over charging

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traumjaeger
Posts: 8
Joined: Mon May 15, 2017 3:04 pm

over charging

#1 Post by traumjaeger » Thu Jul 13, 2017 2:45 pm

Hi all,
My dynamo is over charging and affecting my rev counter. The question is how do I reduce the charge on a Lucas RB 340 Regulator?
My electrical knowledge is not the best so please keep your replies simple for me.
Many thanks
T

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JPB
Posts: 9292
Joined: Fri Jan 07, 2011 3:24 pm

Re: over charging

#2 Post by JPB » Thu Jul 13, 2017 5:21 pm

Does this dynamo drive the tachometer mechanically? If so, then it cannot affect the reading as a result of an overcharging problem, only a mechanical one in the flexible drive or a worn male square at the dashboard end. The generator itself doesn't regulate its output, that's the job of a regulator which is usually found on the engine bay bulkhead or an inner wing, there are several guides on the web to checking and adjusting these, here's what to look for, assuming that your car has a Lucas generator:

Image
John

traumjaeger
Posts: 8
Joined: Mon May 15, 2017 3:04 pm

Re: over charging

#3 Post by traumjaeger » Thu Jul 13, 2017 7:06 pm

Thanks for the reply.
The tacho is not mechanical but electronic. it has been working fine but suddenly refused to go above 750 R.P.M. I contacted the chap who rebuilt it and he told me that the electronics are voltage sensitive and do not like any voltage from the dynamo exceeding 15 volts and checking the output on a fast tickover I am getting 15.73 volts which indicates that I need to back off on the regulator output, hence the question. The regulator that you show is not the correct one which should be a RB 340 type

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JPB
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Re: over charging

#4 Post by JPB » Thu Jul 13, 2017 7:49 pm

What are you reading with a load on the generator and does the tachometer still refuse to respond correctly then? The figure you're finding is certainly within the regulator's range of adjustment if there are no faults, but why would it be out of adjustment without having been set up that way? I would suggest that you go with your own suggestion and try making the adjustment, but before doing that try another meter or better still, the one used by the person who set the regulator up initially, this will at least tell you which component is in need of attention, the tacho or the regulator.

:idea: What type of tachometer is this? Has it been rebuilt using ICs in place of its original, discrete components?
John

suffolkpete
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Joined: Sun Jan 23, 2011 11:54 am

Re: over charging

#5 Post by suffolkpete » Fri Jul 14, 2017 9:22 am

I would advise against fiddling with the regulator unless you know what you are doing. As John says, the figure you are getting is within the range of adjustment and the voltage output should fall well below that when you switch on the lights etc. Dynamos, with their mechanical regulators, are not as well regulated as alternators and you can see a wide range of voltages and while you wouldn't see more than 15 volts with an alternator, it is perfectly possible to see this with a dynamo under light electrical load and a fully charged battery. Try measuring the voltage with the lights on If it is below 15 and the tacho still doesn't work then take it back to the person who rebuilt it. Try running the engine up to say 3000 rpm with the lights off and if the voltage rises significantly then the regulator is faulty and should be changed. A car is quite a hostile environment for electronics and a design that won't work above 15 volts is, in my opinion, not fit for purpose.
1974 Rover 2200 SC
1982 Matra Murena 1.6

rich.
Posts: 6124
Joined: Wed Jan 05, 2011 9:18 pm

Re: over charging

#6 Post by rich. » Sat Jul 22, 2017 9:12 am

i had a small problem with my jcb, when it was running the buzzer was always going off & the only way to shut it up was to put the lights on.. this worked fine for ages until one day the dash started pouring out smoke & the wiring started to melt.. anyone have any idea whats wrong??

alabbasi
Posts: 235
Joined: Wed Jan 12, 2011 9:54 pm

Re: over charging

#7 Post by alabbasi » Sun Jul 23, 2017 1:35 pm

Not read completely through but are you sure that you don't have a bad ground (earth)? Wires can get mighty hot if there not enough ground and tach will act bonkers.

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