# Higher AMP at Lower RPM - Alternator



## [email protected] (Aug 6, 2014)

Hi,

I am not sure whether this is the right place to post this question but if you can post a reply I really appreciate it.

I am having a 4DR51 Engine and the alternator is 25Amps 24V. But I need additional 50AMP output. Therefore I changed the stator of the alternator to produce more current and as usual now it needs higher RPM to start generating. But the idle RPM is around 600 and at that range the existing alternator is not able to produce any amount of current due to higher gauge stator. 

What I am considering is to have another permanent magnet alternator (Dynamo) attached to the engine pulley so that it can give the additional required power. But I do not know it is the best solution. If you have done this before please help me to decide. Thanks.


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## dougingraham (Jul 26, 2011)

This is a forum for converting vehicles to electric power. You should probably look elsewhere for a solution to your problem. However this is what came to mind:

Put a smaller pulley on the alternator. That will increase the RPM which will allow it to come up to voltage sooner and allow it to generate more current with your modified arrangement. This might not work because there are electronics involved with alternators which adjust the field voltage to control the output current.


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## [email protected] (Aug 6, 2014)

First of all thank you for your reply. Apologies for posting this on here. 
I have done the pully conversion to increase the rpm. Kindly let me tell what I have done. 

Change stator coil to higher guage one. 
Make it delta.
Remove the manual cut off and apply IC regulator
Pully cconversion up to maximum possible. 7×2.5 inches

Still it doesn't generate at engine idle time. 
Will I have to upgrade the alternator I mean the whole unit? Or do I have to make it dual alternator powered. ?

Appreciate your help on this. Thanks.


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## dougingraham (Jul 26, 2011)

A generator (alternator) generates voltage as it turns and the faster you spin it the higher the voltage. There are control electronics that vary the field strength to modify this somewhat. If you change the internals to increase the output voltage, this will lower the current output. If you change the internals to increase the current output you will lower the output voltage. The design of an alternator will be to output a certain max current at a particular voltage over a particular RPM range. For typical alternators this is up to 14.4 volts. If you need more current because of additional loads the best thing to do it replace the alternator with a heavy duty one. One of my internal combustion engine cars has a 60 amp alternator and it is considered marginal. At night with the lights on and the wipers running and the defroster going and the rear window defogger going it can't keep up. Large trucks have much larger alternators (150 amp). These are generally peak ratings and they cannot sustain that for long periods. The goal in an ICE is to recharge the battery quickly right after start which means only a few minutes of operation at full power.

You should probably look for a forum that caters to the reason you need to modify your charging system. They will have experience and hopefully answers for your issue. I don't think trying to modify an existing alternator is going to in general be productive. They are designed for a particular output and most of the things you can modify will hurt the output rather than increase it.


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