Alternator Charging worries !

[Marcsnapon]

I'm slightly concerned that my T25 (1985 petrol) may not be charging correctly ?
I use my van daily for work and whilst it never fails to start the volt meter fitted rarely goes over 12.5 volts.
With lights, heater etc on the voltage holds at about 12.5 volts, am I correct in thinking that after starting up I should see over 14 volts or more which then falls as the battery is charged ?
The battery is fairly new, alternator belt new and connections appear good.
Am I worried over nothing ?

[Sir Brixalot]

I had a lot of problems, for me it turned out that the brushes had worn, main battery wire was virtually severed under the heat shrink although it looked OK superficially, the blue wire from the ignition was very worn and the gearbox earth strap underneath was pretty corroded. Oh and the battery was weak so I'm amazed it started at all! I get 13.6 now when driving. The mods will probably move this post into technical where you'll get the experts helping.

[itchyfeet]

Alternator charges at around 13 to 13.5 volts, some regulators get close to 14V
12.5 V is too low, your voltmeter may be inaccurate and it matters where it's connected, try measuring volts with a multimeter at the alternator when running and measure your batt at the terminals after leaving over night to rest (measuring after charge or use gives inaccurate measurement)

You may have something like a stereo draining the batt daily, you need to drive your van for some time daily in winter to replenish the loss, lots of short journeys mean your batt will be low and alternator needs to work hard to charge, this can mean voltage measurements are low if they are not measured at the alternator.

[Marcsnapon]

Good advice chaps, I will check things out at the weekend.
Regards Marc

[itchyfeet]

check your battery connections, batt to body earth strap, gearbox to body earth strap, starter motor to alt 12v lead connection, all these can make a difference of 1V.

remove, clean, vaseline, replace.

[ghost123uk]

your voltmeter may be inaccurate

May I bang on again about those cheap Volt meters that can be miles out

and it matters where it's connected

Too true. I have a multi function do dah on top of my dash and the Volt meter part of it is not only inaccurate, but as it takes it's feed from a live wire from the fuse box, it ain't really reading battery voltage, things like the ignition circuit, the lights, heater blower, wipers etc all drag the voltage at that point down quite a bit.

Try measuring volts with a multimeter at the alternator when running

And perhaps at the battery too. You should see more than 13.5 Volts at the battery (engine running), but measure it after a bit of a drive. If it's less than that, consider getting a replacement brush pack for your alternator. You can get them up to 14.5 Volts these days (and that is the one to go for). Get a decent make like Beru. Cost about £15 and take 15 minutes to fit, max.

All this is assuming you own a half decent multimeter of course

[California Dreamin]

Alternator charges at around 13 to 13.5 volts, some regulators get close to 14V
12.5 V is too low

Original 'Volkswagen checking tolerance' was 13.9 - 14.2 volts .....check at the B+ post on the alternator (13mm nut). Slightly more difficult on early alternators where you need to get into the black push on connector. Checking at the alternator will give you the 'actual' output voltage, if you then check at the battery you can see any 'loss' (voltage drop) in the wiring.

New brush packs/voltage regulators, tend to be set to give a slightly higher output better suited to the newer battery chemistry's introduced since the 90's.

I would just take the engine off idle (1500 - 2000 RPM something like that) whilst checking.
You need to be seeing over 13.9 volts at the alternator.....and IMO at least 13.7 volts at the battery but that would be an absolute minimum.

Just be aware that low readings can often be attributed to additional 'leisure' battery 'faults' pulling down these figures so I would advise that you disconnect any 'extra' batteries in the charge circuit whilst carrying out these checks.

Martin

[willpom]

Hi,

I've been having problems with my starter battery recently and am trying to figure out why. Just replaced it as it now reads 0.4V across the terminals.

My set up

• Standard 440Ah battery
  Leisure battery
  Split charger for alternator charging
  
  100W solar panel
  Duo battery charger with output screen
  I added this to give us a bit of time with today's gadgets when off grid staying put camping so not having to need to fire up the engine. It also acts as a trickle charger as I fitted an alarm with immobiliser, motion & door sensors; this draws about 200mA and runs off the starter battery.

