Low voltage after installing electric fans

I recently battled an overheating issue (new (used) engine) that I addressed in another thread, realized I didn't have any fan shroud, decided it was better to go with electric fans out of a Suzuku XL7 than to hunt down and pay for the right shroud. They have been working well, keeping me cool, but this week I was stranded with a low battery after driving across town, which caused me to test my voltage/alternator situation. I'm good without the fans on, but when the thermal switch turns the fans on (which usually then stay on for the duration of my trip), my voltage drops to ~12.2 at 650 rpm idle, measured with a good voltmeter. It slowly increases as I rev it up to 1150 rpm, then is at the minimum 12.7. This is obviously way too high for hot (curb) idle, so I figured the alternator in there was an older ~35A unit and wasn't able to keep up with those fans. The fans don't trip their 30A breaker, but I have no idea what amperage they're really drawing and am not confident in that cheap breaker's accuracy- it might be more than 30A.

I swapped the alternator with a parts store 55A unit, hoping it might be an upgrade. It even had a smaller pulley than my original. The behavior was exactly the same as far as I could tell. Driving around my cheap in-car volt meter barely ever went above 12V.

At this point, I'm not sure what to think. I know alternators tend to have trouble at low RPM producing amps. But both the old and new alternators in my case are giving what I would consider weak voltage up in the 1150 rpm range and even while giving it full throttle while driving (I don't have a tach in the car, so I'm not sure how high that's getting, but the cheap voltmeter is reading ~12.5V at full throttle acceleration with those fans on. 11ish with the lights on also). So, maybe my battery is weak and is pulling my voltage down in all conditions? This is my primary suspect that this time. Or, the Suzuki fans are using a crazy amount of amps that both the old, and new 55A alternator are having a hard time keeping up with. Seems unlikely. Or....? Maybe my original external regulator is not working properly? A longer test drive around the neighborhood with the new alternator left my battery, back in the driveway, turning my starter with no problem, and the battery at the expected 12.4V.

Ideas? Yank all this electric fan stuff out and hunt down the right shroud? I still have the fan spacer/fan. Get a high amp alternator? I've heard they have the same trouble at low RPMs, plus I'd have to upgrade a bunch of wiring. A smaller alt pulley won't help- even at 1150 rpm I'm not getting enough amps...

 

Do it properly and source a factory clutch fan and shroud. The ONLY reason factories use electric fans is space savings, OR the engine is sitting the wrong way. Electric fans DO NOT cool better than an engine driven fan, they ARE better at causing headaches tho

 

Alternators are rated to provide the rated amperage at a specific shaft speed (usually around 6,000 RPM of the alternator's shaft speed).

Yes, at idle and low engine RPM, it may not produce total rated amperage.

And you must take into account every item loading the electrical system, from charging the battery, (which takes a good bit of amperage over a very long time, and the "charging curve/maintenance load to keep it charged), as well as number of times charging is less than the draw of the battery, amount of draw over time, that can be higher than the recharge rate.


Fans cutting in and/or ramping up (it modulated) can create high momentary draws above their continual run at full RPM ratings.

Even if you calculate the total amp demand on your car at highway speed, and it is say 40 AMPS, and your alternator is rated at 55 AMPS, you can still end up undercharging the battery due to the variables mentioned. Having a proper and good working electrical wiring, as well as proper regulator, you can run a much higher rated alternator.

But, increasing the alternator to a much higher output and not accounting for the higher amp drawing, you can have problems with overheating wires, melting connections, damaged accessories or fire. And the battery needs to be sized accordingly to demands for load as well as being able to take higher discharge/recharge rates.

Fuses and circuit breakers can operate even if load is larger then their rating, if the load is momentary and not greatly higher than the load.

Auto-resetting breakers can function longer in such conditions because they are thermal, and need time to heat to break. Small over limit can result in not tripping, where a short but very high condition will trip it faster. So trying to equate a 30A breaker is connected to a fan that is less than 30A because the breaker is not tripping, is not a reliable indicator.

Fuses tend to be quicker response, (but also can blow too fast with some accessories due to spikes that are very high, where a breaker would be more logical protection.

Do you know what the fans are rated at? And what, if any accessories or components do you power that are not original to the car? Like ignition, Electronic Fuel Injection, audio, lighting etc?

 

Exactly need to ditch the old external alt,..

 

https://www.dbelectrical.com/products/high-output-chevy-one-1-wire-alternator-105-amp-10si-se.html

I have 1 of these on my racecar.....makes solid 14 volts at idle.......about 900......thatd running 3 very large electric fans and a very large fuel pump, plus all my ignition stuff.

In fact I can race a 3 day event with charging.......and if I do put one on in the evening or morning it might run like 10 mins then kick off....


I did have to re clock mine but no big deal just hold the brushes....remove 4 screws and turn to fit

 

Check the ground on the voltage regulator. Some voltage regulators are adjustable. Maybe someone can tell you how to tell. I believe it’s got to be a delco unit. Try to full field the alternator. That should tell you if the alternator is capable of putting out more. Or if the alternator need to be replaced

 

I went through exactly the same thing with dual electric fans. Probably have a thread on it here from back in 2011-12 maybe. Even after a 100 amp internally regulated alt I was still draining the battery and overheating the car on anything more than a 50 mile trip. Went back to the clutch fan and factory shroud.