RB 340 Control Box

[alfadave]

On my plus 2 , I have dynamo and RB 340 control box.

With the engine running, I'm only getting 12V at the battery.

The dynamo is giving out 14V, and the wiring to the control box has checked ok.

I have 2 spare control boxes......I've tried both and still only 12V at the battery.

Is there any way of checking/repairing the control box, or is it simply a matter of replacing it?

[Andy8421]

When you say you have 'checked out the wiring', does this mean you have measured the voltage on the 'B' and 'D' terminals on the control box relative to ground when the engine is running (at decent revs, not at tickover)?

If the RB340 and wiring is working OK, you should be getting dynamo output voltage on 'D', and the internal cut-out relay in the RB340 should have closed and connected this to 'B', so dynamo output voltage should be there as well.

Section B5 of the linked Lucas publication describes the RB340:

https://www.lrsoc.com/forum/forum_files/Lucas%20Manual%20B.pdf

Good luck.

[alfadave]

At approx 3000rpm,

at the control box I'm getting 12v at B

and 4V at D

[Craven]

Do you have a flat battery or what, a voltage regulator output is a switched dynamo output so if you have a flat battery then you probably will only read 12volts with a meter. You need to put a bit of insulation in the cutout contacts to read the controled voltage. All in the link that Andy 8421 provided.
FWIW

[Andy8421]

At approx 3000rpm,

at the control box I'm getting 12v at B

and 4V at D

If you really meant 4V at D, and not 14V, then your wiring is adrift. The D connection on the RB340 is supposed to be a direct connection to the output of the dynamo - you mentioned earlier that the dynamo output was 14V?

One thing that often gets missed is that the 'E' connection on the control box needs to be earthed. Given the flaky earths on the Elan generally, if everything else is OK, worth checking that you have a decent earth.

[alfadave]

Yes it was 4V at D

Checked the earth is ok.

The RB 340 was NOS still in a box, but stored for many years.

[gjz30075]

Yes it was 4V at D

Checked the earth is ok.

The RB 340 was NOS still in a box, but stored for many years.

It still needs to be adjusted per Section B5. There might be plastic rivets
holding the case to the base and they will have to be ground off to get
access. Then replace with small bolt and nut.

[Andy8421]

Yes it was 4V at D

Checked the earth is ok.

The RB 340 was NOS still in a box, but stored for many years.

Dave,

If you are getting 14V at the Dynamo output, and 4V at the D terminal on the control box, then you need to find out why. There should be a single run of wire direct from the Dynamo output to the control box D terminal, so perhaps the connectors have corroded, or the wire has broken. Its a pretty hostile environment at the back of the dynamo close to the exhaust, the insulation cooks and cracks, and can allow water to corrode the conductors unseen inside the wire.

A simple test would be to run as separate length of wire from the D terminal to the dynamo output, and see if that cures the problem.

Good luck.

[types26/36]

[quote There might be plastic rivets
holding the case to the base and they will have to be ground off to get
access. Then replace with small bolt and nut.

Usually the plastic rivets can be removed by pushing the centre pin out like these shown in this link.
https://www.amazon.co.uk/Plastic-Rivet- ... 9697&psc=1

[alfadave]

Dynamo output was 14V yesyerday.

Today, its varying wildly from low, up to 19V.

Before settling at 3.6V

It needs attention methinks!

[steve lyle]

Sounds like a good time to switch to an alternator! You can both simplify, and dd lightness. Colin would be proud.

[alfadave]

The dynamo checked out ok at Middletons Lucas Agents in Manchester. Step back in time place, reminiscent of the four candles sketch!

So, I fitted a new RB 340 control box from Holden Vintage and Classic.

Looking at a video on their website, it seems they manufacture and individually test these on site. And they seem very reasonably priced.

Battery now charging properly, I'm glad to say.