Lotus Elan

Dynamo Diagnostics

PostPost by: Chrisrich » Sat May 01, 2010 12:44 pm

Trying to troubleshoot a charging problem on an S4, negative ground/dynamo car.
Battery seems to not be getting a charge. I am sorting the car from scratch, and I suspect it never charged properly under my ownership.

I ran the battery down entirely on a drive. When I put a voltmeter at the battery terminals, I see no V increase w/ motor running at any speed.

Have checked the generator as per manual -- bridge across generator terminals and get solid 12v output with increase in engine speed, output in the 20V+ range.

-manual describes a test I simply do not understand:
-pull connectors from gen, link the 2 terminals together
-Start engine
-check V at terminal 'D' on reg. Should see an increase in voltage with engine speed.

If the generator is disconnected and out of the loop, how does this test work? In fact, when I do this, I see about 6v at terminal D, with no change with engine speed. Am I missing something here?

It seems the generator is doing what it should, and I should be looking at the regulator box, which is a bit of a mystery to me. Also, is it correct for me to be seeing continuity between the field and dynamo terminals on the regulator? I have the same condition on my sprite.

Thanks for any advice-

chris
1970 Elan S4 DHC 45/9780 1972 Triumph TR6
1958 Bugeye Sprite 1967 Triumph Trophy 650
1991 Ducati 900ss 1989 Honda GB500
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PostPost by: neilsjuke » Sat May 01, 2010 1:07 pm

Pull the wires of the dynamo link the large D to small F and then run with a voltmeter on the linked terminals and earth the voltage will rise with a rev of the engine but note you should do this for as little time as possible you are looking for above 15v ,As the output is unregulated this would cause the armature to burn out throwing the solder out.
Now you have your head round that I would pull the wires of the regulator D and F and link at that end saves getting near the exhaust and tests the wiring to the dynamo.
Neil
Ps my reply to postings tend to follow how I would test a car in real life so tell me the results and we should get there in the end
Last edited by neilsjuke on Sat May 01, 2010 5:35 pm, edited 1 time in total.
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PostPost by: m750rider » Sat May 01, 2010 5:01 pm

My simple test for the generator is to check voltage at the battery with the engine revved up slightly - should be 13.5+ volts. I have not had a regulator go bad on me in 38 years of owning my S4, but I have rebuilt the generator about 4 or 5 times. My guess is you need a rebuild, any old time shop can do it for you, around here about $100, not too much different than a new one from Dave Bean.

The generators are susceptible to damage from oil, any leaks that blow back from the fan, from around the dipstick especially, will foul them and eventually they go bad.
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PostPost by: cbguerrajr » Sun May 02, 2010 2:57 pm

My experience was the opposite, had lots of trouble with voltage regulator(s). I assume that due to its location in my S2 rain water ran down over it and corroded the contact points. The generator/dynamo never failed completely, but the charging was the usual, anemic.
Chris, if you already have neg ground, fitting an alternator is easy and will result in plenty of charge and no need to test or replace the voltage regulator.
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PostPost by: billwill » Sun May 02, 2010 9:53 pm

Unless you really want to maintain originality, ditch the dynamo & fit an alternator kit.


They really really are soooooo much better.

I lost count of the number of times I had to have a push start while I had a dynamo (first 10-12 years), but I don't think there have been ANY times when I needed a push start since changing to an alternator c 1983.
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PostPost by: Chrisrich » Sun May 02, 2010 10:38 pm

Done.
A new alternator, it is, then.

Thanks folks

chris
1970 Elan S4 DHC 45/9780 1972 Triumph TR6
1958 Bugeye Sprite 1967 Triumph Trophy 650
1991 Ducati 900ss 1989 Honda GB500
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PostPost by: billwill » Mon May 03, 2010 2:03 pm

Chrisrich wrote:Done.
A new alternator, it is, then.

Thanks folks

chris



It does involve some wiring changes & I regret I do not know exactly what they are as my changeover was done for me way back by Vegantune of Spalding.

I think it also needs a new stronger bracket for the bottom of the alternator. It has a sliding fit at one end.

That's why I mentioned a kit, though I don't know if you can get a kit of all the bits in one go, nowadays.

Try Burton or QED.

==============
Very little goes wrong with alternators, they either work or they don't, the bit that fails if anything is the diode pack inside & then you just go get an exchange alternator and you are back to 'as new'.
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PostPost by: collins_dan » Mon May 03, 2010 2:13 pm

I just changed mine over last fall. Ray at RD Enterprises has an alternator and mount that fits perfectly. I had some trouble with the top mounting arm hitting my dipstick, so found a very simple substitute off an old volvo and it works great. I also eliminated the old voltage regulator and changed to a terminal block, which is just a bit neater. Dan
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PostPost by: billwill » Mon May 03, 2010 2:17 pm

Yes you must remove the old dynamo regulator as part of the wiring changes.
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PostPost by: neilsjuke » Mon May 03, 2010 3:06 pm

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PostPost by: billwill » Tue May 04, 2010 1:11 am

Would it not be wise to put a fuse in the feed from the alternator to the battery take off point on the starter solenoid.
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PostPost by: neilsjuke » Tue May 04, 2010 8:22 am

No fuse this would be due to the variable amperage faults you would be trying to cover any fuse should be on the load side.
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PostPost by: prloz » Tue May 04, 2010 11:07 am

Hi Bill,
You are correct. There should be a fusible link between alternator output and battery to limit current flow if the rectifier stack in the alternator short circuits. All modern cars have one. Probably the reason why more than one Elan has burnt to the ground.
Regards,
Peter.
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PostPost by: 69S4 » Tue May 04, 2010 1:12 pm

prloz wrote:Hi Bill,
You are correct. There should be a fusible link between alternator output and battery to limit current flow if the rectifier stack in the alternator short circuits. All modern cars have one. Probably the reason why more than one Elan has burnt to the ground.
Regards,
Peter.


Having just converted my S4 to an alternator last year after years of marginal charging I'm amazed at the difference it made. Absolutely no charging problems since. The wiring changes were easy to do after a few minutes thought and I've left the control box and old wiring in place (just taped up) if I ever get a desire to convert it back.

I managed to modify the dynamo mounting bracket to take the alternator by welding in a few brackets / drilling a couple of holes and a few thousand miles later its been fine. Five minutes with a hacksaw would convert it back to dynamo spec.

I didn't add a fuse in the main feed from the alternator to the solenoid and now realise the error of my ways. I really need to do that. Anyone got any suggestions as to a suitable item / supplier. Be nice if it looked kind of period.
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PostPost by: billwill » Tue May 04, 2010 6:17 pm

Having said all that, I'm not sure if I have a fuse there. I must check. :shock:

I guess it can be quite a big one say 10% over the rating of the alternator. As mentioned its purpose is to stop an extremely high current flowing from the battery into a failed alternator, which would cook the alternator coils and probably start a fire.

As to a mount, I dunno, I would be inclined to find one in a breakers yard? and maybe put a replacement long one replacing the existing one covering the spaces occupied by the existing 4-fuse block and the redundant dynamo regulator.


If you want to look trad, I suppose you could remove the innards of the dynamo regulatorr & mount a suitable fuse block inside the old case.


===============
Thinking back to the Ford Fiesta XR2 that I owned for a while, I seem to remember that it didn't have an obvious fuse there at all, instead part of the actual wiring between alternator & battery was designed to melt away completely. I suppose the idea was that if there was fire in the engine compartment that would also melt the link and cut off the battery.
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