Reverse-mount 12V alternator

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kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Thu Jul 11, 2019 3:00 pm

pinzi wrote:Or you could go for a second 24v alternator :wink:
Yeah exactly! Whatever you can find in a 10SI case, it shall bolt up.

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Re: Reverse-mount 12V alternator

Post by whitesik » Fri Jul 12, 2019 1:55 pm

Not even close to an engineer here, but how does this tax the already meager HP of the motor? I think that has been a concern in past discussions.
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Re: Reverse-mount 12V alternator

Post by kdiqq » Fri Jul 12, 2019 2:12 pm

whitesik wrote:Not even close to an engineer here, but how does this tax the already meager HP of the motor? I think that has been a concern in past discussions.
There's a couple of ways to figure that out and there are a few discussions on which is best online. From what I can find, the range is somewhere between 4 and 10HP. Since I'm using a smaller 90A alternator, Id say I'm somewhere in 6HP range. You may notice that on a 90HP motor, you might not. There are always tradeoffs with pulling accessories off engine power.

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TechMOGogy
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Re: Reverse-mount 12V alternator

Post by TechMOGogy » Fri Jul 12, 2019 2:53 pm

Lots of post here about trying to run both 24v and 12v and issue with common ground I believe.
Others here with more knowledge than I should chime in!
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kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Fri Jul 12, 2019 3:10 pm

TechMOGogy wrote:Lots of post here about trying to run both 24v and 12v and issue with common ground I believe.
Others here with more knowledge than I should chime in!
Dan
I consulted with an electrical engineer that I work with who has built a few electric motors. He said you can try and keep the grounds split, but the alternator grounds through the case. It shouldn't be a problem. Sounds believable since there are a few guys on the military truck forums who are running dual systems with a common ground without issue.

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kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Sat Jul 20, 2019 10:49 pm

Sorry for the slight delay, I got a little preoccupied helping a friend install a 3" lift... for his Miata. Really awesome project!!
Image

I had a bunch of trouble getting the idler how I wanted it and everything and keeping cost down, but I finally got it worked out and I'm super happy with the solution. The addition of the idler and shaft come out to about $70. A little more than I'd like, but it's beyond automotive grade with dual ball bearings and cast steel construction. Likely could have done nylon and single bearing, but I want to throw this on and forget about it.
Image

I modeled in a rough belt routing to demonstrate my thinking. Pulley diameters and distances are approximate, it's just for illustrative purposes.

Image

One question I asked when going through this was is backside tensioning a v-belt is okay. Short answer is, yes. I contacted Brewer Tensioner (who makes exceptional belt and pulley products) and they said it is doable, but may reduce belt life. The Pinz so far has awesome belt life and I'm thinking with a simplified belt tensioning method, it should be very easy to monitor and stay on top of. Testing will definitely give the best results!

I have a couple additional tweaks I want to make before this next rev hits the printer. Looking forward to getting the system going!
1977 Austrian 710M

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Re: Reverse-mount 12V alternator

Post by Tjerk » Sun Jul 21, 2019 4:15 am

Reverse idlers are hard on belts and some belts are possibly constructed differently than others.
On my John Deere ride-on lawnmower, the OE belt lasts twice as long as a standard Gates belt but is also twice as expensive.
Tjerk

kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Thu Jul 25, 2019 5:28 pm

First revision looks on the money! I'm going to make one tiny adjustment and then hit go on the metal versions!

Going to throw together a bill of materials here soon to get a cost estimate. I'm figuring I'm well under the $1k+ being asked in Sweden... Image

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Andre
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Re: Reverse-mount 12V alternator

Post by Andre » Mon Jul 29, 2019 7:26 am

So how do you plan to eliminate any voltage ghosting through the alternator housing?

Will you be isolating the mount to run a direct ground and power to an auxiliary battery? Or will you have a disconnect switch on the power supply to the existing battery jumper cable?
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kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Mon Jul 29, 2019 7:36 am

Andre wrote:
Mon Jul 29, 2019 7:26 am
So how do you plan to eliminate any voltage ghosting through the alternator housing?

Will you be isolating the mount to run a direct ground and power to an auxiliary battery? Or will you have a disconnect switch on the power supply to the existing battery jumper cable?
The 12v and 24v systems will use a common ground. From all the other dual-voltage setups I investigated, I never saw anything about voltage ghosting. I don't imagine there will be stray voltage over ground in any scenario. The couple of electrical engineers I spoke to had zero concern with the configuration having a shared ground. If it did become an issue, the alternator can be easily isolated thru the mount via a coating. Even powdercoating would work. I plan to run it as is though. I suppose to double check, I could run an oscilloscope on the 24V ground and 12V ground and see what feedback looks like.

FWIW, there is a company, Niehoff, that produces dual voltage alternators for military applications and it runs a common ground with dual outputs with no problems.

For the disconnect, I plan to run a relay on the main switch. When you use the battery cutoff behind the seat, it will trip a relay for the 12v system. I'm open to feedback on if there is a better solution to that, it just seemed the most elegant.
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rmel
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Re: Reverse-mount 12V alternator

Post by rmel » Mon Jul 29, 2019 8:36 am

No issues w.r.t. ground loops if you have VERY solid grounds for both Alternators.

The boys Down und'a, seem to have tripped over the need for DPST Battery cut-off switches.
Cole Hersee PN# 75912 should do you. Dual contacts, each rated at 125A continuous, and
750A intermittent. Might not be a good idea if your running a heavy duty Winch through the
cut-off switch though. I don't know what the rating is for the stock switch, maybe 200A?
As far as I know, no one has reported frying the stock switch with a 24V Winch.

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kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Thu Aug 15, 2019 7:42 pm

The bracket is back from manufacturing!
Image

Super pleased with the results, just need to weld it up and send it for powdercoating.

I decided to run a quick BOM to see how my cost looked versus the +$1000 version from Sweden and I think I'm doing pretty good! Just need to size a V-belt and price it out, but I'm thinking $20 tops.

Image

Really looking forward to wrapping this up so I can start the next project!
1977 Austrian 710M

Tjerk
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Re: Reverse-mount 12V alternator

Post by Tjerk » Fri Aug 16, 2019 4:13 am

Very nice - to think not so long ago they were flame-cut and you still had to grind them.
Add an earth strap to the BOM because you are powder coating the bracket!

kdiqq
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Re: Reverse-mount 12V alternator

Post by kdiqq » Fri Aug 16, 2019 6:53 am

I still deal with flame cut stuff occasionally when we have really thick/large parts. Even then, the cut quality is so nice! Flame cutting has come a long way!

To your note, I plan to run a ground from the back of the alternator to either body or engine. I thought about masking contact areas, but figured that wouldn't be as reliable as I'd like.
1977 Austrian 710M

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