Subject: UtterPower.com Contact Form: ST Gen/ Light Flicker
From: David J.
ST Gen/ Light Flicker
I have a ST gen head from Tom at CGG and the harmonic winding wasn’t enough to maintain excitation voltage on the machine. Tom sent me a 120VAC AVR and instructed me to use one half of the machine output to provide excitation for the unit. The problem is that the 120VAC leg that is not providing the excitation is rock solid at 62 Hz no load and the one feeding the AVR is all over the place and causing the lighting on that half to flicker or pulse. Can you suggest a different way or a solution to provide excitation for my ST gen head? I am running the gen head with a Yanmar @2800 rpm and using a Fluke meter to measure the voltage and frequency for each 120VAC leg. Thanks, David J.
This is an excellent question, and it can lead to a lot of learning.
We really need analyze the windings, and what they are doing, and since our rotating machine is designed to run at 60HZ, that’s where I choose to take measurements after we do the basic checks.
I believe in Kiss, and I do think it’s best to evaluate what you have in steps. On new heads we always document these readings and keep them, or we risk paying the price later. This way you know what you had when it worked right, and you can do a compare later if you do have trouble.
Step one, a good meter is a must, if you don’t have a good meter, borrow one. (a Fluke is a good meter).
Read and record the resistance value of all windings. Harmonic, Stators, and Field.
- Consult your drawings and specs, are they in spec?
- Don’t do anything to risk your warranty, check with your vendor before you conduct any further tests.
- Most STs are designed to function with a standard rectifier, consider checking with your vendor, the radio Shack 30 amp rectifier they’ve had in stock for 30 years is normally plenty, the PIV rating need be well above the voltage peaks.
With the rectifier AC side wired to the harmonic, and the DC side to the field, apply 12 volts from a battery across the DC side (flash the field) with the same polarity as marked on the DC side of the rectifier.. Check all brushes and wiring, (this is very important, if you are a regular visitor you’d note that poor connections in brush wires can cause weird behavior).
If the harmonic winding and the field winding are NOT working as specified on the name plate, (voltage and current) at 60HZ, then you likely have a problem with the Gen Head. Do you need to know more? Is it in your best interest to apply a Band-Aid to mask the problem?
As for using one of the stator windings (120VAC) to power the ST field, I Haven’t seen that, so I’d greatly appreciate others commenting if they have that setup, and they are happy with it? I know that the people I have talked to think Tom works hard to make things right with customers, so I am not critical of his approach to help solve your problem.
If you are on grid you might try using another source of 120vac to drive this AVR just to see how it works… and if you have a link to drawings or other info, sharing with other DIYers here would be great.
The flicker issue: Since I don’t know about the circuit, hard for me to comment. My approach would be to put it on the other stator winding and see how it works over there.
I would think if one stator is flicker free with a load, then the field itself is not the source of the problem, that would suggest a need to examine what’s going on current and voltage wise in the one stator that’s being use to drive the field, and most would want to look at both current and voltage in that stator, and display the output on a scope. There are very inexpensive scopes you can use with a lap top, a data analyzer would be great.
Others, keep me honest here.. I have little use for the Chinese AVR, I’d rather live with an acceptable voltage droop for most of what I do, as making power is far more important than keeping the voltage tighter than I require. Adding parts and complexity is fine if it meets your needs, but IF you are wanting a generator to make power in an outage, the kiss back up is a very nice option, no juice? Fall back to KISS designs..
As always, I suggest that people check every connection on the STs, and I personally eliminate the dog house and most of the crap supplied. The better connection is a properly sized twist nut, with tape over that, the volt meter needs to be off the set if you are wiring it up stationary. Big singles punish meter movements over time.
We all need Identify our goals when we build our generators. High on my priority list is a very quick fix IF I have trouble.
If you think the AVR is a must, then it’s best that you write down exactly why, and we do need know that AVRs can be very simple devices, and some quite complex and costing more than many generators. One thing we want to be sure of, and that is that the AVR is designed specifically for your gen head, OR it has an adjustment to limit the current in the field to assure it’s not over driven and damaged. And if it does have that adjustment, that you set it.. otherwise, consider a fuse in the field supply to assure it’s not damaged.
A great place to learn about simple AVRs is in Electrical repair shops where people contract to take care of assets from large to small for a construction company for instance. They know of the complaint in small portable generators.. “The guy said it was working fine till it ran out of fuel.” In this case, a bare bones AVR can attempt to boost current as the generator slows down to the point where something in the field circuit fails, a marginal brush, poor connection, or it might just smoke the field if the AVR and field are not properly designed to dance together.