Craigorypeck
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| posted on 26/3/13 at 11:22 PM |
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High revving alternator
On my second alternator in a short space of time... 
Using a lucas on the side of an YB revving to 8K so alt is hitting at least 16k I think, maybe more
A bigger pulley would bring down the revs but what would be a safe limit?
I'd like to keep the pulley I have and stick it on a high revving alt if possible, any suggestions??
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jeffw
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| posted on 27/3/13 at 07:18 AM |
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You need to work out what it is doing now by using the ratio between the crank pulley and the Alternator Pulley. Once you have the figures
you'll know what the best approach is. High revving alternators are available but tend to be motorsport related and hence are big bucks, much
cheaper to change the pulley.
www.brise.co.uk as an example.
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snapper
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| posted on 27/3/13 at 07:44 AM |
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Cams rotate at half crank speed so I suggest your alternator is not running at 16k
Alternator pulley is usually larger than crank but may be smaller than cam
Yes larger will slow the alternator
Another big killer of alternators is heat, air is drawn through from the rear so a heat shield at the rear to reflect manifold heat and ducted air to
the rear of the alternator helps, I know cause I've done this after similar alternator failures
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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jeffw
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| posted on 27/3/13 at 08:03 AM |
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quote:
Originally posted by snapper
Alternator pulley is usually larger than crank but may be smaller than cam
Really? Most Zetecs have a 132mm pulley and run 60-80mm Alternator pulleys. The Alternator rpm is dictated by the speed of the crank and the ratio
of crank pulley/alternator pulley so could easily be 16K plus on a 8K engine.
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designer
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| posted on 27/3/13 at 08:49 AM |
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I would just change the pulley to reduce the revs.
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jeffw
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| posted on 27/3/13 at 09:19 AM |
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indeed.
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Oddified
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| posted on 27/3/13 at 10:16 AM |
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Been there and got the T shirt!.
Got through many an alternator myself (8750 rpm limit on my NA Cosworth) and a bigger alternator pulley cured it. It seems that the max most
alternators can go to safely is around 15000 rpm.
Increase the size of the pulley but don't go more than you need to (work out the pulley ratios to put the alternator at 15000 on the engine rev
limit) or the alternator struggles to generate much at engine idle (not a problem until you have the headlights on, rad fan kicks in etc) and you
might need to blip the engine when first started to trigger the alternator/put the ignition light off.
Ian
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Craigorypeck
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| posted on 27/3/13 at 10:28 AM |
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From memory the alt pulley is 62mm and the crank is 136 so im over a 2:1 ratio with revs. Where can I get an oversized pulley?
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jeffw
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| posted on 27/3/13 at 10:34 AM |
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mm 1000 8000
60 2267 18133
64 2125 17000
68 2000 16000
72 1889 15111
76 1789 14316
80 1700 13600
84 1619 12952
Using 136mm crank you get these figures. I suggest you need around 80mm to get excitement at idle and under the 15K rev limit. Brise supply
alternator pulleys.
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snapper
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| posted on 27/3/13 at 11:13 AM |
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My mistake (early morning) I'm thinking cam belt not auxiliary
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Oddified
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| posted on 27/3/13 at 11:16 AM |
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I would suggest not going over 76mm as i found that anything bigger and charging at idle is an issue. On yours at 8000 rpm it's nicely inside
the recomended limit of most alternators. I dropped mine back down to a 76mm because of the charging issues at idle and even though it will over speed
the alt at the rev limit it's been ok for several years now.
Manufacturers recomended max rpm is 15000, but 16000+ seems to be when they will die from what i've found.
Ian
[Edited on 27/3/13 by Oddified]
[Edited on 27/3/13 by Oddified]
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britishtrident
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| posted on 27/3/13 at 12:29 PM |
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Usually when alternators fail due to high rpm the rotor windings break where they enter the crimped connectors to the slip rings, it might be
worth dismantling the alternator to do a forensic investigation. I have seen a couple of factory big name (Valeo) re-manufactured alternators
fail at this pint because the end of the rotor winding were mechanically damage at this pont during manufacture.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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40inches
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| posted on 27/3/13 at 12:43 PM |
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How about an alternator from an engine that runs at 8000rpm, S2000?
