Today I received and interesting email about an ST head that would not self excite.
From: Rick S.
Subject: ST Head
Message Body:
Hi George,
I bought your Utterpower Cd a few years ago and had trouble free running a Lister with the ST head, But now I have a problem with the head not self exciting.
If I use the battery method to reflash all is ok and generator works perfectly no problems at all, but if I stop and restart the generator It produces no current until its reflashed again.
Whatever is happening its not holding any residual magnetism at all.
Have you ever had this problem before?
All ohm readings at the beginning are still the same today so I know all is ok apart from the problem I mentioned.
Look forward to your reply
Best Regards
Rick
Rick,
Great topic! As you know, the ST head works exactly like so many hardware store generators, the source of field power comes from the harmonic winding in the stator, and is then routed to the rectifier to be rectified to DC and then onto the field via the brushes.
For the sake of others who follow, the generator normally holds some residual magnetism, and will start on it’s own. when it doesn’t there may be a combination of troubles, and there’s a reason to check things out..
I never trust the factory wiring, I check every brush lead, and every connection, I don;t trust the chinese rectifier, and I replace them with a western 30 amp unit with a 1000 volt PIV rating.. way overkill, but it’s what I do.
the battery flash may be temporarily healing a bad connection.. check them all, and do put as much load on the generator as it will carry and leave it there for a bit.. check the field voltage against the name plate and report back.. please..
This is a simple system, and it will be a simple problem.. when you bring the generator upto speed, take an AC reading at the AC side of the rectifier..
George B.
Hi George,
I have checked and double checked the wiring, and found nothing at all.
The one thing that is strange to me is that it states on the name plate that the excite voltage is 49v, when the head is flashed and starts to produce the voltage is 29 vac Z1-Z2 and the field is 25 vdc?
This head is a 230 v 50 hz unit. (actually today produced 242v @50hz)
Also I have run a 3kw load for 30mins then shut down, restarted and nothing so no residual magnetism.
The head will also produce when a light load is put onto it like an electric drill and pull the trigger.
I don’t know what to do next regarding it not self starting.
Rick
Rick, this is an interesting topic, sounds like you have done your homework but.. we go over it for others, and I hope others will share their experience to help make this post more valuable.. As I have said over the years, there can be a lot of differences in Chinese ST heads from one shipment to the next EVEN in the same brands! So I write from the position I haven’t seen it all. I was just talking to Wally Johnson near Snowflake, he has a 49 Dodge power wagon that needs the generator ‘flashed’ after sitting a week, and he says it’s wired right with good connections.
Oh.. I feel a rant coming on! The professional can resist such things.. I can’t…..
As per your voltage stated on the name plate, and what you measure, I’d expect it to be much closer.. and I would lift one side off the input of the rectifier and measure it then. the name plate field voltage should be in DC voltage right? If we measure at the input of the rectifier, we are looking at AC, and most meters are set to measure RMS right.. On the DC side of the rectifier, we expect to see closer to a peak voltage. Perhaps we have a reader with a similar 50HZ head that can verify what they see, and share the results?
A typical ST head can sit unmolested all winter and start with residual magnetism no problem.. (my experience). We can’t assume the electrical lams are even the same batch to batch.. and I have seen ST5 heads with the same build spec with a difference of more than 20 volts on the name plate! One manufacturer making a generator requiring more field power to carry full rated load.
When I saw a difference of 40 pounds in ST5 heads WITH the same build spec, I lost confidence in my ability to order these heads with any certainty I would receive. At this point, I’m not sure the generator manufacturer knows what he’s assembling either. 40 pounds is a lot of material to add or delete in one generator, and having far different field voltages, and declaring the build under the same spec does not build confidence at the consumer end.. do we attempt to compare apples and oranges all with the ST label?
Others have moved on, they now buy Chinese made generators with different model numbers, and of course we DIYers will ask.. just what assurances do we have that the one we received is the same as the one we saw across town?
How many DIYers bitch about planned obsolesence? About taking a perfectly good design and Dis- continuing it for some unknown purpose?
If thrity of our kind got together, we’d likely agree on our marketing strategy. We might call our generator Company RTR-Inc ‘Real Time Reliable’, and we’d advertise, that nothing had changed in our design since 1958.. other than superior insulation materials, and more reliable and durable paints and finishes.
Hi George,
Just a quick update on the ST head.
When I first installed it many years ago I did as you suggested on your CD and made notes of all electrical measurements etc, as you also said to replace all the chinese wiring regarding the brush rigging so this I also did and have had many years of not even touching it.
As my last response I had checked all wiring and resistances and was absolutely convinced all was correct. Now after reading your earlier response again It made me think , as you quoted.. This is a simple system, and it will be a simple problem.. So I got my notes out once again and started though 1 by 1 , I had previously made a note that I took the field reading across the slip rings when first installed and that’s what I did this time.. all correct. That’s when the penny dropped thinking of your quote ..something simple. I tried a different way this time and pulled the dc side from the rectifier and measured.. BINGO twice the resistance.
On further investigation I had noticed that the brushes where the only items left from the original chinese wiring and I had forgot to solder the eyes onto the brush leads, as from China they are only crimped. Over the years there must have been slight corrosion building up between the copper wire and eye, so I re soldered the eyes and refitted.
I didn’t even re flash the Gen, Just give the Lister a swing and once the head got up to speed I only waited maybe 5 seconds and guess what.. It started on its own.
So a big thanks to you George for sorting this out.. It wasn’t me.. I’m just a general dogs body. So If anybody else has a similar problem well here is the answer.. Quoted from George.. This is a simple system, and it will be a simple problem. How right you were.
Cheers all the best
Rick
Rick,
It’s an excellent move you made.. recording the resistances WHEN you started, and knowing what it looked like when all was good!
Someweree I wrote an article about boat builders that build boats that start easily for about five years.. the wire between the ignition and aft where the starter soleniod is can be 20 feet long, and over the years it corrodes and resistance increases.. it’s such a common problem that many marine shops hand customers who complain of the no start condition a relay half way through the description of the problem!
In this case, the ST brushes and the lack of soldering is a common problem, hats off to you for recording those readings, and for actually looking at those connections. A lot of people would waste another week hoping the good fairy would fix it for them. Thanks for your contribution here.
GB
Hi George,
Just another question, thought you might know.
The ST5 on a Lister 6:1 when its making 240v its running at 650rpm give and take a few, so when its running a 3 kw load its starting to drop to 230 ish. Now I know a 6hp engine won’t get to 5kw, but what I cant understand is why the voltage is starting to drop at 3kw. If I look at the rack it has still got 1/4in to go to the stop and if I open the rack manually the engine revs stronger and can easily reach 240v again with room to spare. So Im thinking a stronger spring will achieve this, but on the other hand this will be no good because the no load speed will be higher as the stronger spring will be opening the rack further.
Have you had one else make comment to regarding this, if so is there a work around?
Cheers
Rick
This is a govenor issue the droop doesn’t sound all that bad really.
A lot of us run slightly high (voltage/frequency) at no load, so we can split the difference at the lower end..