Lotus Elan and Lotus Elan Plus 2 Forums

Dear All

Back from two weeks in Corfu and ready to go........before I went my battery failed (I think-still have to test it) but while I was on the sun lounger a thought came into my head,I am sure I read somewhere that Uncle Colin increased the diameter of the alternator pulley so as to slow it down and compensate for the high revving nature of the engine......now I'm no racer and do take it up to 5500 at times,but,living in a traffic jam U.K. I tend to toddle around at around 3000-3500 rpm (fifth gear,70mph,legal limit Mr Plodd Sir),so the question is this....should I find a smaller pulley to increase the alternator revs/output and maybe better charge my new battery?

John

john.p.clegg wrote:I am sure I read somewhere that Uncle Colin increased the diameter of the alternator pulley so as to slow it down and compensate for the high revving nature of the engine......John

John, I could be wrong but I've never heard that but the T.C. crank pully is smaller than a Cortina one but I think it is more to do with slowing down the water pump than changing the generator/alternator speed, one of the alternators main plus factors is that it charges at at a slow speed as opposed to a generator.

I had problems in maintaining a good state of charge in my alternator equipped +2. I ended up replacing the alternator pulley (appox 80 mm diameter) with a smaller diameter pulley (approx 60 mm). I suspect that first pulley was in fact the old generator pulley that was not replaced when the car had an alternator fitted.

It now hold the charge much better and I rareley have problem with my batteries state of charge.

All the best
Andy

andyhodg wrote: I ended up replacing the alternator pulley (appox 80 mm diameter) with a smaller diameter pulley (approx 60 mm). I suspect that first pulley was in fact the old generator pulley that was not replaced when the car had an alternator fitted.

Andy

Just quickly measured the old dynamo and new alternator pulleys and they measure 78mm (dynamo) and 62mm (alternator). The alternator one has a sort of fan arrangement on it to pull air through the unit which the dyno pulley doesn't have. Starting the car, particularly when hot, was always a problem with the dynamo. Changing to an alternator and replacing the battery has sorted it. My wife has even agreed to go in it again recently, confident that she won't have to push at some stage


Stuart

Thanks both

When you give the diameters ,is that at the bottom of the V or elsewhere?

Thanks

John

Technically, to calculate the speed ratio, you must use the pitch diameter of the drive and driven pulleys. If it's just to get a rough comparison to know which is on the car, the O.D. will probably do.

The sizes I quoted were the OD's and approximate. I actually found an alloy old v-belt pulley in my garage which appeared to be about right and machined it to fit at home. (removed the boss, bored for the correct shaft diameter and cut the keyway.)
Andy

Hi John

Not sure if this is a serious question or not.

If your alternator is spinning fast enough to charge the battery when the engine is at idle , ie it's output is around 14 volts, then I can't see how spinning if faster will make any difference at all. The control circuit should be regulating the output voltage irrespective of what the engine speed is doing. In any case, more voltage dosen't mean better charging, it will just boil up the battery.

I suggest what you need is to buy a new battery

Regards Andy

I don't think you necessarily expect the alternator to reach the target charging voltage (14-15v) at idle anyway. I've not measured it on the twink but You normally have to rev the engine a little, say to 1500-2000 rpm, before the charging voltage is achieved, At higher revs, the alternator regulator should be limiting the charging voltage - if the voltage keeps going up then the battery will be overcharged and will be fried, and you need to replace the alternator regulator urgently.

If your battery is new, and you measure 14-15v at the terminals when at fast idle and above, then I don't think there is any merit in changing anything. If you are having problems (ie the battery keeps going flat) then you'll need to start looking for another problem (eg alternator brushes, or wiring elsewhere, or some circuit permanently on drawing current somewhere).

Paddy

All

The problem started at Newark,something like 70 miles away,after a "spirited" drive there and a look around the autojumble for about 4 hours the battery would not spin the engine enough for it to catch....a jump start fixed it.....so either something was draining the battery,the battery wasn't charging or the battery wasn't holding its charge.....

Sad to say I bought another and left it to trickle charge for two weeks (Corfu)....the old battery measured 13.5 volts and dropped to 10v while cranking (fast enough for me),so replaced with the new one....similar readings....so now have both batteries in the boot coupled together with a diode,so hopefully both will be charging and if the main battery goes flat I'll have another charged battery to jump start myself with....or so the theory goes....

John

You need to check the voltage and the amps as alts may show correct Voltage but only half the current with some faults. And check for current drain when parked up. (alarms / clocks will drain the battary.
Neil

This was a potential problem with dynamo charging when doing lots of low rev's traffic motoring.

Shouldn't be an issue with an alternator .......the battery is a duffer

It may be the alternator beginning to fail. If you can find a (competent!) auto electrical specialist and ask them to bench test it (only takes minute) you can tell one way or another. I had six months of a gradual deterioration in apparent battery performance before I got the alternator checked out - ?35 for a new alternator sorted out the problem. The Auto electrician supplied a non standard unit (Maestro I think), with higher output and swapped over the pulleys to get the correct offset. The bench test consisted of spinning the unit on a bench rig & testing output at various revs. Still using the same battery....

Jeremy

i too had a bit of a problem and boiled the battery,i replaced the alternator and got a new battery.not had any problems since. i also took my origonal battery to a shop and it was drained and filled with fresh acid and disstiled water.after a week of tricle charging with a halfords charger i have the battery back working again.
my thoughts are that the alternator caused the damage, as has allready been said,a modern alternator will provide enough charge from just of idle and will regulate its self as the revs rise.if the diode pack is not working then it will over charge and cook your battery leading to a possible miss diagnosis of the origonal fault.

a good idea may be to get a solar charge unit that plugs into the lighter socket,or straight to the terminals.