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Onan Cummins 35kw conversion to 480V from 208V

w-cummins

Registered
Stupid question...

What powers these transfer switches? Power off, gen off, caps in the power sentry? starting battery??

William....
 

Zephyr7

Registered
Stupid question...

What powers these transfer switches? Power off, gen off, caps in the power sentry? starting battery??

William....
The generator powers them. The usual sequence for a “normal” ATS is like this:

1 - normal source (utility) powers everything
2 - normal source fails, ATS controls lose power
- time delay starts (May be a mechanical timer or a small battery powered timer)
- time delay ends, start relay contacts close
3 - generator starts. Generator starter, controller, and the control circuit through the start contacts in the ATS are all powered by the generators starting battery
4 - generator power re-energizes ATS controls
5 - ATS closes on emergency source using emergency source (generator) power to run the actuator

When the normal source is reenergized, the cycle goes in reverse but with a “qualifying” timer that makes sure the normal source is really ok before switching back to it. A cooldown timer keeps the generator running at least a few minutes before opening the generator start/run control circuit to shut the generator down.

The ATS control logic is designed such that it fails sending a start signal to the generator (start/run relay contacts closed). This way if normal fails and the generator doesn’t start, as soon as the generator is fixed everything still works and the ATS will switch to emergency regardless of how long it didn’t have power.

Bill
 
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w-cummins

Registered
The generator powers them. The usually sequence for a “normal” ATS is like this:

1 - normal source (utility) powers everything
2 - normal source fails, ATS controls lose power


- time delay starts (May be a mechanical timer or a small battery powered timer)
- time delay ends, start relay contacts close
So the contactor/switch remains connected to the utility power at this point? In the case of the Cummins switch there appears not to be a battery (at least I didn't see one in the parts list) so... what happens if the gen doesn't start? It just powers out and sits there??

So the ATS can see power on either side and power its self from either side and by passes the large switching contactor? Is there a mechanical interlock that prevents cross connecting the sources?



The ATS control logic is designed such that it fails sending a start signal to the generator (start/run relay contacts closed). This way if normal fails and the generator doesn’t start, as soon as the generator is fixed everything still works and the ATS will switch to emergency regardless of how long it didn’t have power.

Normally closed relay?
I thought that if it had an over crank it locked out the starting?

William..
 

Billy J Shafer

Subscriber
Age
69
Last Subscription Date
09/03/2019
Power sentry from an OT no. Power sentry from the OT III. You would have to swap the whole control system. Probably be cheaper to find a complete switch.
 

Zephyr7

Registered
So the contactor/switch remains connected to the utility power at this point? In the case of the Cummins switch there appears not to be a battery (at least I didn't see one in the parts list) so... what happens if the gen doesn't start? It just powers out and sits there??
If the generator fails to start, the ATS just sits there with the start contacts closed. There is no power to make the ATS transfer, but there’s no other source to transfer to anyway without the generator running.

So the ATS can see power on either side and power its self from either side and by passes the large switching contactor? Is there a mechanical interlock that prevents cross connecting the sources?
Yes and yes. The ATS can be powered from either source, and often is interlocked so that the power to transfer to a source comes from the source that will be transferred to.

Usually an ATS is only mechanically capable of connecting to one source at a time (one metal piece that switches to contacts from one source or the other). Some of the older switches had different switch mechanisms for each source, but a mechanically interlocked actuator system so they couldn’t both be connected at the same time.

Normally closed relay?
I thought that if it had an over crank it locked out the starting?
Yes, usually the generator start signal comes from a normally closed relay in the ATS.

Overcrank protection and lockout is handled by the generator controller, not the ATS. A typical ATS is pretty dumb and doesn’t talk to the generator except for sending a “start/run” signal. The ATS signals the generator to start by opening that start/run contact. That is the usual “two wire start” system.

There was a three wire start too, but it’s much less common than the two wire system.

