Time for a new alternator?

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I was testing a SMPS in my car today and was a bit shocked at the results.

No load - in 14.4v / out 98v
10R load - in 11.3v / out 64v

64v^ / 10 = 409.6

So, with a ~410W load my charging system dropped to 11.3v. Does this sound normal for a stock ~70A alternator at idle?

I'm leaning toward the alt is OK, just underpowered. Either way I'm going to buy a new alt; I'm just wondering if it's worth breaking the bank for a 160A unit.
~700RPM idle. I'm going back out to the car to see what the voltage drops to with the engine held at 2K.

I think generally an alternator will put out 40-50% of its rated current at idle.

EDIT: Done. The results were pretty much the same, even at 3K. Also, two 10W 20R resistors in parallel cannot survive for more than 4 seconds at 64V:hot:. Time to find a new load.
Ahha, definitely a wire problem. The voltage at the battery is 12.6v while the voltage at the supply is 11.15v. This is with the new load I made that is just under 10R.

I would like the try the supply connected directly at the battery, but there is a bit of a snow storm out right now.:(

Does 12.6v sound more reasonable for a 410w load?
same thing happens to mine. car is toyota rav4.

although, when the alternator is cold, at 750rpm, voltage is 14.3V. when alt heats up, drops down to 13.8V. when loaded with about 1KW or so, voltage drops to 12.2-12.4V (I have a truck battery under the hood) athough alternator output does improve when we get to 1500rpm and up.

you will probably not have problems when the amp is driving a speaker load and music signals, your ears wouldn't like the torture anyway. :D as I understand, in that test, your SMPS is directly connected to the load...
Yeah the 10R load was connected directly to both rails.

Below is a pic of the supply. TL494, 16x IRFZ44N (soon to be HUF75337P3), 8x 1mm primary, 3 x 1mm secondary, 10,000uf 71v per rail.

This will powering a 2R BTL via Tripath TDA2500 with 80A fets. There is about a 90% chance I blow something up.:D

An externally hosted image should be here but it was not working when we last tested it.
The amp section that used to be attached had 10 pairs of A1694/C4467. It would run 1/2 stereo or 1 ohm BTL with no problem. The thing was an inefficient current hog though.

What do you think about taking the outputs of the transformers and making a +/-90v supply instead of +/-45v? Then run 4 ohm stereo?
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