Amps verses volts

[procharger]

My ct has 13.6 volts running but the amps are are over the place

mostly around zero +1 - 1 to -3 or 4  and back up again, new volt

reg. and capacitor  installed same result. Not sure its a problem

but wondering what other people see?

[Al Downs]

Just fixed this problem. Changed the capacitor also check the connections at the shunt,

[procharger]

Thanks what are you calling the shunt?

[Al Downs]

In my 2010 it is behind the panel on the left side. Make sure to check all wires. Double check the connections on the capacitor. I found a bad connection there also.

[Al Downs]

If all of that is done, give Roger a call he is experienced at this problem.

[Roger Lee]

First take off the wires to the shunt behind the EFI's panel on the back firewall. Use some scotch brite on the the terminals and a dab of dielectric grease before you put them back on. There is only one big and one small wire on each end of the shunt. Then if you really want to quiet it down get a much larger capacitor than the 22K one. 22k is the Rotax minimum, but many use something bigger. The 912iS engine has 2 x 33K capacitors.  It should be for 105F for temp rating, but 85F seems to work. It will be considerably larger and will need to be relocated from where the smaller 22K is now behind the engine frame. Doing both of these things will smooth out the amp fluctuations. Just cleaning the wire terminals will make a difference, but not all of it.

[Al Downs]

I will post the capacitor and source that I used when I get to the hangar tomorrow

[Al Downs]

You are one step closer to your next great design!

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[jeffrey]

One issue the cables connection to the battery are very small and come standard, to my understand Rotax state 16mm squared, i have up graded this some time ago. 

[Anticept]

A big, huge help is to check voltage drop with all equipment running except the engine itself.

When doing what I am telling you, you will need to test, write down the numbers, clean, test again. This way you can see if you are doing any improvements. On all power connections that you clean, use emery cloth or a dremel with a wire wheel. Spit shine those connections. You need to apply a thin layer of dielectric grease before reinstalling on the terminals only, don't goop up a bunch of the terminal screws.

DO NOT APPLY DIELECTRIC GREASE TO DATA CARRYING CONDUCTORS.

The procedure:

Set a voltmeter to dc. Start with touching one of the tabs on the ground bus attached to the inside right firewall, and go to battery ground. You want this to be as low as possible. Hundredths of a volt preferred, but no more than a couple tenths. If you see more than that, clean the grounds and try to move any terminals grounding through the starter solenoid case to the same side to see if that brings it down. Lower voltage is better, it means better ground. If cleaning the terminals doesn't seem to work, you may need to crimp on new terminals or replace the wire with a larger gauge. Also, make sure that you sand off some of that anodizing under the bolt head that runs through the firewall and connects to the negative wire, and apply a very thin layer of dielectric.

Next, test from the positive side of the battery to the input side of the ammeter shunt. That should be the left, but not always. The shunt has a very low resistance, the side which reads lower resistance to the battery positive is the input. Same thing, lower is better.

Test from the input side of the shunt to the grounding bus. You will see 12v here. It should be relatively stable, preferably not swinging more than a tenth of a volt (stobes are noisy) but you will have to get a feel for this.

Now test from engine to battery negative, clean and grease those connections too. If necessary, you can add a second grounding wire but it MUST be as large as the installed engine ground. I would prefer people install larger grounds rather than install a second one due to ground loops, but up to you.

Unplug the voltage regulator, inspect for arcing burns or deformities, replace connectors if any found. Spray an electrical contact cleaner and let it set. For extra measure, you can test the charging coil resistance while you have this off if you want, but rotax coils are highly reliable and generally do not fail. Then apply dielectric grease and reconnect.

Take a close look at your capacitor connections. Some are soldered. They should be clean beads. If they look dried out, resolder with extra flux. For push on connections, remove the connections, put your voltmeter on it until it gets close to zero. Switch to ohmmeter mode. You should see the resistance rise over time, this means the cap is working correctly. Use contact cleaner and dielectric grease before reconnecting. The connection should be tight.

Remove the connector on the back of the EMS. Inspect for deformities. Spray with contact cleaner, let set. DO NOT USE DIELECTRIC GREASE. Reinstall.

The EMS picks up its power from wires leading to the input side of the ammeter shunt. This must be done due to how electronic amplifiers work, or they will pick up noise. That connection is fused. If you want to, you can open the inline fuse container and clean it up too, but those arent really exposed to the air.

The last place to consider is the back of the circuit breaker panel. FD really should have used a bus for this, but they chose to use jumper wires which are a pain. You can remove and clean up those terminals too, and check resistance across the circuit breaker with connections removed (should be zero resistance, no more than a few thousanths of an ohm) but this is a lot of effort. I would only do this if I thought there was a problem.

This will clean up your system a lot.

Regardless, rotax engines are very noisy due to the way the regulator rectifier is designed. You're going to see a little ammeter swing from the voltage pulses. A capacitor across the ammeter shunt input to ground might smooth that out but it seems unnecessary.

[FlyingMonkey]

On 1/16/2018 at 11:45 AM, Al Downs said:

You are one step closer to your next great design!

1.800.344.4539

Thank you for placing your order with Digi-Key!   Your order is being processed. You will receive an email confirmation when your order ships.

Order Details   Your salesorder number is 52898376.

Details Availabile Quantity Backorder Quantity Unit Price Extended Price

ALS40A104KF025 399-7543-ND CAP ALUM 100000UF 20% 25V SCREW   Available Quantity Backorder Quantity Unit Price Extended Price   1 0 28.63000 $28.63

1 of 1 parts displayed. View Order History on your ‘My Digi-Key’ account.

Would that cap also work for a 2007 CTSW?  I have been thinking of upgrading.

[Al Downs]

I think so. A larger one will smooth out the readings better than a small one.

[Roger Lee]

The 22k capacitor is the minimum recommended by Rotax. You absolutely can go larger in capacity. This usually means larger in size to.