Build a low cost semi-automatic generator transfer switch.

[Crossy]

Following on from my thread on the ultimate low-cost transfer switch we move on to something more advanced.

IMPORTANT (and common sense) Electricity can be lethal, the author / Thaivisa.com accept no responsibility for anything nasty that happens if you follow the posts below which are provided for educational purposes only.

Some basic electrical knowledge is assumed, please ensure you are competent to follow these instructions.

Many of us own low cost (cheap) emergency backup generators with simple (or no) transfer switches to switch from mains to genset power.

One of the most annoying (OK to me anyway) aspects of running a manual system is that you might miss the mains coming back on and continue using your genset (and your fuel) when everyone else is enjoying real power.

This simple and low-cost system will switch back to mains and stop the generator when power returns (handy eh?).

More follows:

[Crossy]

It is vitally important that your generator and the mains are never connected together, we don't want to be feeding power back in to the grid when the PEA techs are trying to get your power back.

Commercial Automatic Transfer Switches (ATS) use mechanically and electrically interlocked (read 'expensive') contactors. Recently some of the Chinese manufacturers have started supplying high power relays which are nearly as safe and equally robust, but at much lower cost.

We will use one of these relays to transfer the load between the mains and our genset.

Note I've been using this transfer system for some months now, no issues with anything getting hot or contacts welding.

You will need:-

• An 80 or 120A 2-pole change-over relay with a 220V coil http://www.ebay.co.uk/itm/350684868742?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 (NOTE the photo shows the 12V coil version, this item has the 220V AC coil required)
• A 0-3 minute 220V timer relay http://www.ebay.co.uk/itm/400498674114?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
• A box to put them in (our consumer unit has a DIN rail mounting so I installed the bits in there)
• 10mm² cable and crimps and the tool to apply (talk to your local sparky)

The timer relay is there to ensure that we don't stop the genset too soon if the power comes back for a short time.

Links are to sellers that I've used and who will ship to Thailand, find alternate sources (there are many) if you wish.

[Crossy]

The simple circuit:-

 

 

Important The pin numbers on the diagram do NOT correspond to the devices linked to above, I'm sure you can work out where to connect each wire (if you can't you really shouldn't be doing this).

 

Use 10mm² wire and crimp or solder ring terminals to connect the high current wires to the 80A relay, you won't be able to wrap the wire round the connection screws. You can use 2.5mm² wire to connect to the generator (up to 4.5kVA) or 4mm² for up to 6.6kVA. The other relay connections are all low current but do ensure the wire you use is rated for mains use.

 

How it works:

1. With mains power on and the generator stopped, the timer relay is energised and transfer relay K3 is de-energised and is feeding mains to the output, this is the normal operating condition.
2. When the mains fails the timer is de-energised and connects the transfer relay coil to the generator output (genset is not running yet)
3. When the genset is started the transfer relay coil is energised and it then connects the genset to the load.
4. Once the mains returns the timer relay starts and when it times out it disconnects the genset from K3 coil, releasing it and connecting the load to the mains.

We can now stop the genset. How to do that automagically is in the next post

 

I'll post some photos later

 

 

 

[Crossy]

99% of small genset engines use an electronic magneto ignition system, these require no battery to work simplifying life for everyone.

 

You genset's engine wiring diagram will look something like this:

 

 

In the 'run' position the ignition switch actually does not connect anything, when moved to 'stop' it grounds the magneto circuit (Bl wire) and stops the engine.

 

We can use this handy facility to automatically stop the engine when power returns.

 

All we have to do is connect pins 5 and 4 (normally-open contacts) of the timer relay between the Bl wire and ground, when the timer clicks in (power is restored) we short Bl to ground and stop the engine

 

 

Automatic start is rather more complex, once I have it working I'll continue

[bankruatsteve]

Looks great Crossy.

So, would J? be used to energize an ejector in my step son's bed? Well, that would only work 90% of the time.

