Alternator Issue

Asterix

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Having had my leisure batteries changed to 24v I'm finding my alternator is struggling to get power in them so I'm looking to upgrade my alternator but I'm unsure what affect (if any) this could have on the trucks electrical system.
I've not checked what the power output currently is as the weather has been too dire to lift the cab but I have looked online at possible replacements,one is 55 amp which is what I imagine the one installed is,or I could get an 80 amp one but not sure if this would create other problems. I also wondered if my alternator just needs some TLC?
I was thinking of getting an auto elec to have a look but I prefer to approach any tradesman pre armed with some knowledge so I can ask the right questions or know if they're trying to pull a fast one to make some extra cash.
Any info appreciated.
Dave
 
If over 100 thu miles i would replace with much bigger,the alt is self ajusting to load so 80 to 120ah i would be looking for,which is common these days,my car has a 80ah.
 
Asterix said:
Having had my leisure batteries changed to 24v I'm finding my alternator is struggling to get power in them so I'm looking to upgrade my alternator but I'm unsure what affect (if any) this could have on the trucks electrical system.
I've not checked what the power output currently is as the weather has been too dire to lift the cab but I have looked online at possible replacements,one is 55 amp which is what I imagine the one installed is,or I could get an 80 amp one but not sure if this would create other problems. I also wondered if my alternator just needs some TLC?
I was thinking of getting an auto elec to have a look but I prefer to approach any tradesman pre armed with some knowledge so I can ask the right questions or know if they're trying to pull a fast one to make some extra cash.
Any info appreciated.
Dave
Click to expand...

I suppose I would start by establishing what alternator is fitted and what condition it is in ?
Alternators used to be easy to service by obtaining spare parts from an auto-electrician, but I don't know what the situation is today.
It would be easy to access It's condition by turning everything on and watching the voltage with a multimeter and if possible a clip on ammeter would help check its output.
 
You can buy new brushes,but most the comutator is worn so not worth the bother,best way to test is switch on h lights and rev engine from idle,they should brighten slightly,if they flicker the rectifier is stuffed,if the lights dont come up a bit then brushes as a rule.
 
harrow said:
I suppose I would start by establishing what alternator is fitted and what condition it is in ?
Alternators used to be easy to service by obtaining spare parts from an auto-electrician, but I don't know what the situation is today.
It would be easy to access It's condition by turning everything on and watching the voltage with a multimeter and if possible a clip on ammeter would help check its output.
Click to expand...

I recall fitting new brushes to a car alt when I was young but that was because it wasn't putting out enough for the starter batt. and had put a warning on the dashboard,in this instance it's probably pushing out enough to maintain the starter batts but not enough for the leisure ones.
Is there any sort of formula to work out what amperage would be required to service both banks of 24v batteries?
 
Alternators are pretty reliable - the principal test is to check the output voltage with engine at fast idle.
On a 24v system it should be c28v - anything less and replacement should be considered.
Whilst the rates current looks small compared to car outputs the double voltage means twice the power.
With two sets of batteries to charge the higher output option would make sense if you do need a new one.
 
Asterix said:
Is there any sort of formula to work out what amperage would be required to service both banks of 24v batteries?
Click to expand...
No because it depends how much the batteries are discharged.
That's why I suggest turning every thing electrical on and see how it copes with the power drain. :)
Years ago we had load frames to put on the batteries to see how the battery coped, so by turning on everything see how it manages.
 
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People forget that it may take a run of 40/60 miles to recharge a low battery,but if you have extra ones to charge this will split the charge power ,so it may take a long time,so do fit a much larger alt to cope. (y)
 
Just remember in winter with lights etc the alt will just about cope charging one battery,add a few more and it will have little chance if a standard unit,thats why most campers have a uprated one.
 
Thanks guys that's cleared it up for me,I'll have a look as soon as the weather settles down and see what the alt is actually outputting and go from there.
 
Nabsim said:
Just throwing this in there, is it worth looking at a B2B for charging your leisure battery’s?
Click to expand...

Electrics and me don't see eye to eye but this thread explains my new setup far better than I ever could...

Converting 12V Leisure Electrics to 24V

I mentioned I would be adapting a vehicles lesiure electrics from 12V to 24V .... Well today was the Day :) The van in question was a 7.5t Horsebox on a 4,5l Mann Chassis and owned by Asterix from the Motorhomer.com Forum. The following is what was done, the pros and cons of 12V vs 24V and the...
www.motorhomebuilder.com www.motorhomebuilder.com
 
I'm not that enthusiastic about B2B preferring a simple alternator triggered relays and good sized cables direct to the leisure batteries.
Which is often a much cheaper solution.
A good auto-electrical will check the voltage at the leisure batteries when then are charging - if it's not within 0.1-0.2v of the alternator output then the cables need upgrading.
A parallel feed can be provided rather than replacing existing - this reduces cable size needed.
 
Markd said:
I'm not that enthusiastic about B2B preferring a simple alternator triggered relays and good sized cables direct to the leisure batteries.
Which is often a much cheaper solution.
A good auto-electrical will check the voltage at the leisure batteries when then are charging - if it's not within 0.1-0.2v of the alternator output then the cables need upgrading.
A parallel feed can be provided rather than replacing existing - this reduces cable size needed.
Click to expand...
Known as KIS ,keep it simple.
Never put all your apples in the one barrel.
Keep units sep as if not one down all down.
 
Having just fitted a BMV to my 811D merc, I notice on start up about 30 amps going into the batteries at ide. It soon drops of as the engines batteries are normally well charged whilst parked up. The alternator I think only 55amps at 24 volts. I can't imagine needing more.
 
Asterix said:
Electrics and me don't see eye to eye but this thread explains my new setup far better than I ever could...

Converting 12V Leisure Electrics to 24V

I mentioned I would be adapting a vehicles lesiure electrics from 12V to 24V .... Well today was the Day :) The van in question was a 7.5t Horsebox on a 4,5l Mann Chassis and owned by Asterix from the Motorhomer.com Forum. The following is what was done, the pros and cons of 12V vs 24V and the...
www.motorhomebuilder.com www.motorhomebuilder.com
Click to expand...
I notice on that thread it says @24v battery’s will not fully charge, needed heavier cables. Did you have those fitted?

it’s above me this one, have you asked Dave?
 
Nabsim said:
I notice on that thread it says @24v battery’s will not fully charge, needed heavier cables. Did you have those fitted?

it’s above me this one, have you asked Dave?
Click to expand...

He thought he was going to need heavier cabling but the existing cable was more than enough,I did talk to him about my alt charging but vehicle electronics isn't really his thing.
 
Alternators break on motorhomes all the time as they're never uprated yet are asked to perform differently. Buy a bigger one, the prices don't differ much. My old alternator was 50A and if I had my fridge on 12v the b2b charger would keep cutting out if the engine revs dropped below something like 2000rpm, upgraded to a 70A and it stopped this.
 
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