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jeffw
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| posted on 27/3/13 at 02:24 PM |
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quote:
Originally posted by Oddified
I would suggest not going over 76mm as i found that anything bigger and charging at idle is an issue. On yours at 8000 rpm it's nicely inside
the recomended limit of most alternators. I dropped mine back down to a 76mm because of the charging issues at idle and even though it will over speed
the alt at the rev limit it's been ok for several years now.
Manufacturers recomended max rpm is 15000, but 16000+ seems to be when they will die from what i've found.
Ian
[Edited on 27/3/13 by Oddified]
[Edited on 27/3/13 by Oddified]
Each alternator will have its own switch on or excite rpm. Ideally you would work out the top rpm and bottom rpm so it would excite on idle and not
over speed at max rpm. However even if it doesn't excite at idle a quick blip will switch the alternator 'on' and it will stay on
until the engine stops.
A lot od the Denso alternator will go to 18K rpm.
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Oddified
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| posted on 27/3/13 at 04:07 PM |
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quote:
Originally posted by jeffw
quote:
Originally posted by Oddified
I would suggest not going over 76mm as i found that anything bigger and charging at idle is an issue. On yours at 8000 rpm it's nicely inside
the recomended limit of most alternators. I dropped mine back down to a 76mm because of the charging issues at idle and even though it will over speed
the alt at the rev limit it's been ok for several years now.
Manufacturers recomended max rpm is 15000, but 16000+ seems to be when they will die from what i've found.
Ian
[Edited on 27/3/13 by Oddified]
[Edited on 27/3/13 by Oddified]
Each alternator will have its own switch on or excite rpm. Ideally you would work out the top rpm and bottom rpm so it would excite on idle and not
over speed at max rpm. However even if it doesn't excite at idle a quick blip will switch the alternator 'on' and it will stay on
until the engine stops.
Absolutely, but even with the ign light out the alternator output is still governed by it's rpm if it's turning very slowely at idle. I
found with a pulley of 80mm, an idle of 1000rpm and most electrical things turned on that the current drawn from the battery was more than the
alternator would produce (slowely flattening the battery by the difference) without raising the idle slightly to 1100 - 1200rpm or reducing the pulley
size slightly. With a voltmeter and ampmeter on the car it's quite easy to see what's happening.
Ian
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jeffw
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| posted on 27/3/13 at 06:29 PM |
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Brise's ACR they list on the website makes 17 Amps at 1500rpm (alternator rpm) and 34Amps at 2000rpm upto a peak of 62Amps at 7K rpm. A 76mm
pulley would give you the correct range of rpm for your likely needs (given that we don't know which alternator you have).
Make sure when you buy a pulley you get the offset you need and the correct shaft size (normally 15 or 17mm)
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Oddified
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| posted on 27/3/13 at 07:54 PM |
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As standard the cossy engine has twin belts/pulleys. I never found over size double pulleys for the alternator so i ended up machining my own up. If
your just using one belt then it's simples
Ian
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Craigorypeck
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| posted on 27/3/13 at 10:21 PM |
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Hi all.. The alternator is a crappy lucas one that most pintos have, my dad got a new alt for his JCB and it was the same one lol! (well it looks the
same....)
Just checked the pulley size and I was right in the earlier post.
At idle the light flashes over and surges. checked all connections and clean up all contacts too.
so just googling on lucas alts it appears they have a max rev limit of around 13000rpm.
I'm running serpentine pulleys as the eaton charger is in the loop too.
As i need a new alt and custom made serpentine pulley it may be cheaper getting an uprated more modern unit that will work at both ends of the rev
range.
I'll have a look at brise and see what they have to offer.
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Craigorypeck
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| posted on 27/3/13 at 11:13 PM |
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£300 via brise, bit outta price range there..
so who has fitted a standard off the shelf denso say like this...
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140912629363&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en
i have a few spare alt mount blocks that i could modify to allow fitment between lugs.
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starterman
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| posted on 29/3/13 at 03:24 PM |
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I do believe the Lucas number he is quoting for that unit (LRA 2814) is a Ford smart charge unit and not suitable for what you require. The Alterntor
you have I think is a Lucas A127 rated at probably 65 amps. These are available in a 120 amp version. I would however think that a 70 amp A127 with a
larger pulley would be more than ample for you needs and have been fitted to a pinto running to just over 8,000rpm.
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Craigorypeck
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| posted on 29/3/13 at 06:23 PM |
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I think i may know why i'm having trouble!! it says china on the rear bearing, cheap chinese knock off copy!
thanks for all the replies and help lads, will prob source a genuine unit and get a larger pulley.
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