size of alternator.
2. consider the belt section and drive pulleys carefully, doubling the size of alternator will, in my experience, demand a different belt, at least and, possibly, a different pulley.

Get in touch with Adverc BM - they'll supply a genuine marine alternator as well as advise on regulation, at about 50-75% of the prices quoted in the marine market.

245, Trysull Road
Merry Hill
Wolverhampton WV3 7LG

tel 01902 380494

My contacts Trevor and Brian aren't into e-mail, being of a previous generation.
 
Its not the size of the alternator that matters. In fact if you were to output the full 70 amps to your batteries you would probably fry them! In practice it is the charging control circuit that is important. I would fit the smaller alternator and spend the extra pennies on a smart charger such as a Sterling. You might also find one more cheaply from an auto supplies shop. The majority of those fitted to Thornycroft engines will have a direct auto equivalent. It would also pay to check the wiring thoroughly before replacing the alternator. Are you sure you don't have a break or short somewhere? Does the little red light come on when you switch on? Does it go out when you run the engine? If either answer is no it might well be wiring.
 
The battery bank is controlled via a X split module.

If that's what I think it is it is a diode bridge that splits the charging between batteries. It is not a "smart charger". If it is in fact it will reduce the voltage somewhat at the battery itself which can be overcome by fitting a smart charger sensed at the battery or the output terminal of the splitter.
 
You can test the alternator on the bench, wire it up with a battery and a charging light and drive it with a power drill.
If it doesn't lift the battery voltage to 14+, then investigate further.
If the bulb doesn't light properly, check the brushes.
If everything appears sound check rectifier and regulator modules.
Non charging may also be caused by a wiring fault, or your x-split module, so its worth verifying that the alternator is the problem.
Depending on how much motoring you do, the output of your alternator may be well adequate. If you want to upgrade cheaply, see if you can fit a reasonably modern one from a mondeo or similar, I did this because it gave a big increase in current at low rpm, albeit at the expense of some fan belt wear! I paid 20 quid from a car breaker, had to modify the bracket slightly to align the pulleys. I was more interested in charging two batteries at say 10A each, plus running fridge etc at tickover, rather than some theoretical current at 4000rpm.
The recommendations about smart chargers etc are good, but I think your system is broken, as opposed to not being optimum?
Hope that is helpful.
 
I recently replaced the alternator on the T90 Thorneycroft BMC after a trip to Northern Ireland, during which I discovered any charge in the batteries was down to the solar panels.
The replacement was bought off t'web using the specs in the manual... but unbeknown to me the "standard" 36 amp AMC alternator had been swapped for an isolated earth model, which meant the wiring needed redoing.
The 70amp replacement cost around £60 and the advice from the seller was invaluable. PM me if you want a contact number.
Next job will be to fit a voltage sensing relay which will charge the domestic battery/ies only when the crank battery is up to par.
 
I had very similar sounding problems in the first year I owned 'Fairweather'........Inconsistent charging moving on to no charging at all.

Turned out to be a loose connection on the back of the Ammeter. This manifested its self when the ammeter melted one day as I was mooring at Weymouth !

Certainly I wouldn't do anything a regards upgrading your existing alternators until I had had the existing one checked..these things are pretty robust these days...think of what yr car one puts up with!

Whilst my set tup was giving me problems I never left home with out my trusty 'starter pack'...one of those things from Halfords that looks like a handbag....it would start my Perkins from cold anytime!

Regds Nick
 
similarly to above posts.... get the alternator checked out....

I had similar symptoms, and the alternator checked out fine....

What actually was the cause?.... I had a battery sensed charging set up, to two batteries via a split diode..... in the sensing wire to the engine battery, a small diode had been placed to drop 0.7V to compensate for the diode splitter voltage drop, and this diode had failed..... problem sorted by spending 7p at Maplins!!!!!!!
 
Well i just bought a new Lucas alternator so see if that works! Also what is the point of having the isolation switch?....cars don't have them!
 
[ QUOTE ]
X split module.

If that's what I think it is it is a diode bridge ........... it will reduce the voltage somewhat at the battery itself which can be overcome by fitting a smart charger sensed at the battery or the output terminal of the splitter.

[/ QUOTE ]

You are not quite right about the X-split. It is not a simple diode splitter. It is better to regard it as an electronic version of a voltage sensitive relay (VSR). It does not suffer from the large volts drop that bedevils a diode splitter but at the same time being a solid state electronic device it does not have the moving mechanical parts that a conventional VSR does.

Battery sensing is therefore not necessary. It does not of cousre offer the benefits of a "smart charge" alternator regulator.

I suggest a quick look at the website fot X-alt, x-split etc sometime.
 
Yes I wasn't sure, but my point, that you have re-inforced I think, is that it is not a smart regulator and he would be better to spend his money on a SR rather than a honking big alternator without one. I am sure you agree?
 
Take the alternator off and take it to an auto electrician - you know the sort of place in the grimy end of an industrial estate or under some railway arches. they will check it out and replace parts very cheaply. Mine stopped working last year and was mended for £30 or so. The only reason I knew it wasn't working was because the permanent voltmeter wasn't showing 14+v with the engine on - so I now keep a keen eye on the volts going into the batteries - well worth having that bit of kit !
 
I will get it looked at and keep it as a spare, have now got the new one. Just a thought, i started the engine without the domestic switch on but by accident turned off the eng. start too so might have blown the diode?
 
[ QUOTE ]
so might have blown the diode?

[/ QUOTE ] If I understand you correctly yes you have done what may well have blown the diodes.
 
Please explain the problem caused by battery sensing only sensing one battery bank.

Please also explain why an additional diode fitted to a machine sensed alternator to make it generate the extra voltage to compensate for what is lost lost through the diode splitter will result in the the batteries being overcharged and the alternator being burn out.
 
[ QUOTE ]
Next job will be to fit a voltage sensing relay which will charge the domestic battery/ies only when the crank battery is up to par.


[/ QUOTE ] Uhh- I am not sure that is what will happen - or at least it will be an interesting wiring version with a special VSR.

Normally the VSR detects when the alternator is charging and connects the output to the domestic battery AS WELL as the engine start. The engine start battery is always connected and normal engine starts take very little in the way of Amp Hours out so regain their charge evry quickly. The VSR means that you always charge your domestic bank when the alternator is running. The batteries will sort themselves out and accept appropriate charge according to need, so long as there is enough voltage (with enough amps behind it) available.
 
[ QUOTE ]
split charge diodes are rubbish due to the diode you have a voltage drop which the alternator cannot detect,, <span style="color:blue"> depends on the alternator, how you wire it, and what alternator charge regulator you are using </span> the alternator is only designed to sense one bank of batterys and using another diode to make it sense to is a sure fire sign that you will over charge all your batterys and burning your alternator out <span style="color:blue"> Well it sort of might be true sometimes, but with respect this is just drivel, and sounds like the sort of thing as disreputable marine electrician might say to a customer who knows nothing or very little about boat electrics </span> ,,, phone andy carter 07930330677 he will give you details of a decent setup using a voltage sensing relay <span style="color:blue"> I notice from your profile that you are one and the same person, you ought to have noticed that forum rules forbid you from self advertising. Also there is more than one way to have a 'decent setup'</span>

[/ QUOTE ]
 
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