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 Post subject: Reverse Mount Alternator
PostPosted: November 16, 2015, 3:24 am 
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Due to space constraints, I’ll be reverse mounting an alternator on my LS3 which will put the alternator into counter clockwise rotation. While this won’t affect charging, I’m concerned about airflow and cooling, as at least some alternator models have directional fans. Rumor has it the cooling airflow is directed primarily to the internal electronics.

Seems fan packaging comes in several configurations: external fan only, internal fan(s) only, and internal plus external fans.

External-only fans are easy to read for preferred rotation direction. And if a suitable replacement can be found, the fan could be swapped out for a CCW version.

Internal fans are difficult to read for preferred rotation direction without tearing the alternator down, so they remain a bit of an unknown.

If an external fan was swapped out on a combo internal/external fan unit, the airflow could be fighting itself resulting in little cooling.

I have found a billet reverse flow fan available through a Corvair site. And baffle disks are available to “end plate” external fans which should help improve airflow even when running “backwards.”

IIRC, earlier Honda motors ran in a CCW direction, so their Denso alternators could be candidates.

I haven’t bought an alternator yet, so my options are open at this point. To fit, my alternator will need to be a relatively compact unit with enough generating capacity at idle to support fuel pump, electric fan, electric water pump, ignition, injectors, ECU and lights. I’m thinking I’ll need at least a 60 amp capability at idle. While there are a number of alternators that would fit most of the criteria, the CCW rotation limits my choices if indeed there is a cooling issue when running an alternator backwards.

Interested in your comments, suggestions, pointers, etc. Thanks!

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PostPosted: November 16, 2015, 10:33 am 
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If a fan is a centrifugal unit it will work running in either direction, and will produce flow in the same direction with either rotation. Whether the 'blades' on that fan are purely radial or are skewed forward or aft (relative to rotation) will affect flow rate and noise levels when rotation is reversed, but the fan will still move air. Obviously, an axial fan works backwards too, but will reverse flow direction, and depending on the elegance or crudity of design (not only of the fan, but of the alternator flow passages) may or may not affect flow rate. My memory suggests that most alternator fans are centrifugal ....

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PostPosted: November 16, 2015, 1:12 pm 
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Not sure if it meets your requirements but the Jaguar E type came with a reverse mounted alternator from the factory.

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PostPosted: November 16, 2015, 1:18 pm 
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If you have a local starter/alternator rebuilder. Tap into him for advice. They usually know what can be swapped from one to the other etc. And they generally have cores to get parts from. Then buy from him for all of his sage advice. I find they are very competitive.

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PostPosted: November 16, 2015, 2:17 pm 
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On a lot of internal fan alternators, you can peer through the little slots and, with a flashlight, while rotating the shaft, you can see the fan blades. I just went through this exercise, and was concerned that the ND alternator I intended to use (from a Suzuki Swift) appeared to have its fan blowing from rear-to-front when spun in the engine's normal direction of rotation.

I took it to a professional rebuilding shop (as two of its diodes were shorted to ground when I got it) and, while I was there, I asked them about this issue. The technician pointed out that, contrary to my assumption, alternators are normally built to pull air from back to front, rather than front to back (as you'd expect air flow to travel in an engine compartment).

If you find yourself wanting to use an alternator that cools in the opposite direction from what you want, I'm sure that if you can run a small duct to the alternator that brings cooling air to it, that will probably work. Of course, the higher the output of the alternator, the more heat will be generated around those heat-sensitive diodes...

Alternatively, is it possible to route the belt differently, so that it runs on the other side of the pulley (you'd need a plain, rather than ribbed, pulley for this)? If you have enough wrap around the pulley, it'll work just fine, and you can then spin the alternator in its intended direction. I could have done this (and was planning on it, until I found out about the cooling direction for my alternator), although I'd have had to add another idler pulley to do it.

In my case, the OEM Ford alternator was intended to be used with the original car's ECU, and would have put out a constant 16V without it (I don't have an ECU at all in the Locost). Plus, the OEM alternator ended up with the belt run going right through the middle of my new ignition pickup sensor & cable, so a new-to-me, different alternator in a different location was necessary. Of course, in the new plan the sensor was fine...but the alternator fouled the oil filter. But that's another story!

The ND one I picked up at a wrecker apparently puts out 80 amps max (I don't' know what it makes at idle), is a 3-wire (so it WILL charge at idle), it has a wire for a warning light (something I want, after past issues on other cars!), and it's VERY small, which helps a lot in packaging.

Just throwing some ideas out there...

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PostPosted: November 16, 2015, 9:16 pm 
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if the fan draws air in the front in normal rotation, then it will draw air in the rear in oposite rotation, so if you mount the altenator facing the wrong way it should be fine.

was this a trick question?

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PostPosted: November 16, 2015, 9:58 pm 
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John, that is only the case for axial flow fans - but that is what it may be I suppose.

