Alternator woes....

[Stimpy]

A quick question for those who are into electronics or hi-end car hifi nuts

I seem to have problems with alternators, batteries - ANYTHING electrical.


My issue is that I have a complex car Hifi system with an active bass


When the car tick’s over nicely at 500 rpm it’s not enough to keep my alternator running at 12 to 14.2 volts
When the fan cuts in it just adds to the problem


So - when I stop at the traffic lights - and I’m enjoying the sound of my system - the whole thing starts clipping, rebooting, blanking out etc as its getting less than 12 V


It’s meant to be an uprated alternator (fitted) but it just doesn’t deliver the goods at low revs.


I could set the tick over to 1000 rpm but every instinct tells me that’s not the way to sort it.


Do you have any recommendations on a good replacement alternator? I notice that some HiFi -loving people ‘in the know’ fit diesel car alternators that just happen to fit the holes right (not on a Stag though)


Cheers
Steve

[stag8manod]

Hi Steve, One option would be to either fit a smaller pulley to the alternator or a larger one to the crankshaft and speed up the alternator so it is running fast enough at engine idle to charge. Not a quick easy fix but do able.
Cheers Ian A

[KOY 23]

Good advice. You should measure your pulley width and diameters and test at what engine speed your hi fi is working well, so that you know the %age increase you need. Contact a good alternator reconditioner with this information and they should be able to help. Remember a smaller pulley will increase the alternator revs at low and high engine revs, so check that it's not being over revving when you are enjoying yourself. Diesels don't rev as high as petrols so alternator can be geared to spin faster at low engine revs, with out over revving it.

[milothedog]

Don't some of these cars with powerful hifi systems have an additional battery connected in parallel.

[Guest]

As above, you could fit a smaller pulley. The Alternator should have a max volts out no matter what the revs? Or as Ian says fit another battery in parallel, maybe in the hood well?

[mole42]

Turn the music down in traffic.

[StagJonno]

If fitting a second battery, then suggest you use a split charging system as usually used on motorhomes. The second battery being dedicated to your sound system.

The split charge system basically gives you 2 x independent batteries, but sharing a common charging system from the alternator. Therefore your sounds battery never sees the load of your lights, fan etc. Never fitted one myself, but expect that complete kits will be available which should be OK for a DIY install, or use an auto electrician. Second battery could possibly fit in a box at the bottom of the hood well or boot.

Jonno

[GDPR]

As above, you could fit a smaller pulley. The Alternator should have a max volts out no matter what the revs? Or as Ian says fit another battery in parallel, maybe in the hood well?

The alternator will have a Vmax of about 12000rpm that for obvious reasons shouldn't be exceeded or there could be physical damage to the rotor or its bearings. That is assumed on a 2:1 pulley ratio and engine Vmax of 6000rpm - a reasonable assumption. Something from distant memory says that Bosch alternators will spin faster - worth checking if that is still a fact and if you can find one to fit the Stag.
Luckily that Vmax is very much higher than the old Dynamo, whose armature would get very hot at high speed and splatter the solder out of the commutator joints

[Motorcycle mad]

Hi
In my view your problems are in the wiring and not the alternator. With the Stag, and a lot of other vehicles from the 1970’s they were made with many wiring connector plugs/sockets in there harness to help with production line assembly, and now 40+ years later we are suffering with voltage drops caused by corrosion on terminals (even battery terminals), poor fuse box connections, or even bad (diy) wiring mods, resulting in charge not getting back to the battery. The original alternator produced 45amps, and that is more than enough to cope with the electric demand of the Stag with all its lights, wipers, ignition, electric windows, etc. with a total consumption of probably 40-43amps, and not all of this equipment is used continuously (i.e. electric windows, heater fan, wipers), and also how much of this time is at night? A simple check to see if you have a voltage drop of any sort, do the wipers go slow, or do the electric windows go up and down slowly, but performance is much improved when the engine is revved up. OK we are now fitting an electric cooling fan so power consumption is increased, and may be a need in this situation for a higher output alternator?
Another concerning issue is, why are there a lot of alternator failing after a relatively short period of service, generally speaking, in there day an alternator would last for many years, but now on this forum I am reading about alternators being replaced after 12 months, and we only do on average may be 2500 miles a year, what’s going wrong, are they being miss diagnosed, did they need replacing in the first instance?
Are we stop/starting our vehicles to much, therefore not putting back into the battery what was being taken out to start the vehicle in the first instance, it was suggested that a vehicle needed to do 10 miles to put back into the battery what was taken out for initial starting.
Back to your situation with regards to tick over, and voltage drop off to below 12v, this is suggesting the battery is not getting the charge from the alternator (voltage drop/ wiring). Alternators were designed to start charging at approximately 1000 alternator rpm, which would be about 500 engine rpm (i.e. 2-1) but output would be about 0-1 amp at that speed, for these short periods the battery should keep your bits and pieces alive if the battery was fully charged.
These are just my thoughts on this situation.
Ken

[StagJonno]

Ken, I agree that high resistance connections may be part of the problem, but don't underestimate the demand of the electric fans that many of us have fitted. My Kenlowe is taking 18A on normal, 24A on boost. Lights on dip take ~11A (with full beam ~21A); Ignition & radio say 5 - 10A, so it's not too difficult to exceed the rating of the alternator, before possibly using the heated rear windscreen (another ~10A). Also, the charge rate of the alternator is not it's full output at all engine revs above 1,000 - it rises with engine speed up to its rated value, then flattens off. My general observations on mine is that the engine needs to be doing >1500 rpm just to match the demands of the fan on normal setting, ignition & radio and the PO told me he'd fitted an uprated alternator (presumably rated between 60 - 80A).

