Alternator not charging at idle

[F355GTS]

My Duratec has a 40amp Brise alternator with 75mm pulley, at 1,000rpm idle it's not charging although the ignition light goes out.

Metering it last night it needs to be at about 1400rpm before it hits 14v. I think I'm right that I need to fit a smaller pulley to get it to charge at 1,000. 

Can anybody advise what size pulley I need given the centre spindle presumably needs to be spinning 40% faster

 

thanks

[Jonathan Kay]

There are some figures in this thread, including the maximum permissible speed of the alternator. I'd check that end as well as you think about the pulley size.

What voltage do you get at 1,000 rpm?

Has anything changed recently?

Jonathan

[Mark Durrant]

Mark

I would speak with Tim Brise as I always found him to be very helpful. On my R500K I found that once I started the engine I needed to blip the throttle for the alternator to start charging and it would then happily charge at 1,000 rpm. Have you tried this with your alternator?

Mark

[tomwood]

Well I'm glad it's not just me! I too have the same issue on my Duratec car which I assume is the same alternator as yours. So much so that I once got stuck in traffic in the dark and with my headlights on I very quickly ran the battery flat and broke down.

at idle mine is just about OK but as soon as I put something electrical on in the car then I'm on borrowed time. Bit crap really, Caterham should have worked this out for themselves surely.

Tom

[F355GTS]

Tom

Mines not a caterham build and I'm sure woudl be fine with nothing elecrical but in a queue the fan fires up and as with you it drains the battery

Mark

Yes if you blip the throttle it'll charge but as soon as it goes back to idle the charging stops (volts go back to 12.*

Jonathan

12.4 approx at idle, 14.2 if it climbs to 1400rpm. Agree I need to check max revolutions too

 

thanks

[slap_ed]

I think my R400D the same. I just happened to check the voltage at the battery on tickover and I think it read just over 12 volts, as you say not enough to charge the battery. Revving it brings it up to the voltage you'd expect, 14.1v I think. I'll double check this weekend.

[revilla]

Is this not because the R400 and 500 engines have very high rev limits and are therefore fitted with different pulleys to stop the alternators overspeeding at max revs? If so be careful changing the pulleys back again to ones that increase the speed of the alternator at idle as an alternator fan disintegration at full chat will not be pretty.

[F355GTS]

I dont think they'd overspeed, seems the limits are around18,000. Readig the specs it's clear the Brise units od not start working until 2k rpm and using the site Jonathan linked to mine is running more like 1600rpm. Using the site again seems to suggest a 55mm pulley will solve it for me

I've been caught out twice, once at the Dunsfold handling day and the weekend just gone for the Supercar event, both events involved some spirited driving followed by queuing where the fan is running for some time, the small Powervamp battery doesn't last long.

[tomwood]

Mark,

I managed to find a post from the old forum where I was discussing my experiences:

http://www.lotus7.club/forum/i-seem-have-dynamo-problem

So in summary, at idle I get a little over 12v at the battery terminals which is probably enough to not deplete it but not enough to charge it up.

like you, and I believe this is another Duratec trait, my fan is on a large proportion of the time. The moment I come to a standstill or crawl in traffic it comes straight on and it's enough to drain the battery slowly. Caterham suggest it's normal but I think there is probably only a couple of degrees difference between the thermostat opening temp and the fan cut in temp so it's bound to happen really.

I'll have a look at that site and see whether a smaller pulley could be made to work. Mine revs to 7300 so not that high really.

Tom

 

 

 

 

[Jonathan Kay]

Yes if you blip the throttle it'll charge but as soon as it goes back to idle the charging stops (volts go back to 12.

I think that there are some reports that blipping causes the voltage to stay higher than it was even when the speed has dropped down. I've never understood that effect.

Interesting that the window of success is so tight on some cars. So far we have the suggestions that this is caused by the need to avoid overspeed beacuse the dynamic range is so high, and by the need for the fan to be on so often. Any other ideas?

Does anyone make a speed-limited pulley?

