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Rick

Not enough electric to drive at night

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Hi Guys,

It's a '82 Turbo (carbs, wet sump).

If I have the dipped beam on and the cooling fans come on, the engines really struggles to keep turning over, from what I assume is a weak spark because of low voltage (just a guess with my limited knowledge of cars and electrics).

It's never cut out of me, but if the cooling fans are on as well as the lights I can rev the engine, but as soon as I bring the clutch up to pull away there is just no power at all and it's extremely difficult to get the car to pull away at all.

It's not to bad if I can keep moving, but as soon as I sit in any traffic it's becomes a problem.

I put a new alternator on when I first got it about 15 months ago. And the battery is 8 months old.

I take it this isn't normal?

Any ideas what the problem might be?

 

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It could be the alternator despite being relatively new, or something as simple as a belt slipping when there's a greater load.  Checking for mechanical problems such as loose pulley (on the alternator), sloppy belt etc would be the first thing to work to rule out.

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try supplementing the earth with a jump lead from battery negative to engine block. - quick to check thats not it!

 

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1 hour ago, Rick said:

I put a new alternator on when I first got it about 15 months ago. And the battery is 8 months old.

Have you checked the alternator voltage output & the battery voltage with a volt meter? They should be over 12 volts with the engine running. 

That should give you an indication. :thumbup:

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1 hour ago, andydclements said:

It could be the alternator despite being relatively new, or something as simple as a belt slipping when there's a greater load.  Checking for mechanical problems such as loose pulley (on the alternator), sloppy belt etc would be the first thing to work to rule out.

I've not checked in the last couple of months TBH, and I guess being a new belt it could have stretched a bit. I'll take another look.

1 hour ago, slewthy said:

try supplementing the earth with a jump lead from battery negative to engine block. - quick to check thats not it!

 

That's a good call, I'll give that a go. There is a half removed alarm in there (by previous owner) which could have some dodgy wiring.

4 minutes ago, jonwat said:

Have you checked the alternator voltage output & the battery voltage with a volt meter? They should be over 12 volts with the engine running. 

That should give you an indication. :thumbup:

Yeah, with engine running about 12, with a few revs 14, and with engine running and lights on it's ok, but not measured with lights and fans on, which I guess would confirm the voltage is dropping too much.

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How have you set the idle?

With older engines that don't have some kind of load compensation (like the Esprit before '89), you should be setting the idle with some electrical loads in place.  On our Bosch '88, I set warm idle to 850 RPM with the interior fan on high, and the headlamps on. With those loads off, my idle is a shade over 1000.

 

That said, the original alternators (you have the 70 amp version?) don't provide very much amperage at idle. This results in the car 'running off the battery' at low engine speeds. Then when the RPMs increase, the alternator must provide extra amperage to replace the power that was lost during the idle period.  This is hard on both the alternator (causes the voltage regulator to 'cook' it's potting compound) and the battery (the compensating charging amperage at higher RPM will tend to 'boil' the electrolyte).

The above scenario is the reason many of us have switched to the Bosch AL49X alternator which provides a LOT more 'juice' at low RPMs.

 

++++++++++

 

PS:  the loose alternator belt is a good possibility.  BTDT.  They can be a PAIN to properly tension. 😣

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Brilliant info.

The idle was set by PNM while they had it in, and then upped a little more because I was having a stalling issue. It does now idle just below 1k with no load, so I'll check that.

TBH it sounds like I want the Bosch AL49X, is it a straight swap?

Yeah, tell me about the belt, it was a massive pain!!!!

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Another check for battery health is to put a multimeter across the poles and watch the voltage with the battery under load. i.e. turn the lights on.

If the battery is ok, it should maintain just under 12 for a decent time.

If it is shagged, you should see the voltage drop away quite quickly.

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The Bosch alternator (used in 80's BMWs) sometimes requires 'clocking'...that is, you remove the case screws and then turn the front VS. back to match the orientation of the OEM Lotus alternator, so that the wiring will reach. It's easy, as long as you are careful to move the pulley side only so that the rear-mounted brushes don't fall out of place.

 

You will also need to acquire a longer lower securing bolt (the one on the tension adjusting strap). Some folks use a carriage bolt with two of the flats ground/filed to fit the slot; I had a welding shop lengthen my OE bolt.

 

More info (with pictures of the swap process) are in several places here and on LotusTalk.com. The All-Knowing Google will find them. :yes:

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BTW I've just re-read the original post.  Your off-idle issue would seem to me, to be a lean running condition. A low idle (in this case due to electrical loads) would make the situation very noticeable!

Just a thought.  :sofa:

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That actually makes a lot of sense, as I think I've not got the fueling quite right on it at the moment. So definitely worth me looking down that avenue, and possibly kill two birds with one stone.

 

Although, I do like the idea of the up rated alt either way.

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Note there were 2 types of alternator used, each have very different different casings, depending on whether the car has A/C or not.

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Ah, yes, mine is the non A/C black top engine.

The alt was the first job I did and my first learning curve into differences between models and years 😂

Yeah, I'll be sure you check I get one that fits, if there is one available for mine.

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