This might be a dumb question, but I have asked the "Experts" at my home airport and got different answers. I believe that the Chevrons point to the positive side. But some say no negative. Any comments
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This might be a dumb question, but I have asked the "Experts" at my home airport and got different answers. I believe that the Chevrons point to the positive side. But some say no negative. Any comments
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agfox,
This is one of those things you need to sure of in your own head....a person ends up buying more parts if it is connected the wrong way.
Here is one reference on the subject of capacitor polarity ID.
http://denethor.wlu.ca/common/capacitor_polarity.pdf
Not saying I am an electrical engineer...however after studying the subject during my build I found that capacitors are generally marked (confusingly) in two ways. The logical one uses a "+" by the terminal which is supposed to be connected to the positive side of the system. The illogical one identifies the negative terminal which is suposed to be connected to negative side of the system with either an arrow or a series of chevrons pointing to the negative terminal up the side of the capacitor.
FWIW - I connected the terminal with the chevrons pointing to it to the negative side of the system - been running flawlessly for 300 hours - no smoke or fires.
To make it really confusing - some capacitors can be hooked up either way - the one used on Rotax Charging system is an electrolytic capacitor which has ony one right way.
It's a variable marking system designed to confuse a person - so it's not a dumb question - it's a smart question - be sure you have it correct - one way it will work, the other way you will end up burning up some expensive parts.
Sincerely,
As Dave surmised, polarity bar (Chevron stripe) is negative. Tie it to ground and you should be good to go.
Thanks Guys. Don't ask me how I know but if you connect wrong you get a loud bang, smoke, and oil dripping out of the thing.
...and it stinks like crazy too.Quote:
Originally Posted by Agfoxflyer
Wired it up. Flipped switches. No pop, smoke, oil, or smell. Good to go!
What are they used for on a Kitfox?
In our charging systems, the stator produces AC output which goes to the regulator/rectifier. The ouput of that is DC plus an AC voltage on top of it. A capacitor is often used to filter out higher frequency AC ripple on the rectified DC supply. It helps keep the electronics happy and audio quiet.
Thanks, I was thinking to myself, there really cant be much on a kitfox that pulls enough power on start up that you to need the extra stored power of a capacitor but if it acts as a filter too that makes more sense.Quote:
Originally Posted by Av8r_Sed
So how do you wire these things up, Do you run the hot wire to the positive side then continue from the positive side to the electronics buss? And ground side to ground, or does power go in one side and come out the other?
They go the first way you described, in parallel across the power and ground. If you wired it in series, all you'd get out of it would be AC and none of your electronics would work.
Is there are preferred "connector" or "terminal" that one uses to connect the wires to these two little metal tabs sticking out of it's top?
Excellent thread! Thank you!
I believe those small metal tabs are for a soldered connection. Don't they have a small hole in them to attach the wire before soldering?
Jim, there are NO holes on the ends. They are just very skinny; just two tabs sticking out of the capacitor. The tab ends are pointed and slightly turned.... weird!
Grover,
Do you have a picture and/or a manufacturer and part number for your cap?
Edit, if it's the same cap that's pictured earlier in the thread, it's designed to be soldered into a PC board. No reason you can't solder wire to thos tabs, but I personally like the screw terminal type in this application. You're also more likely to fin mounting hardware for them.
Hi Grover,
I got the same type capacitor in my kit, and I believe those are solder tabs. I decided I really wanted to have screw terminals so I got a really nice one with screws and a higher voltage rating also (50 v.). Not trying to encourage anyone else to do that (spend more money when you have a perfectly good part to begin with), but that's what I did.
John, where did you get your new capacitor? I want screw terminals as well.
Hi Josh,Quote:
Originally Posted by Esser
I bought it online from Digi-Key -
https://www.digikey.com/products/en?...ds=493-8948-ND
Thanks John. Interestingly, the Rotax manual recommends 22000uF for the 40A alternator too.
