110 Electrical Guru needed

Sean · June 03, 2009, 01:18:33 PM

Quote from: bobofthenorth on June 03, 2009, 01:08:17 PM
The circuitry I have already has a delay built in. I have never timed it but its likely 15 or 20 seconds. Long enough that I can walk around the bus and hear the transfer switch click in. My intent is to manually delay the existing delay so that I can control the warm up time for the Kubota.

OK, but if you intend to use the existing delay circuit and just change from the existing DPDT relay to a three-pole contactor, you will need to first find out what voltage the delay circuit puts out.

While it might be common sense to think it is 120VAC, it is actually fairly common that the control signal ends up being DC (due to the way the delay electronics work). So the coil on your existing relay might be 110VDC, rather than 120VAC. It ought to be marked on the relay itself, but, if not, get your voltmeter out and measure at the coil terminals.

If you do have a 110VDC coil, that will complicate the contactor installation. You will either need to change one of the contactor coils, so that one is 120VAC and the other 110VDC, or you will have to rectify the shore power sense lead to 110VDC and get a contactor with two 110VDC coils.

Did that make sense?

-Sean
http://ourodyssey.blogspot.com

Sean · June 03, 2009, 01:29:06 PM

Sorry, one further note, about "priority":

The switch you have now could be considered to be "generator priority," which is to say that, even if shore is connected and hot, when the generator comes on-line, the switch will transfer the load to the generator, and the shore will be idle.

With an interlocking contactor, the priority is FCFS -- if both sources are hot, the load will be connected to whichever source was hot first. So if shore is hot and connected, merely starting the generator will not cause the load to transfer.

This can be fixed by running the shore sense lead through another NC relay, energized by the generator, so the shore contactor will be interupted on genny start-up.

One way to accomplish this cheaply, which would also solve any incompatible voltage issues with the existing delay circuit, is to use the existing DPDT transfer relay as a "control" relay. One pole, operating in the NC mode, would be used to interrupt the shore sense, to open the shore contactor, and the other pole would be used in the NO mode to provide standard 120VAC operating current to the generator contactor. The downside, of course, is now you have to find room not only for the three-phase motor starter (which is, itself, much larger than what you already have), but also for the existing relay. Probably a tight fit in your existing enclosure.

This might be another factor which drives you to just change out the whole unit for one that already does what you want. FWIW.

-Sean
http://ourodyssey.blogspot.com

bobofthenorth · June 03, 2009, 01:59:27 PM

OK - I got in there with a magnifying glass looking for a voltage on the coil and discovered a part number on the switch or maybe 'relay' is the right word. It is a Deltrol Controls 900Q DPDT 20791-84. 110VDC coil, 1.5HP or 30 amp @ 120/240 contacts.

Before this project gets runaway complicated, wouldn't this relay work off my existing delay circuitry? I'm quite prepared to manage the generator and I don't think I want it to be starting up on its own. The goal of this project is only to remove the generator neutral bond while I'm on shore power.

Sean · June 03, 2009, 02:07:43 PM

Bob,

If you have a 50-amp shore setup, the relay you linked is too small -- contacts rated only at 30 amps.

Of course, it seems the one you have in there now is also only rated at 30 amps. Which itself is a problem if you have a 50-amp system.

-Sean
http://ourodyssey.blogspot.com

Len Silva · June 03, 2009, 02:10:13 PM

Bob,
If you are careful managing your power use, that is not turning on any major loads until the generator is up to speed, you can get away without the delay. The air conditioner(s) probably have their own built in delay. You still need a relay or auxiliary contact (available on most reversing contactors) to establish generator priority.

Sean · June 03, 2009, 02:14:07 PM

Hey, look what I found. Once you posted the part number for the relay, I found the manual for your transfer switch:
www.escousa.net/Merchant2/graphics/00000001/LPT30TrblShootRepair020206.pdf

Looks to be an ESCO model LPT30, which is a 30-amp, 120-volt (only) RV transfer switch. So in addition to poor wiring practices, looks like they also forced a 120-volt ATS into a 120/240-volt application (which is why you now have the neutral problem), and too small to boot.

