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Old 01-17-2020, 04:44 PM
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Default Pro Point 208 questions (electrical)

Hi all,

I'm modifying snowmobiles for the kids and have purchased and installed Pro Point 208 cc electric start engines. These go on sale and have a cast iron sleeve. They appear to be a great little engine.

https://www.princessauto.com/en/deta...rt/A-p8628257e

I have acquired a bunch of parts from NR Racing treating these engines like a typical 6.5hp clone.

The red sled is a 2000 Polaris XCR 120 the blue sled is a 2018 Polaris Indy 120 that I long tracked. OEM engines are a Roblin 120cc. Both chassis got the Pro Point 208 engine.





here's a quick video of them in action.

https://youtu.be/wqFvc2AXkzY

SOOO

The Problem: I need more charging capacity to charge the battery and run the handle bar warmers. These engines have electric start that works pretty well. They have a charging coil on them that produces about an amp at 13.3 volts DC or so at 3900 RPM. (more volts at higher RPM) The Handle bar warmers and LED lights draw about 2.8 amps. I only get about a day of running the sleds and I need to hook up to a battery charger.

My Solution: Install dual 3 amp charging coils. With the governor removed I am getting about 28V DC. No problem, I'll add a DC-DC regulator.

My Question: I know I need to install a diode coming off the charging coils so that they don't see voltage from the battery. BUT, do I need to isolate each charging coil individually with a diode or can I hook them together and then run one diode? Also, Is it better to hook up the diode AFTER the DC-DC as I assume it will draw power from the battery. My plan is to hook the coils together, have them input to the regulator and then have a diode on the output to stop back feeding from the batteries.



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Old 01-17-2020, 05:37 PM
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I can't help with the electrical stuff, but I just gotta say: Nice sleds!
I wish we had enough snow here in Texas to have snowmobiles!(then I could also swap the engines onto karts)
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Old 01-17-2020, 07:04 PM
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Thanks, the sleds are pretty cool. Kids are 5 and 8 and just LOVE riding them. Stock they are pretty slow but with these engines (and another handful of mods) they really move.

It's nice building engines on the sleds. It's always cold when you run them so... intake always sees cold air, you don't run an air filter as there is no dust, they never over heat, and the clutches are hooked to the track that slip on the snow! It's great!



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Old 01-17-2020, 08:59 PM
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Well usually a single diode is used since the coils are set up in series.
and only have a single wire anyways (being groundend by the engine itself and via their core.

IF by chance you got two wires and no internal protection diodes (continuity both ways).

then you do not want a single diode nor two individual diodes.
What you do want is a rectifier (four diodes)
ideally with a significant heat sink and since you were planning on a DC-DC regulator

instead just buy a rectifier/regulator combo for a motorcycle or a skidoo
(easy to find on amazon ebay or even banggood and such)
that takes care of all your electrical needs then.

skidoo's regulating rectifiers come usually with a four pin connector
(two AC in, two regulated DC out)

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Old 01-17-2020, 09:17 PM
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these are two individual single wire units. Both DC "charging" coils, so no rectifier needed. As apposed to what I would call a "lighting" coil that would have two wires producing AC and would need to go to a rectifier or combo unit as you suggest.

The OEM set up was a single charging coil (DC) going to an external diode. I assume this was only to prevent any current back feeding into the coil via the battery. The OEM flywheel is a 3 pole fly wheel (made for electric start engine) from what I can gather that produces a DC charge through the coils.

My concern is that when adding the second coil, that on every half rotation the opposite coil is sending a charge to the coil that is out of phase, hence needing a diode on each coil????

and maybe after the DC-DC converter as well as to not get a parasitic drain on the battery from the regulator?
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Old 01-17-2020, 10:06 PM
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so if you add two single coils with a single wire each,
you should NOT add them in series.. but in parallel
hence no need for a voltage regulator..
both need individual diodes (to reduce the current per diode)

If however you serialize the coils all you do is double up the voltage.. and well
add a regulator to cut it in half again (which is kinda pointless IMHO)
Also that might be a difficult to get right setup anyways.
since you need to insulate the core of one of the coils. (nylon sleeving isn't always reliable under engine vibration... nylon bolts are too weak for my taste)

So two single coils to me only makes sense in parallel
(I think charging coils have a reverse protection diode build in anyways, no? my cheap gx200 clone has one at least...)
So two diodes out of the box ..