[Crossy]

So, would J? be used to energize an ejector in my step son's bed? Well, that would only work 90% of the time.

I would connect him to the spark-plug output of the magneto, guaranteed to at least make him move slightly

[bankruatsteve]

At first, I ASSUMED that the diagram you posted was in "normal" position. But, after looking again, it seems like the timer has been de-energized (mains dead) and waiting for the genset. Or, have I killed too many brain cells?

In any case, I'm impressed. How do you find this stuff? Are the units from ebay the same ones you have? There's not much technical provided. (?)

[Crossy]

All my own work Mate (actually if you find a B&D Workmate I'm still looking).

The diagrams are actually shown with everything dead (as is convention) so in this case "mains off, waiting for genset", is accurate.

The units off Ebay are exactly what I'm using (I bought those), I want to ensure anybody who gets the urge to build one can get all the parts

Google will help you find technical info on the relays and timer.

I'm currently testing what has to be the cheapest / simplest automatic genset starter ever. Once I have it working t'will be published here for any and all cheapskates to use

OK, it's from an era before micro-controllers and the really clever stuff, I'm a great advocate of KiSS [Keep it Simple, Stupid]. My day job involves hi-tech stuff, computers, RFID, PLCs etc. etc. it's nice to design circuits that would have been cutting-edge (or at least clever) when I was an apprentice, just be thankful there are no valves / vacuum-tubes.

The kids today just look at a circuit consisting of a couple of dozen components (none of which has more then 16 legs) on a bit of Veroboard and wonder how it works without a computer

Off topic, but interesting (ish).

The really scary thing is that my son Andy who's in the RN (helicopter [sorry, "rotary-wing"] tech. for the Royal Marines, just done his bit in Afghanistan) has seen all the kit I worked on when I was in the mob, in the H.M.S. Collingwood museum http://www.rnmuseumradarandcommunications2006.org.uk/HOME_PAGE.html

When Andy was collecting his kit for deployment to Afghanistan, he says it was just like the old movies (I see nothing has changed in 35 years). Move down a counter collecting kit, boots, helmet, camo gear, Hi-Viz jacket....... hang on a sec, Hi-Viz?? Apparently, military thinking is that the camo gear is so the Taliban can't see you, the Hi-Viz is so the helicopter pilots can, obvious eh?

For some unknown reason the chaps were not happy being out in the open on a combat zone airfield with a big green X front and back, can't imagine why Revised kit apparently has the X only on the front.

[bankruatsteve]

Not trying to mess with KISS, but seems like it would be easy to add a "Voltage Band Relay" in front of the timer relay?

[Crossy]

Not trying to mess with KISS, but seems like it would be easy to add a "Voltage Band Relay" in front of the timer relay?

Indeed, a unit like this http://www.ebay.co.uk/itm/321111249358?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 would do the job nicely, apart from the cost

Let's keep this on the list of 'future enhancements'

[bankruatsteve]

So, if you want to cut power from the mains for some reason, would you open the 6a MCB? Does the xfer relay have any type of manual override to an off position?

[Crossy]

So, if you want to cut power from the mains for some reason, would you open the 6a MCB? Does the xfer relay have any type of manual override to an off position?

To cut mains power open the main incoming breaker The 80A relay does not have an 'off' position, it's either 'mains' or 'genset'.

Opening the 6A breaker will simulate a power failure, that will allow the genset to be started and once running the big relay will close and connect the genset to the building

[bankruatsteve]

Ah yes the mains breaker. And, that would not simulate a power failure? Just trying to think this out.

[Crossy]

I've been experimenting with this simple automatic start system. Obviously it needs a key-start generator, I'll detail the modifications you need to do to the genset in a later post.

It does work but there are pros and cons to such a simple arrangement.

