19 replies to this topic

[Midas Mk1]

Hi all,

 

I've got one of these powerlite lightweight alternators fitted to my MPi (hybrid earlier a+), and have noticed on the way to work this mornign its only charging when im above 2.5-3k revs. Had my headlights on, and in the 50mph average zone my voltmeter was dropping to just under 13, when at idle its 12, but anything  over 2.5-3k its 15v.

 

Is this the norm for these types of alternator? Seems rather strange to me, i'm running the larger water pump pulley, and med crank damper, could it be spinning too slow for the alternator perhaps?

 

Pretty sure its 45W

 

Thanks

 

Sam

 

 

https://www.minispor...abs_description

 

 

[minifreek1]

I dunno if its the norm for this type of alternator, but a normal alternator charges at just on or just over tickover (1000 RPMs)

 

Is it new...?

 

You could always ask at where you bought it from...?

Edited by minifreek1, 11 July 2017 - 06:55 AM.

[ACDodd]

The standard mpi alts is a 65amp unit. Fitting a lightweight race type alt with only 45amp output is your problem. Its too small to provide the required power consumption of your vehicle at lower revs. Its lighter for a reason, it ha add less copper windings and smaller rotor/stator to achieve the weight saving. Race cars use much less power and typically spend most of there time with the engine over 6krpm. A road car does not.
Most modern aternators can provide only 55% of rated output With the engine running at 1000rpm. Therefore you only have abut 25amps of output current to run everything at idle. Using the 65amp unit you have 35amps amps available at the same speed.

Ac

Edited by ACDodd, 11 July 2017 - 07:27 AM.

[timmy850]

The part number corresponds to a 50A unit

http://www.powerlite...roducts/rac068/

[Pigeonto]

Most modern aternators can provide only 55% of rated output With the engine running at 1000rpm. Therefore you only have abut 25amps of output current to run everything at idle. Using the 65amp unit you have 35amps amps available at the same speed.

Ac

I want to fit a small alternator to gain some space so I checked  the draw of what may be switched on at idle. Headlights,heater fan, fuel pump, brake lights,indicators, cooling fan, rear window, radio, and was a bit surprised. Just those total 30.5 A.  Without wipers. Blimey ! I'm still considering how to go about it.

[Midas Mk1]

Cheers for the replies guys, especially AC for your quick response / explanation.

 

Suppose with the specialist components ecu, fuel pump, headlights, clock, sidelights then that could add upto over 25a.

 

Pretty gutted to be honest as its quite expensive and looks great in the engine bay compared to the brick of the standard type. Looks like the only option is to replace then? Unless a smaller water pump pulley might increase the speed of it on idle?

[mini13]

I've seen these in mpis and they have been fine, you don't have any non standard pulleys do you?

[Midas Mk1]

Im running the larger type water pulley, and got the med crank damper and pulley, but im sure that the same size as a normal bottom pulley. 

[panky]

You would need a different alternator pulley to make any difference, a smaller water pump one would just make the water pump spin faster. But not sure if a smaller alternator one would actually work.

Edited by panky, 11 July 2017 - 10:02 AM.

[ACDodd]

Just manage the electrical load. Switch off loads when idling.

Ac

[ACDodd]

Increasing the pulley ratio will improve the situation but at the expense of increased wear and decreased reliability due to increased duty cycle. Your car was fitted with a larger output alt for a good reason. Brush and slip ring wear is noticeley increased when the alt is undersized. You have a number of options;

1 leave as is and reduce the electrical loads, by being more aware of the circuits that ae working when you are driving and reduce loads where practical.

2 increase the pulley ratio and except more regular alt replacements.


3 fit original unit and have no more issues.

Ac

Edited by ACDodd, 11 July 2017 - 10:17 AM.

[Midas Mk1]

Cheers AC! Much appreciated as are the other replies. 

 

Think im gonna have to try cope with it this week getting to work, then get hold of a standard type 65 / 70a bigger alternator, and change the wiring to accept the standard type plug on saturday.

A shame really, but I suppose on this case function > form.

 

Just checked all the wiring, and even have an extra earth on the alternator bracket.. ahh well. 

 

 

Thanks guys :)

Edited by Midas Mk1, 11 July 2017 - 11:26 AM.

[mini13]

do check the output current  if you can, it might be as daft as a faulty alt reg,

 

a freind was runnig one of these on an MPI with a K head and the SC ecu with no prooblems, Ive run one on my mk1 with 7 port and full injection, and 80/100w lights and spotlights with no porblems.

[Midas Mk1]

Hmm, I literally just had headlights on and my radio on standby this morning, nothing else, so thats really got me wondering. As it's an MPi loom it only had two connections not 3 required for the alternator, so i put the third  green switched live to the fusebox, hmm think i'll double check the questions when im home tonight.

 

 

[minisilverbullet]

I run a similar alternator (denso), I have heated screen and 4 x100w spots. 

 

I haven't used it that much (couple of thousand kilometers), seems to work fine!