I've got a current clamp so will have a more detailed look when I get chance.

Jonno

[Stimpy]

As above, you could fit a smaller pulley. The Alternator should have a max volts out no matter what the revs?

This is my thought - it's actually behaving more like a dynamo.
BTW - The stereo is not the sort with external amplifiers and crossovers and that sort of malarky - it has a touch screen though, which needs a bit of juice to work. I have an active subwoofer that sits directly under the driver seat but I've wired a switch to it so I can turn it off if necessary - like in heavy traffic and the fan is on. Totally crap 'solution' but until I get it fully sorted I cant do anything else really.

Ironically my mini DOES have a full blown top end system in it and all works fine on the original battery!

[Stimpy]

The alternator will have a Vmax of about 12000rpm that for obvious reasons shouldn't be exceeded or there could be physical damage to the rotor or its bearings. That is assumed on a 2:1 pulley ratio and engine Vmax of 6000rpm - a reasonable assumption. Something from distant memory says that Bosch alternators will spin faster - worth checking if that is still a fact and if you can find one to fit the Stag.
Luckily that Vmax is very much higher than the old Dynamo, whose armature would get very hot at high speed and splatter the solder out of the commutator joints

Interesting bit about Bosch - going on the lines of paying a bit more but getting a much higher grade re: quality

[Stimpy]

Hi
In my view your problems are in the wiring and not the alternator. With the Stag, and a lot of other vehicles from the 1970’s they were made with many wiring connector plugs/sockets in there harness to help with production line assembly, and now 40+ years later we are suffering with voltage drops caused by corrosion on terminals (even battery terminals), poor fuse box connections, or even bad (diy) wiring mods, resulting in charge not getting back to the battery. The original alternator produced 45amps, and that is more than enough to cope with the electric demand of the Stag with all its lights, wipers, ignition, electric windows, etc. with a total consumption of probably 40-43amps, and not all of this equipment is used continuously (i.e. electric windows, heater fan, wipers), and also how much of this time is at night? A simple check to see if you have a voltage drop of any sort, do the wipers go slow, or do the electric windows go up and down slowly, but performance is much improved when the engine is revved up. OK we are now fitting an electric cooling fan so power consumption is increased, and may be a need in this situation for a higher output alternator?
Another concerning issue is, why are there a lot of alternator failing after a relatively short period of service, generally speaking, in there day an alternator would last for many years, but now on this forum I am reading about alternators being replaced after 12 months, and we only do on average may be 2500 miles a year, what’s going wrong, are they being miss diagnosed, did they need replacing in the first instance?
Are we stop/starting our vehicles to much, therefore not putting back into the battery what was being taken out to start the vehicle in the first instance, it was suggested that a vehicle needed to do 10 miles to put back into the battery what was taken out for initial starting.
Back to your situation with regards to tick over, and voltage drop off to below 12v, this is suggesting the battery is not getting the charge from the alternator (voltage drop/ wiring). Alternators were designed to start charging at approximately 1000 alternator rpm, which would be about 500 engine rpm (i.e. 2-1) but output would be about 0-1 amp at that speed, for these short periods the battery should keep your bits and pieces alive if the battery was fully charged.
These are just my thoughts on this situation.
Ken

Thanks for such a comprehensive post. Very interesting.
I can't remember when/where I bought the alternator but i do know it's 75 amps - which is great when everything is spinning correctly.

[GDPR]

This is my thought - it's actually behaving more like a dynamo.
BTW - The stereo is not the sort with external amplifiers and crossovers and that sort of malarky - it has a touch screen though, which needs a bit of juice to work. I have an active subwoofer that sits directly under the driver seat but I've wired a switch to it so I can turn it off if necessary - like in heavy traffic and the fan is on. Totally crap 'solution' but until I get it fully sorted I cant do anything else really.

Ironically my mini DOES have a full blown top end system in it and all works fine on the original battery!

I don't know if this is relevant to your situation, but I used to have terrible problems with my stereo cutting out at higher volume levels - it is just a "cooking" Sony 4x45w with Bluetooth - I thought it was heat related, being backed right up against the heater box. On first use I could use normally but after about 15 mins I couldn't go above volume 19 or it would die - it was like this for years.

Anyway, I needed extra position 1 power sources for USB chargers etc prior to this years Classic Le Mans so I put a 50 amp fused cable direct from the battery into the cab and used the existing radio feed to switch a relay, creating a new position 1 supply, but as I was already behind the console I connected the stereo to the new switched supply.

What a difference - it will play at full volume all day - it seems there must have been a resistance in the accessory circuit that heated and dropped the volts off causing the problem.

Maybe you should try this before blaming/changing alternators?

just a thought

Russ

[Stimpy]

It's an interesting thought - thinking 'in reverse' - If I remove the stereo unit and drove the car would that be something that can be proved by checking the voltage (at idle and any speed)?

I guess I could 'manually' fix a cable to the batt+ and run it through (carefully) to the stereo as a temporary test.

My money is still on the alternator, though! :-)



A question just bounced into my head.....

Are there any other car manufacturer/make alternators that fit the Stag (e.g. will a Honda Civic alternator sit nicely on the bolt holes of the Stag?
Maybe a DAF lorry or something!!!! :-D