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Old 01-18-2020, 06:40 AM
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Yes, they will be in parallel! I didn't even think of checking them to see if they had a reverse diode for protection built in. Duh. I will do that and see. If not I will add them.

Now to (further) show my ignorance, Isn't the voltage dependent on RPM? At idle (1800rpm) these produce about 7V, with the governor hooked up at WOT (3600rpm) 13.3V and with the governor removed (7000rpm) I am getting about 28V. Hence the need for the regulator??

My tach went on the fritz and I have a new one coming so those RPM aren't completely accurate but I suspect they are close.

Another question, I know that Arc makes a fly wheel with a starter ring gear but it doesn't maintain your charging system. Is there anything else available out there?
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Old 01-18-2020, 10:22 AM
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Yes rpm dependent..
I was expecting you to run those at no more than maybe 4.5k,
since indeed there is no billet flywheel with coil magnets (for very good reason)

and that should give you roughly 16'ish Volts on the coil I think since it's not actually strictly linear..
taking the voltage drop over a reverse protection diode into account (~0.7V)
you'll end up in the 15'ish volts which is still a tolerable voltage to charge your batteries with.
if you get more than that indeed a regulator,
automotive type sealed with heatsink.

Running a stock charging flywheel @7k rpm is asking for trouble (and severe injury)

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Old 01-18-2020, 12:19 PM
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Ok good stuff. Thanks for the help.

Yes, these run around at 3500-5500 rpm 95% of the time, but in deep snow the high RPMs are nice. Lots of "blipping" the throttle on a snowmobile. We are not racing and I understand the concerns of running the stock flywheel at that high of an RPM.

I emailed ARC about adding it to there unit that takes the starter ring but they would not do it. It's too bad as there must be a safe way as my big sled has magnets and it revs to 8250!

As I have never read about or seen a blown flywheel, does anyone just add a thick cage around them to contain the carnage? I'm more worried about the connecting rod blowing (have billet on the way)
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Old 01-18-2020, 12:31 PM
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apples and oranges...

buy a motorcycle or sled engine and you have what you need..
buy an industrial engine and you have to make compromises.

Well you can always make new kids I guess.

No really.. rev limit those engines NOW!!

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Old 01-18-2020, 01:25 PM
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Well, i would actually go for the billet flywheel with ring gear and lose the charging abilities...
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Old 01-18-2020, 11:11 PM
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sure if you want,
but the original flywheels (non charging) are already kinda dangerous at 7k
the ones with charging capabilities are a serious threat..
don't take any chances;
a single bump in the road (well rock beneath the snow) can be enough.
rather not drive the sleds until the billet flywheels are installed.

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Old 01-19-2020, 02:36 PM
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The firewall might help some to keep flying parts from going far, but yeah, it's a good idea to get a billet flywheel to prevent potential injuries from magnets coming off from a flywheel and the flywheel becoming really unbalanced.
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Old 01-20-2020, 03:54 PM
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So quick update:

The charge coils did not have a diode in line so I added a In5404 to each coil. They are rated at 3amps each. I got about 1.1V drop across the diode. No big deal as it's putting out 29V DC at wot under load. I am going to add a 24V relay switched directly from the charge coils to run the hand warmers and lights through the dc-dc. (big silver heat sync box on 4th picture) We'll see if that works.
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Old 01-23-2020, 01:15 PM
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Sooo.... I opened up the engine in the blue Indy today and look what I found. It appears that the ignition coil hit the fly wheel. ouch. Not speed related or installation by me (this engine has not been apart) and still has the gov installed. Or perhaps it was from an over torque situation from the OEM based on the crack being in the key way??





The ign coil had a nick out of it and rub marks on the flywheel



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Old 01-23-2020, 01:28 PM
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That has got to be a casting flaw! Good thing you found that!
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Old 01-23-2020, 05:40 PM
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ya, a bit scary for sure. Had a convo with a buddy. This sled was in a bit of an accident not to long ago. (head on collision) and might have been the catalyst for the failure. Def a faulty part as well.

Good thing I have a billet fly wheel on the shelf. Just no starter ring :-(

Oh and for reference, these 208 Pro Point engines have a 1.180" crankshaft and a .716" wrist pin like the ducar engines.
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