Jonathan

[F355GTS]

Brise have confirmed that their units don't start charging until 2k rpm (Alternator speed) They do a 57mm Pulley which looks like the way to go for me

[Rob Walker]

I have always used the Cosworth Alternator pulleys  Part no YDO 310  and they are 64mm  I think Caterham also use the same.  Never had any charging issues at tick over again with the Nippon Denso small alternator which is off a Diahatsu Charade , brise rotate the field Coil to get the connection terminal in the right place and also use some grub screws to secure field coils other than that its the same.

 

Rob

[F355GTS]

Hi Rob

Do you know the crank pulley size you're using

 

thanks

 

Mark

[Shaun_E]

I'll have to check my pulley size (won't have time until next week I'm afraid) but I have the reverse problem in that my alternator spins at 20k rpm at max revs (8500) and the alternator is rated at max 18k. However, I've been assured it's OK and, touch wood, it hasn't blown up yet.

It's typical of high revving engines (I had the same problem on my big K) that the alternator either doesn't charge at low RPM or is beyond stated operating limits at max RPM. I guess you need to decide which end of the spectrum you want to risk  .

[Rob Walker]

I have only ever used the stock Ford crank pulley that has the harmonic damper and timing wheel they are 130mm

[Jonathan Kay]

Interesting numbers. If the dynamic range of the alternator is greater than that of the engine then you should be OK... if you can get the precisely sized pulley ratios.

But no-one has added quite enough data yet. We need:

1. Intended idle speed (which will prevent discharge under high load)
2. Maximum engine speed
3. Minimum alternator speed to generate enough oomph
4. Maximum permitted alternator speed.

Taking Shaun's dilemma... if those are 1,000, 8,500, 2,000,18,000 (rather than 20,000) then it should be just OK as the dynamic range for the alternator is 9 and for the engine is 8.5.

Anyone got all 4 numbers to check? What's your maximum engine speed, Mark?

Jonathan

PS: There is a workaround... a variable idle speed...

[Rob Walker]

Using the 130mm crank pulley and 64mm alternator pulley gives roughly 2x crank rpm so recon on the red line being around 7500 to 8000 rpm= 15,000 to 16000 alt revs.  At tickover 800 rpm will give you 1,600 which should keep the charging light out

[Nigel Riches]

Jonathan, the increasing rpm and voltage triggering thing is down to a hysteresis in the Gubbins in the alternator, ie, at idle ign light on, give it some rpm, circuit latches on, reduce rpm, circuit holds due to not crossing the, "drop out"  point.

Nigel.

[F355GTS]

Jonathan

Your numbers are right for me ie 1,000, 8,500, 2,000,18,000. I need to check my crank pulley size and using the site in the linked thread you gave above I can calculate the need.

Rob

THanks Rob, 1600 does indeed put the light out but it's not charging the battery and if the fan is running it's being drained

 

Shaun

Thanks for the feedback, I'll watch the upper limit

 

 

[Jonathan Kay]

Thanks, Nigel. I've seen that explanation but I don't understand what's happening at the electronics level.

Jonathan

[Rob Walker]

Mark ,

Sounds  like your alternator is not functioning well as I would have expected it to be producing usefull output at anything abouve 1500 rpm, or is of a different spec to those that I have used, I have built several cars + engines with the 130mm CP and 64mm AP and the Nippon Denso alternator off the Diahatsu Charade and the Edge Alternator/Cambridge M/sport and never had any issues of non charging at tick over.

 

Rob

[F355GTS]

Hi Rob, Brise cofirmed they don't charge until 2k rpm (Alternator speed) and mine seems to confirm this. my crank pulley is 130mm so it looks like the Cosworth pulley you kindly listed is the one for me, at 1k rpm idle (engine speed) it'll give me the 2k Alternator speed

[Paul Deslandes]

Jonathan

the so called ignition warning light is connected with one side to battery potential and the other to a secondary output from the alternator, provided by a second set of rectifiers (sub diodes below) whose main purpose is to power the regulator.  If the alternator is running at too low revs, the secondary output voltage remains below the battery voltage and the lamp stays on.  The regulator controls the alternator output voltage by pulsing the field current on and off - the more power/higher voltage developed by the alternator with increasing revs, the less proportion of the time the field is energised, depending on demand.  I'm not sure whether the hysterisis that Nigel refers to is control hysterisis in the regulator or the regulator simply not powering up until the shaft reaches a minimum speed.

Image below is an Hitachi alternator on a boat engine.

Paul