Dynamo Output

testrider

testrider

Active Member
I've had some trouble keeping the battery fully charged in my TC recently. The battery that was in the car when I bought it expired over the summer so I took the one out of the V8 since I'm not using it now and that's just died too. I bought a new battery a few days ago and the car now starts strongly and the charge light goes out straightaway. At fast idle with no load I'm getting 14.5V at the battery, but with lights on full and the heater blower on 2 it only reads 12.4V, dropping to 12.3, 12.2, 12.1 over a few seconds and revving the engine doesn't seem to help.

I don't think that's right, so my question is what voltage should it give on full load at fast idle?

Secondly, assuming it's not right, is it likely to be a control box fault or just worn brushes in the dynamo?
 
Thanks Dave, I remembered that, but I thought yours was overcharging?

The 30amp control boxes only seem to be about £25 on eBay so I might just replace it anyway.
 
testrider said:
Thanks Dave, I remembered that, but I thought yours was overcharging?
Click to expand...

It was Paul, but when it overcharges it kicks out about 18V :shock: 14.5V is about right for a dynamo. I've not had any problems with the replacement control box that I fitted. You'll have seen that on full load my charging circuit was kicking out 13.4V so about a volt more than yours is. The control box should be adjustable but some of them are not. Whip the cover off and have a look. Failing that I'd get another one to eliminate it as the cause.

Dave
 
Thanks Dave I'll give that a go at lunchtime. It's held together with zip ties so I reckon it's given trouble at some point before now.
 
On closer inspection the box lid is riveted on, not sure what all the zip ties were for.

Anyway, I've ordered another one today so we'll see how that goes.
 
New control box now fitted and working. The voltage with minimal load seems to be around 13.5V now and under full load it's about 12.5V as it was before but crucially it's staying at the voltage rather than slowly decreasing and the car will start when I go to drive it next time. I'll remove the dynamo to check the brushes and clean the commutator when I can.
 
Great result. Glad it worked out for you.
Is removing a dynamo on a 4-pot as knuckle-chafingly annoying as it removing an alternator?
So annoying! You can barely get any purchase on the two lower bolts, and it's not like you could remove the whole assembly including mount as one, as the bolt heads are obscured by the sodding alternator! Took me daaaaays to align the alt pulley with water pump and bottom pulley properly!
 
redrover said:
and it's not like you could remove the whole assembly including mount as one, as the bolt heads are obscured by the sodding alternator!
Click to expand...

You need to try again. Taking the alternator off c/w the bracket is the easy way.
 
How do you get to the lower bolts tho? Even removing the top adjuster bracket and swinging the alternator right up, I still can't get to the bolts underneath. Thought I'd tried everything! Might give it another go just to satisfy my curiousity!
 
Great result Paul :D

redrover said:
Is removing a dynamo on a 4-pot as knuckle-chafingly annoying as it removing an alternator?
Click to expand...

The lower bolt is the tricky one. Once you get the dynamo in the right place to tension the belt you lose access to the rear of the bolt unless you have an angled ring spanner.

Dave
 
redrover said:
Great result. Glad it worked out for you.
Is removing a dynamo on a 4-pot as knuckle-chafingly annoying as it removing an alternator?
Click to expand...

I haven't tried getting the dynamo off yet - could be a Friday afternoon job.

Dave3066 said:
Great result Paul :D

redrover said:
Is removing a dynamo on a 4-pot as knuckle-chafingly annoying as it removing an alternator?
Click to expand...

The lower bolt is the tricky one. Once you get the dynamo in the right place to tension the belt you lose access to the rear of the bolt unless you have an angled ring spanner.

Dave
Click to expand...

I have angled ring spanners in various shapes. Maybe I'll take a pic or two during the process.
 
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