First the circuit (pin-numbers are correct for the referenced devices), no prizes other than pride for the first to spot the 'deliberate' error:

Pros

1. It's pretty simple
2. It can be built very cheaply, many hobbyists will have the relays and switches 'in-stock', the only bits that are likely to cost are the Omron timer and the 220V coil relay (Ebay is your friend)
3. It draws zero power from the battery when the genset is stopped, so you don't need a mains charger

Cons

1. It has very little interlock protection for the engine. If the generator output fails (like you over-current it and the breaker opens) the circuit will try to re-start the engine with the predictable effect on the starter Bendix. Commercial units use the oil-pressure switch to monitor if the engine is running, my little genset does not have a pressurised oil system so I can't use that. I've mitigated the problem somewhat with the 'Starter inhibit' relay powered by the 12V output from the alternator, but it's not perfect, more thought required.
2. It only makes a single attempt to start the engine, if it doesn't fire first time, tough.
3. There is no over or under speed protection, or any other protection for that matter.

Help yourself if you want to try it, or use it as the basis of your own design, but do watch this space for a better (albeit more expensive) solution

Meanwhile my 2kVA inverter fried itself at the weekend, shopping required

[Crossy]

Ah yes the mains breaker. And, that would not simulate a power failure? Just trying to think this out.

Yes it would, but that would be a 'real' power failure and would stop Wifey's TV until the genset was started

Using the 6A breaker (which is needed anyway) means that you never actually need to kill house power whilst playing testing.

[bankruatsteve]

Crossy - you da man. Is that your Kwai Thong genset that you modified for LPG? Mine will absolutely not start unless I choke it. Then, it always starts the first time - of course then I have to restore the choke. That being the case, I think I will leave out auto-start - but may take on the rest of it.

Cheers!

[Crossy]

Crossy - you da man. Is that your Kwai Thong genset that you modified for LPG? Mine will absolutely not start unless I choke it. Then, it always starts the first time - of course then I have to restore the choke. That being the case, I think I will leave out auto-start - but may take on the rest of it.

It is indeed the same unit, mine wouldn't start on petrol without choking until I started looking at automating the choke. A small modification involving the angle grinder (!) and now it starts without manual choking (accidental result).

Our EP6500 genset http://www.kwaithong.com/product_detail.php?ref=do:read/id:2 is powered by a Chinese clone of the Honda GX390 13HP petrol engine, these engines are so close to the Honda units that you can use the Honda manuals to service and repair same (OK they're identical, even Honda parts fit)

Comparing the Kwai Thong choke arrangement with the Honda service manual shows a difference in the choke actuator rod, part 28 below :

The Kwai Thong part has an extra cross piece which pushes the choke back to the open (off) position, this is not needed as the vacuum actuator (part 27) does the opening and therefore the 'extra' bit can be safely removed to make the rod look like the Honda one (part 28). You can get the actuator rod out without removing the carb (it's a bit of a wrestle), modify it, then put it back (thus retaining the ability to manually choke if it's necessary to use the recoil starter).

Because the choke is no longer pushed open by the actuator rod the vacuum unit settles with the choke about 1/2 on when the engine is stopped, my genset will start from this partially choked position.

I do intend automating the choke properly (enter the 12V solenoid) mind as it does start quicker on full choke. A light spring to pull the choke fully closed (choked) would probably give enough extra choke to make starting easier, I need a fully automatic choke because of the LPG conversion (must not choke to start).

A job for the weekend when SWiMBO is at the Wat

Watch this space

[Crossy]

UPDATE

An experimental 'light spring' (OK, it's a rubber band) demonstrated that the idea works perfectly, with the engine stopped the choke goes fully choked, once the engine starts the vacuum servo pulls the choke rapidly to the fully open position.

Result!!

[Bcgardener]

What about brown outs or high voltages? These are the most common type of power disruption in Thailand and cause the most damage to equipment. Your system would not be able to deal with these? I manufacture power generation equipment and associated switchboards here in Thailand for a living. I can tell you that we have tried many sample Chinese contactors or power relays and would not want them in my house. Don't get me wrong some good electrical equipment does come out of China and we also use it but the relays you are suggesting do not fall into that category and why bother when you can buy a set of 25 amp ABB changeover contactors with mechanical and electrical interlocks for less than 1500 Baht.

