Amazon: Testing suspect Dynamo and Control Box on my 131

[fishyboy]

Hi all,
The battery on my 1966 131 is at least 15 years old and I'm off in the morning to Halfords to get a new one (anything above 60 aH and fits should be ok?. This one https://www.halfords.com/motoring/ba...ee-957134.html or this one https://www.halfords.com/motoring/ba...ee-174064.html should both fit ok).

After a couple of weeks standing still the car wouldn't turn over tonight due to a flat/dying battery. Started fine from my jump pack. Ran the car for a good 15mins but only 9.25v at the battery on my voltmeter at idle. AMP light goes out fine.

I suspect there might be a problem with either the dynamo or control box or could it just be down to a knackered battery?

Started to run through the "Dynamo - Testing on the car" section in the Haynes Manual. Connected my voltmeter to terminal "51 B+" and earth and read 9.3 volts. Seems low but Haynes says " the voltage must not be lower than at the battery", which it isn't.

Struggled to understand the next step which involves disconnecting leads from the dynamo. and run to 2000rpm. It doesn't say explicitly but I assume its with the voltmeter still connected to terminal "51 B+". Is this correct?

Does anyone have a idiot proof procedure for checking the dynamo and control box to see if they are functioning properly.

Phil

[swedishandgerman]

Haynes procedure for this is unnecessarily complicated. As far as I'm concerned, the main check you need to do is the voltage at the battery. However, yours is low.

The old charging system needs a good service every now and then and I feel sure many good dynamos have been binned when all they need is this:

• New brushes in the dynamo - these were very widely used and available from most parts stores. Beetle set will do,
• There's a click-clack switch inside the regulator which looks similar to a set of points and, with the battery disconnected - very important - the surfaces need to be cleaned from build up and pitting.

Failure to do the latter can make the step up switch stick resulting in no charge at the battery or worse, it sticks in the charge position resulting in a massive drain when the car's switched off. You can check it's click-clacking by checking the voltage at the battery when switched off (should be more than 12.5V on a good battery) and when running should be at least 13v. Switch off again and it should revert. With the cap of the regulator off - be careful you don't touch it and cause a spark) you can watch the switch flick.

The other thing that frequently causes a battery drain in an Amazon is a build up of corrosion in the fuse box which also benefits from a regular clean up.

If you're getting a battery from Halfords, make sure you ask for a trade discount card. I'm sure they never check you're actually a trade business!

[Ron Kwas]

Phil;

Good info from S&G...to that I might add that with that low voltage (caused by NO, more accurately, LOW, Chg Sys output!...which causes AMP Indicator to stay OFF), it sounds like your Batt hasn't been charged in a while, so it might actually be OK, just at a low State-of-Charge...charge overnight with a mains powered charger, and perform a Load test on Batt (see how much V drops under Starting load) before replacing...if it was me, I'd at least temporarily plug one of those little Cig Lighter Voltmeters in and monitor Sys V under all driving conditions...if it didn't come up over 12.6-13.0V after a long drive or at elevated RPMs, I'd be suspecting Chg Sys! ...9.25V!, for sure! Check height of your Gen's Brushes!

If you are going to clean up VReg/Chg Control contacts, do it this with Batt disconnected (because it is directly connected!), and very gently so as not to affect adjustment. Adjustment of the contacts is not for mere mortals, but should only be undertaken by qualified and experienced individuals using accurate measuring equipment and techniques!

For Charging Sys troubleshooting: https://www.sw-em.com/AMP_Indicator_ON.htm
Generator/Dynamo based Chg Sys info: https://www.sw-em.com/Bosch%20Genera...n%20Detail.htm
Battery Notes: https://www.sw-em.com/Battery%20Notes.htm

The one thing I cannot quite agree with is S&Gs statement of "other thing that frequently causes a battery drain in an Amazon is a build up of corrosion in the fuse box "...I'd like to see a more specific explanation of that.

Good Hunting!

[Derek UK]

9.25v points to the loss of one of the cells. 1/4 of the battery. Even with this battery, if you put your meter across the terminals and rev the engine, and the volts go up to 12v or so, it mans that the dynamo is putting out some sort of charge. If you connect the jump pack your meter might show 12v+ and again should rise when you rev the engine.

Halfords is convenient but expensive. I bought a Silver Exide 069 from Tanya last year. I think it was an 031TE - £70. Next day delivery. Car had a long static run at the end of last year and then in February. Happily started the car after sitting through lock down to a week ago. That's over 5 months. Usual 20 seconds of churning to get the petrol through with the battery showing no sign of reduced power.
https://www.tayna.co.uk/car-batterie...RoCYioQAvD_BwE

[Bob Meadows]

Dynamo:~
Bedtime reading!

[fishyboy]

Hi all,
Thanks for all the replies and reading material.

Removed and cleaned up fuse box. Cleaned all the connections on the solenoid. Installed new battery (12.4 volts on meter). Ran the engine, connected voltmeter directly to battery and and at around 1500 rpm got 13.5volts. So all (in my mind) seems to be working and I'm pointing the finger at a dodgy battery. Time will tell.

Got a 032 Halfords battery for £80 with a 3 year warranty. So much easier taking a dud back to Halfords than trying to return something bought on the internet. For all my other car parts I use my local motor factors where a box of Jubilee clips is about the price of just one in Halfords.

Phil