Again, if you have a 50-amp, 120/240 system, I recommend you replace this with an ATS of the proper rating.

The more I think about this, the more I wonder if Bruce didn't wire the coach properly, and then "Doofus" modified this switch when he put the genny in?

-Sean
http://ourodyssey.blogspot.com

Sean · June 03, 2009, 02:17:52 PM

Quote from: Len Silva on June 03, 2009, 02:10:13 PM
... You still need a relay or auxiliary contact (available on most reversing contactors) to establish generator priority.

Len, the aux. contacts on the reversing starter itself, while sufficient to keep things safe by not allowing the opposite contactor to energize, will not by themselves allow you to establish priority. Once the shore contactor is energized, there is no way for the generator contactor to open its NC aux. contacts (and vice-versa). You absolutely need another relay.

-Sean
http://ourodyssey.blogspot.com

Len Silva · June 04, 2009, 08:12:17 AM

Well Sean, it looks like the commercially available units are actually "Shore power priority". This is what I have in my MH, a Todd Engineering PS-250. The Lyght and ESCO units are identical.

http://www.generatorjoe.net/html/esco/LPT50CA.pdf
http://www.escousa.net/Merchant2/graphics/00000001/LPT50CATrblShootRepair091906.pdf

The ESCO LPT50CA mentions a "Shoreline Release Switch, 120 VAC, N.C." which I guess is to force it to switch to generator even when shore power is available.

Len

Sean · June 04, 2009, 08:25:52 AM

Quote from: Len Silva on June 04, 2009, 08:12:17 AM
.. a "Shoreline Release Switch, 120 VAC, N.C." which I guess is to force it to switch to generator even when shore power is available.

Right... that would simply interrupt the coil voltage on the shore contactor long enough for the genny contactor to close. To implement generator priority, I would propose a 120VAC, NC relay to do the same thing, energized from the generator.

I have a similar setup, only, in my case, I used an extra set of contacts on the generator delay timer. When the timer expires, operating voltage to the shore contactor is interrupted, and operating voltage to the generator contactor is supplied.

-Sean
http://ourodyssey.blogspot.com

bobofthenorth · June 04, 2009, 03:15:46 PM

Quote from: Sean on June 03, 2009, 02:14:07 PM
Hey, look what I found. Once you posted the part number for the relay, I found the manual for your transfer switch:
www.escousa.net/Merchant2/graphics/00000001/LPT30TrblShootRepair020206.pdf
Looks to be an ESCO model LPT30, which is a 30-amp, 120-volt (only) RV transfer switch. So in addition to poor wiring practices, looks like they also forced a 120-volt ATS into a 120/240-volt application (which is why you now have the neutral problem), and too small to boot.

I agree that schematic looks remarkable similar to what I have but my relay has 120/240 stamped on the side of it right next to the UL/CSA stamp so its definitely a 240 volt relay.

Today I found a Parallax 5070 ATS at one of the RV dealers in Saskatoon. It was pricey but it would have been pricey to import one too - probably not much difference by the time it got here. The one I have switches all three poles, has a microswitch on the neutral contactor and has a built in delay which I think I can defeat in order to take control of how long the genset runs before I put a load on it. I'll need to get another spool of red wire in order to complete the install.

This unit also has a set of auxiliary contacts - one NO and one NC - but I think I'd need an engineering degree to figure out what to do with them.

Thank you guys for all your help - maybe I'll get around to posting some pix of the completed install - but maybe I won't if I find that spool of red wire.

We ended up tearing the ATS apart on the parts counter because I actually found a service manager who was more interested in learning than pretending he had all the answers. The documentation with the switch is pretty sketchy and we couldn't tell whether it switched the neutral so we tore it apart to see. I kept apologizing for being a PITA and he kept saying "no - we need to know this too." I like that attitude.