I found out that Silent Hektik recommends even higher ... 33,000 uf? My capacitor is “beefier” than the original at a 50v rating, but still 22,000 uf. There may be some potential benefit to a higher micro farad rating, with no real downside. It’s still unclear to me what the capacitor actually does in this circuit. I’ve read some descriptions of that which are obviously incorrect. When I take the time to find out for sure I’ll post it on this forum. Of course there are people participating here who can probably tell all of us the real facts already.
I’m sure you’ve noticed with all my questions I’m new at this stuff. Apparently from what I gather it’s mostly there to take out alternator noise. It makes me wonder if I really need two capacitors for two alternators...
Josh,
FWIW - I am running both alternators (Not fuel injected - just two alternators on two separate systems with a cross tie) and do not have a separate cap for the belt drive alternator - no problem with alternator noise.
Good to know Dave, just interested to hear why you went with no capacitor an the external alt when Rotax recommends it? Did you know of other people having success too? I may go this route...
Josh,
I don't recall seeing any requirement for a capacitor on the belt drive alternator at the time I bought the unit.
Also remember that this was quite a few years ago (2006 or there abouts) and I believe the EFI rotax engine was still a gleam in the eye of some Rotax engineer - I do not have an EFI or turbo engine - just the garden variety ULS with a need for more juice than the little integral alternator could provide.
My electrical system has two separate busses/batteries/alternators with a cross tie if one or the other fails. All my essential stuff including radios is on the integral alternator and all the high draw stuff like position lights and strobes, etc is on the belt drive alternator.
Just a wild elbow guess; but, I wonder if the cap for the belt drive alternator was added at a later date????? Maybe there is now a reason for it?
Not aware of anyone else with this setup.
It’s on page 47 of my 914 installation manual. I’ll poke around. I don’t know why one couldn’t do the job for both if it wasn’t a competely separate system
This is kind of an older post, I found it when I was looking for some info on the 912 wireing. A while back I picked up a 912 engine that had some ignition problems. I'm building a stand where I can run the engine and sort out the ignition issues before I get around to mounting it on the plane that I'm rebuilding. Also, I want to get it running and sorted out before it gets to cold up here in Mn. With having to build the panel and other things on the plane, if I wait till that's done, it will be well into winter, (maybe next summer :-) I guess my question is: should I worry about having a capacitor wired in for what I'm trying to do at this point? Or does the capacitor mainly filter out noise in the system, but doesn't really effect the charging system? Basicly, I don't want to burn out the alternator or regulator. Thanks, JImChukQuote:
Originally Posted by jrevens
I was digging through the installation manual today, and it had a circle around the capacitor and it said optional. So I guess I should be able to run the engine for a little bit with out it. JImChuk
Do you need a charging system for an engine on a test stand? The ignition system should be independent of the charging system. Might simplify things a little unless you’re trying to test the charging system as well.
I'm not sure. Would it hurt the alternator to be producing power if it can't go anywhere? I had just figured to temporarily wire things up and run it so I could tell if things were sorted out with the ignition or what ever it took to get it there. The last thing I am is an electrician.... :-) Any help is appreciated. JImChuk
Shouldn’t be a problem to leave unwired, but I’ve never done it myself.
Probably not that hard to run a few temp. wires to the regulator and such. If I cooked the stator or something, I would wish I had. But I don't know if it's needed or not. JImChuk
I understand. Just make sure to meet any minimum load requirements if the regulator requires it.
Neither Model IV 96KL or 338S had or has the capacitor or has shown a noise problem. 900 hours on the first one.Quote:
Originally Posted by avidflyer
Bob Nuckolls (AeroElectric Connection) has stated:
"As long as you have a battery on line,
the capacitor serves no demonstrable
purpose."
It's actual intended purpose seems to be a mystery to many owners, but I do not believe that it is there as a noise filter as many seem to think. I tend to generally believe and accept what Bob says, and it seems like Lowell's experience probably tends to confirm his statement. I'm guessing that the capacitor provides some kind of a buffer if the battery is disconnected, preventing unwanted bad things from happening? :confused:
Thanks guys for the info. JImChuk
I bought the capacitor for my Rotax 912UI because I heard that if I use an EarthX battery, I will want the "cleaner" power supplied to the charging system. Im so gullible. Although, my source is a demigod in the Kitfox community.
Dare I say his name? nope.