Bill
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
Generator start is through a normally OPEN set of contacts that CLOSE to signal the generator to start. You can put that N.O. switch anywhere you want, and parallel a bunch of them to enable starting from multiple locations, if desired, even without a transfer switch. From the OTC manual - Although the logic is more involved, the two-wire starting circuit can be thought of as a single pole, single throw switch. A closed switch signals the generator set to start. An open switch signals the electric generator set to stop. zuhnc
 

Zephyr7

Registered
Correct, start signal is a CLOSED set of contacts. But the relay itself is NOT normally open. “Normally open” refers to the state the contacts would be in while the relay is NOT enegized. Since the relay in an ATS keeps the contacts open while its energized (because it needs to close to signal a start, and it needs to do that when the power fails), the relay itself has to have normally closed contacts.

The relay in the ATS is energized while the normal source is present, and closes when the normal source fails. This means the relay itself has a set of normally closed contacts that are held open while it’s energized. Normally closed relay, but a normally open control circuit (the open condition is the generator NOT running).

It’s all a matter of perspective, and how the terms are defined.

Bill
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
Correct; we are on the same page! Onan always shows their components on the schematics in the "de-energized" state, which is confusing to some. I find it easier to trace out operating paths on such a schematic. zuhnc
 

w-cummins

Registered
Ok thread back from the dead.....

I finally got the gen set "home" don't ask.....

Anyway

The transfer switch seems to be an automatic version, I'm wondering if they just had a non-automatic version on hand and converted it to automatic operation as it appears to have all the needed stuff to run that way. Here are some pictures of the switch.

Thanks

William....
 

Attachments

Zephyr7

Registered
I’ve seen ATSes setup to be operate manually with push buttons before, but it’s unusual. Most people want the “Auto” part.

Yours certainly does look like it has all the stuff to be an auto unit. The boards on the right with all the pots look similar to an older Asco unit I worked on at one of my sites. The pots adjust many things (most silscreened on the boards), and it does everything with analog logic. The downside is aging capacitors can cause some weird things to happen. In the one I worked on, it wouldn’t go back to normal after transferring to generator. I had to do some component replacement to fix it.

Bill
 

w-cummins

Registered
Well I hope that the unit works as it was removed from a working install. But as we all know, nothing is a sure deal. It appears that you can probably make the existing control cards into more "full featured" models by adding the missing components to the boards. Also there are not many caps if I should need to re-cap them.

William....
 

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Zephyr7

Registered
You only need to replace electrolytic caps due to age. The yellow drop-like ones (tantalums) and the boxy type (usually film caps) don’t really age.

I wouldn’t try adding missing parts. You won’t know what they’re for, and sometimes the other parts are there for a different design revision. Something like “use ICs 1, 2 and 3, or use only IC 4, depending of if it’s cheaper to buy 1, 2 and 3 instead of just 4”. It’s not uncommon to design things that way so they have different component sourcing options during production without needed to do a redesign (known as a “respin” when doing a board layout).

Bill
 

EricWood

Subscriber
Last Subscription Date
10/15/2019
Agree with Bill—I wouldn’t entertain the idea of filling the board out, without the engineering drawing.

That board is the standard A option undervoltage card. Same card used in utility and generator positions.

All the extra space, is when the optional B option card is made, which includes overvoltage and underfrequency additions.
 

w-cummins

Registered
Yep I know that only the electrolytic caps dry out, there are only 3 on each of the cards, and 3 more on the MB if I need to recap the whole deal!

I'm not going to repopulate the cards for the added function as I really don't think I need the over voltage I guess the frequency would be nice for the gen side, at least on my end the utility side is rock stable for the frequency regulation.

I'm setting up the switch and was wondering if some on had a link to the OTIII service manual I have the instillation manuals for the gen and switch but neither of the service manuals.

Looks like I only need to change the battery charger transformer, and the 2 24v control transformers to operate on 480V and then come up with the "Fix" for the linear motor.

I'm thinking that a single 480-240V control transformer will run it just fine as it's single phase 208/240v and is rated at 1900w.

If I put the control transformer in front of the cap/motor and connect it to the sentinel board it shouldn't have too bad of a delay as it energizes the transformer and charges the cap up??

Thanks

William....
 

