Funny dynamo problem...

[PulpitNeil]

Hi there,

My dynamo isn't charging. I have tested it by connecting the two terminals with a bit of wire and measuring the voltage between those and the battery. It seems fine, giving up to 18v (with brand new brushes). It gives the same reading at the connection to the control box, and at the control box output. While the two dynamo terminals are connected my ammeter also shows a positive charge, but as soon as I disconnect this temporary link and wire the dynamo up as normal, the amps drop to about -3 and don't budge when I rev the engine.

Now the only thing I can think of is that the dynamo isn't charging because my battery was charged overnight with a charger (while I was waiting for the new brushes to arrive). Does that make sense? What about the amp drain when the engine is running?

-Neil

[Alec]

Hello Neil,

it sounds as if your control box is not working. Nothing to do with your battery being charged. I've done very little with control boxes and that was a very long time ago, so I won't try and avise regarding checks. The simplest is to get an exchange regulator, but do check all connections are sound first.

Alec

[PulpitNeil]

Regulator is brand new, I only swapped it last week. In any case, the voltage from its output is good...

[beero]

I know your regulator is new but are you assuming it is adjusted properly from the factory?
This site will help to diagnose and adjust the regulator
http://home.comcast.net/~rhodes/generator.html

[Alec]

Hello Neil,

"the voltage from its output is good..."

What do you mean by that, if the regulator output was good your dynamo output would be greater than your battery voltage so indicating a charge? When you link the dynamo main and field terminals you are putting a very high field voltage so giving an excessively high dynamo output. The regulator gives a varying field voltage depending on the load and battery state of charge.

Alec

[PulpitNeil]

Sorry, what I meant was that the voltage from control box E terminal to battery earth was the same as the voltage from the linked dynamo terminals to earth. There was no drop, and so I assumed everything in between was in order.

The voltage I'm getting across the dynamo terminals is roughly 18v, same as the E terminal. Battery voltage is 12.8v. You reckon that means there is a charge, but my ammeter isn't budging past the 0 mark, and my headlights aren't getting brighter when I rev.

[bmcecosse]

The output from your Dynamo is good - but the Regulator is obviously NOT working...... Why did you change out the old one anyway? If you still have it - try refitting it!

[bmcecosse]

Crossed posts....... The E terminal should be EARTHED - it should NOT be showing 18 volts.......
And no - 12.8 volts simply shows your battery charger has done a fair job - when the dynamo is charging your ammeter WILL show a charge - and the volts will be 13.4 or so......

[PulpitNeil]

No, I disconnected the E terminal earth wire to connect the meter to it. The 18v was passing through my meter to earth.

[Alec]

Hello Neil,

you don't seem to have grasped that by shorting the main and field terminals together that you are forcing a high dynamo out put, and only proves the dynamo. With the link removed it's not charging so all that's left is the regulator.

Alec

[bmcecosse]

Why on 'earth' would you disconnect the E terminal ??? What was wrong with the old regulator ?

[PulpitNeil]

The old regulator was covered in black soot and letting off little wisps of smoke. I've cleaned it up and popped it back on, and everything's working now!

[bmcecosse]

Be sure to get your money back on the useless one........