Just my thoughts on the matter.

[Crossy]

Brown outs / over voltage are handled by our UPS and AVR, the ATS and genset was never intended to handle such.

Emphasis here is on low cost and minimal functionality, and you are right, there is no way I'd trust that '80A' relay with 80A continuous, at 30A it doesn't get warm so I'll happily let it live in my CU. Many of us cant run to USD 350+ for an ATS.

http://www.ebay.co.uk/itm/ATS-Automatic-Transfer-Switch-63amp-to-start-generator-in-case-of-mains-failure-/251343004687?pt=UK_BOI_Industrial_Tools_Generators_ET&hash=item3a8535e40f

The same relays are used in a number of commercial load-shedding units (no, not ATS) available on the net.

However, if you can point us at a RETAIL outlet (so I can buy one set) with 2-pole ABB changeover contactors (50A preferably, but 25A will do as I'm not expecting them to switch at full load) at 1500 Baht a set, I'll happily use them and recommend same to everyone. Control gear will obviously be potentially rather more complex than a simple relay.

Do you believe there is an actual hazard associated with these arrangements? If so please let the board-members know (here, not by PM) what it is so I can mitigate same, there is no way I would want to be associated with something that could endanger life.

If you want scary, have a look at what some people are suggesting doing on YouTube

[Bcgardener]

Brown outs / over voltage are handled by our UPS and AVR, the ATS and genset was never intended to handle such.

Emphasis here is on low cost and minimal functionality, and you are right, there is no way I'd trust that '80A' relay with 80A continuous, at 30A it doesn't get warm so I'll happily let it live in my CU. Many of us cant run to USD 350+ for an ATS.

http://www.ebay.co.uk/itm/ATS-Automatic-Transfer-Switch-63amp-to-start-generator-in-case-of-mains-failure-/251343004687?pt=UK_BOI_Industrial_Tools_Generators_ET&hash=item3a8535e40f

The same relays are used in a number of commercial load-shedding units (no, not ATS) available on the net.

However, if you can point us at a RETAIL outlet (so I can buy one set) with 2-pole ABB changeover contactors (50A preferably, but 25A will do as I'm not expecting them to switch at full load) at 1500 Baht a set, I'll happily use them and recommend same to everyone. Control gear will obviously be potentially rather more complex than a simple relay.

Do you believe there is an actual hazard associated with these arrangements? If so please let the board-members know (here, not by PM) what it is so I can mitigate same, there is no way I would want to be associated with something that could endanger life.

If you want scary, have a look at what some people are suggesting doing on YouTube

Crossy, I've got an ABB quote right in front of me A9-30-10 three pole contactors with auxiliary N/O contact (25A , AC-1) are 324 Baht each + vat. The 32A are 564 Baht each. Extra N/C contact for the interlock 80 Baht each. Not too sure on the mechanical interlock but I think it is only around 100 - 200 Baht. All of that is from our ABB supplier in Bangkok.

With the Chinese relays, who knows , there are so many companies there making this stuff. Whenever I get quotes from China the prices can vary from 100 baht to a 1000 baht for the same "item" but obviously quality varies as well. As you say, if you buy an 80 amp relay but only put 30 amps through it your safety margin is pretty good even if the quality of the relay is poor. We got some samples of Chinese copies of Schneider and ABB contactors with a significant cost difference (ABB 60 amp contactor: 1,420 Baht, Chinese copy; 400 baht). We loaded up the Chinese copy to 60 amps too see what would happen. the smell coming out of it was amazing, and probably toxic! We shut it down when the surface temperature of the plastic body went above 120 degrees 'C'.