Sean · June 04, 2009, 04:25:19 PM

Quote from: bobofthenorth on June 04, 2009, 03:15:46 PM
I agree that schematic looks remarkable similar to what I have but my relay has 120/240 stamped on the side of it right next to the UL/CSA stamp so its definitely a 240 volt relay.

Bob, that's just the rating of the individual relay itself -- almost all such relays are rated for both 120 and 240. It does not reflect the rating of the transfer switch assembly as a whole.

Since Esco has always made quality stuff that properly switches the neutral, I conclude that what you have is, indeed, the LPT30 (which, as I already mentioned, is a 120-volt assembly but contains exactly the 120/240 relay you have), and it has been subsequently mis-wired to switch two hots instead of one hot and one neutral. That accounts for your neutral problem, as well as the mismatched screws on the terminal strip.

FWIW.

-Sean
http://ourodyssey.blogspot.com

bobofthenorth · June 04, 2009, 05:54:08 PM

OK - I didn't understand what you were saying but that makes sense. I think we gotta blame that one on Bruce BTW and now I'm not sure who to blame for the shore cord that we used to have. Up until we let some smoke out last spring we had this great big professional looking SS Marineco 50 amp connector and a shore cord the size of an adult python. The Marineco had leads running into a junction box and then from there the hard line ran to the panel. Last spring a screw must have loosened up in the junction box and eventually the smoke got out. When I started digging into matters to figure out where the smoke was missing I eventually discovered that my shore cord (remember - its the size of a python and it has 50 amp connectors on both ends of it) was only a 3 conductor cord. No problem there, is there?

There were a variety of locations where the two hots were tied together including the aforementioned junction box, the panel that I have already posted a picture of and the main panel. Up until now I had blamed all that on doofus and I'm still not sure who was responsible for that but this x-fer switch I think falls on Bruce. We're not big power users obviously because I had never figured out that we only had one leg. I think we had only ever been on 50 amp service maybe two times so we hadn't really ever tested it I guess.

Len Silva · June 05, 2009, 06:27:40 AM

Bob,

I'd like to return to the beginning of this conversation and question the need for warming up the generator for any length of time before loading it.

A little load management should take care of it.

I think 30 seconds is plenty of time for the transfer switch to operate as long as you are not slamming a 40-50 amp load on the genny. In addition, the air conditioners will have another 30 seconds or so before the compressor kicks in.

The big loads should always be turned off before connecting either to shore power or the genny and then turned on manually after connection.

A small (10-12 amp) load as soon as you have oil pressure and full speed will not hurt the engine.

If you are operating in sub-freezing temperatures, a moderate load will help it to warm up quicker.

Len

bobofthenorth · June 05, 2009, 06:48:07 AM

That is really good counsel Len and if it wasn't that my mechanic is the Super Uke I would thoroughly agree with you. There was some minute evidence of damage on my pistons when he tore the engine down. I don't suppose anybody else would have noticed or worried about whatever he found but after he got done yelling at me about how dirty the engine that I had just pressure washed was he started in on my bad operating procedures. This man has actually been thrown out of curling rinks for bad behaviour (apparently you can't throw your broom at a team mate who misses his shot - who'd a thunk?) but he is an exceptional mechanic. He'll probably never know what I do but on the off chance that he may find out I want to do it "right".

paul102a3 · June 05, 2009, 07:09:17 AM

Someone please educate me on the need to let the genset warm up before applying a load.

Again, I come from the boating world and it is normal practice to start the genset and hit it with everthing at once.

I understand that in a perfect world, warming the genset will increase the life span of the diesel but in the real world, does it really change much?

On the other end of the scale, allowing the genset to cool for a few minutes once the loads are transferred makes a significant difference in the longevity of the genset.

I am just trying to understand why this is so different than what I am used to.