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PostPosted: November 16, 2015, 10:34 pm 
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My understanding is that, if the alternator turns the wrong way, heat from the alternator is blown onto the heat-sensitive diodes, rather than cooling air. The diodes can be expected to fail prematurely that way, although it would be okay for a while.

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PostPosted: November 16, 2015, 11:20 pm 
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seattletom wrote:
earlier Honda motors ran in a CCW direction, so their Denso alternators could be candidates.


The 90's Honda option is your best bet, IMO.


zetec7 wrote:
My understanding is that, if the alternator turns the wrong way, heat from the alternator is blown onto the heat-sensitive diodes, rather than cooling air. The diodes can be expected to fail prematurely that way, although it would be okay for a while.


The direction of air flow won't change.

Centrifugal fans pull air from the center to the outside regardless of which direction you spin them. With straight vanes they flow exactly the same CW or CCW. With curved or angled vanes they work well when rotated as they were designed to, but flow substantially less air when you run them backwards.

If an alternator with a curved vane fan is run backwards the air still moves in the intended direction, there's just a lot less of it. Leading, sooner or later, to melted insulation and a terminal loss of magic smoke.


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PostPosted: November 16, 2015, 11:54 pm 
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That's it, exactly. My NipponDenso has curved vanes - spinning it one way provides noticeable air flow, and very little when turned the other way. When I got my ND alternator, it seems that someone else had already let the smoke out, so I had to take it to "Ye Olde British Smoke-Infusion Shoppe" to get it put back in & plug the leak... :roll:

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PostPosted: November 17, 2015, 8:52 pm 
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Thanks guys, great input and suggestions. I feel schooled enough to go visit a local alternator rebuilder (or two) and carry the discussion on to the next level. I'm thinking an ND from a CCW 90's Honda makes a lot of sense. Need to find one that will put out at least 60 amps at idle, though, and 90+ amps at speed. Powermaster has some nice race-prepped Denso units that could work, but they aren't in the budget. At least their amp rating could be trusted.

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PostPosted: November 17, 2015, 9:46 pm 
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Quote:
capacity at idle to support fuel pump, electric fan, electric water pump, ignition, injectors, ECU and lights.


I think 60 amps at idle would be overkill. The injectors are not firing for a long time and the coils are going slowly, so these are only a couple of amps. Having a number for the electric water pump would be good. Headlights usually have a watt rating so that will help too. Watts are equal to volts times amps. The ECU is only about an amp.

The flip side of the coin is with a car like this you actually want to be seen pushing it along whenever you are stuck in traffic. It speaks to a young man's dedication to sport in the face of obstacles. DId Hercules worry about his amps? No, he laughed at his obstacles.

Also consider being seen riding a stationary bike next to your car on the side of the road with a generator connected to the car with jumper cables!

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PostPosted: November 18, 2015, 1:53 am 
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horizenjob wrote:
Quote:
capacity at idle to support fuel pump, electric fan, electric water pump, ignition, injectors, ECU and lights.
I think 60 amps at idle would be overkill. The injectors are not firing for a long time and the coils are going slowly, so these are only a couple of amps. Having a number for the electric water pump would be good. Headlights usually have a watt rating so that will help too. Watts are equal to volts times amps. The ECU is only about an amp.
The flip side of the coin is with a car like this you actually want to be seen pushing it along whenever you are stuck in traffic. It speaks to a young man's dedication to sport in the face of obstacles. DId Hercules worry about his amps? No, he laughed at his obstacles.
Also consider being seen riding a stationary bike next to your car on the side of the road with a generator connected to the car with jumper cables!
Marcus, you're right, it may be overkill on my part (again.) However, the fuel pump, water pump and radiator fan can pull a combined (rated) 43 amps. Throw in some juice to fire the engine and then turn on the lights. Sneaks up towards 60 amps and I'm not planning a big battery for reserve. Roll bars are handy push handles, though. Don't ask me how I know. :oops:

So the next step is to see what the physical sizes of the various alternator options look like by visiting a rebuilder. I plan to mount the alternator at or below crank height on the drivers side, out of sight. Steering linkage is a minor obstacle to avoid, but I'm not a fan of high mount alternators. The last time I did one of those was with an old school generator atop a flathead motor. 8)

Dug into the ND factory alternator on-line catalog tonight, cross-referenced Honda models with CCW motors and linked to pictures of their alternators. Lots to chose from, from 45 amps (max) to 110 amps (max.) No spec on idle amps, though. The position of the lugs and stud on the case are important for the mount I have in mind, so it was a productive bit of research. My favorite right now is from a 1995-96 Acura TL, 110 amps max. It might be a little bulky, though. We'll see.

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PostPosted: November 18, 2015, 2:38 am 
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Quote:
fuel pump, water pump and radiator fan can pull a combined (rated) 43 amps.


Yup, that's a lot, so your doing right looking for 60 amps. How much does the water pump draw?

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PostPosted: November 18, 2015, 3:26 pm 
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seattletom wrote:
My favorite right now is from a 1995-96 Acura TL, 110 amps max.


You're referring to the 2.5 TL and not the 3.2 TL, right?


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