HO Alt Output @ Idle RPM

[boister77 10+ year member]

is it normal for a ho alt to produce low voltage/amp at a low rpm? i've been told this is normal since ho alt work differently. however, i just want to get more opinions. also, i got my electrical system checked by three different places and they all said at idle, there is actually a negative amp reading.

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[BooLeaN 10+ year member]

That is weird, but yes kinda usual.

The alternator usually kicks on at a certain RPM and yours probably kicks on higher than idle.

Most alts I have seen do less than 1/2 their rating at idle.

Mine is a 200 amp alt and does 172 at idle though //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[BIG_SUPERMAN72 10+ year member]

How much for a new 200 amp alternator?

 

[BooLeaN 10+ year member]

I got mine for 320 USD shipped. I went to Rob V.O.

vvanoverdyk@shaw.ca

Great guy,

Thanks,

Craig G

 

[InhumanAcura 5,000+ posts]

That is weird, but yes kinda usual.
The alternator usually kicks on at a certain RPM and yours probably kicks on higher than idle.

Most alts I have seen do less than 1/2 their rating at idle.

Mine is a 200 amp alt and does 172 at idle though //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

The alternator is on as long as the motor is running. The faster the the motor spins, the faster the accessories spin, therefor the alternator does more work (creates more current). Im confused on the negative charge that the shops found?, I find it hard to believe that the RPM being at idle changes the positively charged electons to a negtive charge. If you were to put a different size pulley on the alternator or even raise or reduce the size of the other pulley's the rate of charge at idle would differ.

 

[DirtySchemer 10+ year member]

Maybe he had his engine in reverse? Yeah, I agree that a negative current would be pretty impossible.

 

[BooLeaN 10+ year member]

The alternator is on as long as the motor is running.

This depends on the alternator. Some alternators use a 2 or 3 wire configuration and one of the wires is a power wire, goes to the battery and the other wire is the one that tells the alternator to turn on. The 3rd wire is???/

A lot of High Output alternators use a 1 wire setup. This is a self exciting alternator and it begins to work at a specific RPM. Once it's pully is rotating quick enough the alternator kicks on and begins producing power.

It is possible that his alternator isn't kicking on until above idle. I'm not saying it IS the problem but it is a possibility.

Thanks and good luck,

Craig G

 

[boister77 10+ year member]

thanks for all of the advice. definitely helpful! i noticed that my amp/voltage rises as i increase rpm. i was wondering, if i am stuck in traffic (live in los angeles area so it's a daily event) will it kill/drain my battery since the engine will be at idle speed for a good amount of time? thanks!

 

[BooLeaN 10+ year member]

IF the alternator is actually not on, then YES it will. If the alternator IS on, then you will be fine.

You would probably know really fast if the alternator actually isn't on, I'm not sure how long the battery would last but an alternator died in one of my cars once and it didn't last more than 10 min before the car was dead. That could be because the battery might have been already low??

Either way, the voltage with the car off should be 12ish volts, from your battery.

Turn the car on, if the alternator is working it should read aroun 14ish volts dependino on the specific alternator.

If you still get 12, then the alternator either isn't on, or is just slightly on, but all of it's power is consumed.

If your car uses (just a wild guess) 30 amps at idle, your alternator might produce 25 amps at YOUR ENGINE'S idle. You would then have a negative 5 amp draw, IE your battery is dying.

You can probably talk with the company that built your alternator, ask them how much power it puts out at idle. Tell them what your car idles at, I'm pretty sure in park, most cars are around 1200 ish RPM and in drive 900ish RPM.

Hope this helps,

Good luck,

Craig G

 

[boister77 10+ year member]

thanks boolean! very helpful info you have!

 

[BooLeaN 10+ year member]

No problem //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Glad I could help out a bit anyways.

Good luck,

Craig G