EricWood

Subscriber
Last Subscription Date
10/15/2019
....Looks like I only need to change the battery charger transformer, and the 2 24v control transformers to operate on 480V and then come up with the "Fix" for the linear motor....
You’ll need to re-configure those four sensing transformer leads and jumpers below the motherboard module as well per service manual diagram. And recalibrate the voltage sensing cards.

Your manual:
http://www.skilledcrafting.com/onan... Transfer Switch Service manual (06-2001).pdf
 

w-cummins

Registered
You’ll need to re-configure those four sensing transformer leads and jumpers below the motherboard module as well per service manual diagram. And recalibrate the voltage sensing cards.

Thanks for the manual link!

only problem is the more you learn the more you find out how little you know:(

So after reading the manual I now have more questions

looks like Cummins/Onan is doing what I was thinking about doing with the 600V switch

running a lower voltage motor with an additional transformer and a set of interlocked K1 and K2 contactors in place of the normal relays.

Has anyone seen one of these setups??

Also I have been looking at other switches to get the required parts to convert mine to 480, looks like it may be cheaper than the conversion kit if I change the motor out.
It appears that the switching parts of the 40,70, and 125 amp switches are the same with just a different cover labels. Is that true ( the parts manuals don't seem to show different part numbers for them)??

Thanks

William.....
 

w-cummins

Registered
Ok I think I now have a solution to convert my switch!

I looked at MANY pictures of 70 and 125 amp switches and was able to get the part numbers of the motor with 480 coils

I then found some one selling one (a member of this board!) and he also had the caps and the circuit breaker too, as he converted his switch from 480 to 240!

What I don't have is the instruction sheet for the install, and the wiring diagram.

Another question also is causing me confusion! The caps are only rated 330V and the circuit breaker is only 250V seems that that could be a problem for operation at 480V. ??

I have seen pictures of the switch setup for 480V operation and it too has the 2 330V caps. I can't confirm the CB though as you can't see the back of it in any pictures as its hidden and that's where the voltage rating is listed on the part, However the company that makes that style of CB dose not make any higher rated units.

Any one know if these parts are the correct and how they can operate @480v ??

Thanks

William...
 

Zephyr7

Registered
Breaker is probably an issue, caps maybe, but maybe not.

480v is 277v to ground in a wye, so caps might be ok. Caps might also be in a series string. If the 480v switch from the factory uses the same 330v caps then it should be ok and I wouldn’t worry about it.

480v breakers should have higher than 250v ratings. It would be strange to see a factory 480v gizmo with a breaker not rated for 480v.

Bill
 

w-cummins

Registered
480v is 277v to ground in a wye, so caps might be ok.
Right but this motor is 480V not 277V and the switch dose not appear to use the grounded conductor at all.

Caps might also be in a series string.
I'm thinking that this is probably the case. I don't have the wire diagram yet for the 480V switch. The parts came with one jumper wire that I'm assuming is used to connect the "string"

If the 480v switch from the factory uses the same 330v caps then it should be ok and I wouldn’t worry about it.
Yep I'm thinking it's fine too. The series connection would 1/2x the voltage each cap would "see"

480v breakers should have higher than 250v ratings. It would be strange to see a factory 480v gizmo with a breaker not rated for 480v.

Bill
It looks like that the breaker also sits in the above circuit if so it may also be "ok"

I need to get the wire diagram called out in the sheets that came with the switch

626-1690 (D)

it has the connection for the 2nd cap listed...
I think I know how to hook it up, but I really would have my thoughts checked with the official document rather than let out the magic smoke!!

I called the local Cummins dist. But they said that they didn't have access to the tech drawings.

looks like the "conversion kit" might also have a useful document

C275b


Thanks

William.....
 

Attachments

Zephyr7

Registered
If the generator end is wired as a wye, then you still have 277v to ground on each phase, even if you’re only taking the 480v delta connection out of the box.

If you have the unit wired for 480v delta (I STRONGLY advise against doing this unless you have no choice, the wye connection has many advantages even if you are only supplying delta loads), then you need a 480v delta-rated breaker. Such a breaker will be rated for at least 480v PER POLE, so any pole is rated to break at least 480v on its own. Most common breakers are only rated to break 480v in a phase-to-phase connection where two poles are in series.

Bill
 
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