You can buy an all singing all dancing PLC mains failure controller that will start/ stop and monitor the engine functions as well as a lot of other things to do with the power supply for around 15,000 Baht. I know this is too much for the average persons home but it is still a bargain. have a look at www.comap.cz .

[Crossy]

Does your ABB chap deal with the general public? That's better than 30% of my local 'pro' electrical retailer. Any chance of a name?

Remember, this is the DIY forum, where enthusiastic persons discuss Doing it Oneself (usually at the expense of commercial suppliers), but in reality, so few actually do Do it Themselves that the overall effect on profitability is truly negligible.

As noted earlier, do you see an actual hazard resulting from the use of a change-over relay rather than a pair of interlocked contactors, at the power levels we are envisaging?

[Bcgardener]

We buy large quantities (our order this week was 150k baht) but I think they would supply to you. You can only ask!
The company is Worldwide Procurement Technology Co., Ltd, contact K. Waraporn waraporn [at] wpt.co.th (from memory as not at work now)
I always like to have a mechanical interlock on c/o contactors in case something goes wrong although in 30 years of working with this stuff it has never really been required. It was just the way I was taught to do it so I suppose for a home set up you would be okay. You could always use two electrical contacts in series in case one fails. The worst case would be a mains feedback to the small generator. If it was running it would be more than likely out of synch so a large bang or shudder and probably terminal damage to the alternator. These small sets normally have capacitor regulation but I have noticed that even the Chinese ones over about 5.5kva have AVR's so that would definitely get fried. Apart from that I think things would be okay. If you would like any more detailed advice feel free to PM me.

Sent from my GT-I9300 using Thaivisa Connect Thailand mobile app

[Crossy]

Thanks for that BC, I'll contact them

Using a single relay with change-over contacts does effectively provide mechanical interlocking as only one contact set can ever be closed at once. If a contact welds for any reason the coil is not sufficiently powerful to bend the armature and let the other contact actually make. Contact clearance is about 3mm.

Of course there are disadvantages, there is no 'off' position (both contacts open) and you cannot control the delay between one circuit opening and the other closing (but it's definitely Break-Before-Make).

If I was not confident of the basic safety of this arrangement I would not have it in my home

I doubt that the relay would perform as well as contactors would under fault conditions, a dead-short across L-N when on mains would almost certainly weld the contacts before the 40A breaker opened. PFC measured at the incomer is only 1500A on our 15/45 supply so it may survive. I'm not going to test mind.

[Crossy]

OK, we now have a simple transfer switch and an automatic stop on the genset. Time to advance a bit to make the beast auto-start.

Firstly you will need a genset with electric start

Secondly it needs to start easily on a turn of the key without manual intervention (operation of the choke), earlier posts detail how to modify the choke on a Kwai Thong EP6500 or any generator powered by a Honda Gx390 engine or one of the Chinese clones.

The Beast in question, the round object bottom left is the K&N Garetson regulator for the LPG conversion (should have got one with automatic priming), the grey 'speaker wire' is the temporary 'stop' link to the transfer switch:

Electrical mods to the generator are simple in the extreme.

This is the Honda wiring diagram, the Kwai Thong engine is very similar:

To modify for remote start do this:

Hopefully the Battery+ and Battery- connections are self explanatory.

The 'Starter' wire (green on the diagram) connects to the starter solenoid, on my engine it's a black/white wire. It goes to the small blade terminal on the starter assembly. You can poke the wire through the hole in the blade and push the connector back on to make the connection.

The relevant connector is the blade above and slightly right of the two big connections with rubber covers.

The 'Ignition (Stop)' wire (blue on the diagram) goes to the magneto, on my engine it's a black wire which connects to a yellow at a bullet connector. This wire is the only one that goes across the top of the engine towards the spark plug. If there is a bullet connector in this wire (mine has one as does the Honda) you can slip the wire unto the receptacle and re-fit the bullet.

Not the best image of the magneto connection heading off to the magneto, the bullet connector where I attached the ignition wire is in the foreground.