Firstly I'm investigating whether the panel has died as I get no short circuit amperage across it when 1.5 months ago I did even on an overcast day.
Secondly I replaced the starter battery as even after a 250 mile round trip it didn't hold it's charge for more than 24hrs.
Thirdly the leisure battery seems fine - been jumping the van off that for past month.

In trying to determine the problem I've measured the voltage across the battery with the van running; 13.6-13.7V, this is about the same with and without the leisure battery connected up. So Martin from what you are saying my alternator is probably borderline.

You need to be seeing over 13.9 volts at the alternator.....and IMO at least 13.7 volts at the battery but that would be an absolute minimum.

Ghost, you make this sound easy, even with my output being borderline it makes sense to upgrade the bushes to be on the safe side, do you have a link to one of these quality kits? Is it a soldering job?

consider getting a replacement brush pack for your alternator. You can get them up to 14.5 Volts these days (and that is the one to go for). Get a decent make like Beru. Cost about £15 and take 15 minutes to fit, max.

Thanks, Will

[Oldiebut goodie]

Firstly I'm investigating whether the panel has died as I get no short circuit amperage across it when 1.5 months ago I did even on an overcast day.

If you shorted the output there is a very good chance that you have fried the panel! You can only test voltage across the terminals not current!

[willpom]

If you shorted the output there is a very good chance that you have fried the panel! You can only test voltage across the terminals not current!

Voltage, I meant open circuit voltage, across the panel

I tested for shorts in wiring between panels and controller using continuity.

[ghost123uk]

Hi, you really should start your own thread you know. The replies get confusing when 2 folk are talking about similar things on one thread

Just replaced it as it now reads 0.4V across the terminals.

Please explain what you meant there.
Oh, and 13.7V at the battery is ok and is pretty much "factory spec". A new regulator / brush pack rated at 14.5V will likely give you ~14.2 at the battery end, which is better for faster charging of both batteries.

Talking of the regulator / brush pack assembly.

Ghost, you make this sound easy

It is easy, very easy, 2 screws and a wiggle and the old one is out, a bit of (careful) jiggling and the new one is in, put back the 2 screws = job done.
Available from any motor factors, Brickwerks HERE, or Ebay.

[CovKid]

You do have to remove fan belt and swing alternator to the right though otherwise one of the screws that hold regulator in place is a challenge to get at. I know, because I upgraded my reg pack to a 14.5v one last week.

[ghost123uk]

^^^ well yes, if you want to make life easy for yourself, you could do that

[CovKid]

Getting a good charging voltage at batteries is I think, a combination of minimising voltage drop (ideally with new, fat main cables) and a good regulator. On the stock OEM regulator (14v) I got 13.7v at starter battery using a digital meter. With a 14.5v regulator, I now get 14.07v at starter battery. Difference is sleight but certainly better to have the charging voltage in the upper realms than barely scraping the minimum. particularly if you're running with upgraded headlights and all the other additions we have now. I don't advocate 'adjustable' regulators as I'm sure theres something more intelligent out there that does a much better job of managing charging voltage/current.

A fairly stock T25 with original main cables, will after 30 years be in need of refurbishment/replacement with frayed/corroded cables fairly common once you start digging.

[willpom]

It is easy, very easy, 2 screws and a wiggle and the old one is out, a bit of (careful) jiggling and the new one is in, put back the 2 screws = job done.

You do have to remove fan belt and swing alternator to the right though otherwise one of the screws that hold regulator in place is a challenge to get at. I know, because I upgraded my reg pack to a 14.5v one last week.

Cheers guys. I think the extra ooomph will help the battery with it just being used for short local trips most of the winter. Will look at the wiring at a later date

Sorry about the thread divergence, wasn't really seeking any info on that, just explaining my setup and the known prob I had.