To Test

With the engine ignition switch in the 'Run' position.

Briefly link Battery+ to Starter, the starter should operate and the engine start.

Once it's running, link Ignition to Battery- and the engine should stop.

Get this far and we can move on

Coming next, the simple solution to making your genset start on mains fail.

[Crossy]

OK as promised, the ultimate tight-wad automatic start for your genset.

I have ordered a pukka genset controller from China but whilst waiting for it to arrive I applied my cheapskate brain on how to achieve a simple and reliable auto start. The design shown here has no bells and whistles, no clever interlocks and start retries, but it does work (has started a dozen or so times since it was built) and is CHEAP!

It is intended to work with the cheapskate transfer switch and generator modifications shown earlier in this thread, but it should (possibly with minor modifications) work with any automatic transfer switch and electric-start genset.

You will need to be reasonably adept with a soldering iron (know which end is hot) but it's not beyond anyone, truly.

The circuit:

Shopping list (you will need):

• 3 x car type 12V 5-pin relays. these should cost <70 Baht each, current rating is not important but get >10A.
• 1 x NPE-Pro'sKit PK-3016 kit http://www.mynpe.com/more.php?data=014398673016 get it from one of the branches of NPE or order on-line http://www.mynpe.com/ (get the 40 Baht kit not the ready built one as we are going to modify it)
• 1 x 47uF 25V capacitor
• 1 x 0.1uF ceramic capacitor
• 1 x 1N4148 diode
• 2 x 1N400x diodes (x being any number that's available)

• Assorted choc-blocs, wire, spade crimps (and tool), the sort of stuff any DIYer will have in his workshop.

Instructions:

Cut the track shown "X" below on the PCB, it's far easier to do this before you install any components.

Build the kit BUT:

• Do NOT install R1, R2, LED1, R4 or C1
• Fit a link instead of R4 (use a bit of cut off resistor leg)
• Fit a 47uF capacitor as C1
• Fit R1 with a 1N4148 diode in parallel, check the photos for correct orientation, both legs will fit (just) in the PCB holes.

Yes, I know the board in the picture has R2 installed, it was something else in a previous incarnation

To test, connect 12V to the power terminals (yes I know they are marked 9V, the 555 is happy up to about 18V). The LED should light for about 5 seconds then go out, if it doesn't check you've got everything the right way round.

More in the next post

[Crossy]

The rest of construction is just connecting the bits together, note the connection to the coil of K2 from the timer is the yellow wire in this photo:

You can poke the wire through the hole where LED1 isn't or use a bit of resistor leg like I have.

The Mk1 on test on the bench.

To test connect 12V power, nothing should happen, link the two 'ATS' wires, both relays should pull-in, K2 (start) should drop out after 5 seconds or so.

Put it in a box, the relays are secured with double-sided tape.

Note that there is now a switch, single-pole, double-throw, centre-off (happened to be 'in-stock') which provides 'Remote', 'Stop' and 'Local' positions so you can start or stop the genset easily.

Revised circuit

If your genset has a 12V output that is NOT connected to the battery, you can use it as a 'generator running' signal to operate a 'Starter Inhibit' relay to give protection to the starter bendix should the cicuit trigger the start relay for any reason.

It works so well I wonder why I ordered the pukka controller.

Oh well, when it arrives I'll post about getting it to work, I've got a couple of extras I want to add such as a time clock to stop the genset starting in the middle of the night.

[yankee99]

This is great stuff thanks!

[Crossy]

This is great stuff thanks!

At least someone is reading it

Pukka controller seems to have got stuck in the revised HK customs outgoing mail procedure.

[Artisi]

This is great stuff thanks!

At least someone is reading it

Pukka controller seems to have got stuck in the revised HK customs outgoing mail procedure.

Well at least 3 of us have now read it. For me I don't have any need but found it interesting - good clear and simple instructions just hope someone can put it to good use. Well done.