Bridging a 50ms tranfer switch gap. AC capacitor

basrijn · December 2013

Hi,

Was pointed to this forum by the friendly people at the Small Cabin forum. Recently finished the installation of my cabin power system. It consists off:
- Honda EU 2000 generator with extended run time setup (works awesome!)
- Cotek CX1225 battery charger
- Cotek ST1000 inverter
- Cotek CR6 remote
- A temporary 100AH battery (soon to be replaced with 2x Trojan 6V)

The Cotek inverter was chosen because of it's built-in 30A tranfer switch and low RF noise signature (I'm a HAM radio operator, the ARRL reviewed this inverter and it scored well).

The transfer switch needs 6-10ms going from battery to generator (and that isn't noticeable) but the switch from generator to battery can take up to 50ms. That causes the lights to go off-on and satellite model / wifi / pc to restart. I don't have a scope to check if the Cotek is indeed operating within spec and switching in 50ms. I'm assuming what I see is indeed 50ms

I'm looking for a way to bridge the 50ms gap. I understand the concept of a capacitor in DC, and was looking for something similar in AC. Lot's of hits for Airco start capcitors. If I understand their function correctly, they provide the extra kick the motor needs to start with needed a larger circuit. Also found references to a power factor correction capacitor. What I can't find is if this would help me solve my problem, and example circuit schematics.

Any hints on whether there is reasonable solutions to my problem would be most welcome!

Bas

mike95490 · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

You may have to put the sensitive components on a UPS to ride through the switching. Since it's AC, a capacitor won't help, it only stores DC and can't invent cycles for you.
For starting motors, Caps provide a phase shift between I & E and helps spin the motor up. You are a ham, this shouldn't be anything new to you.

BB. · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

If this is a pure off grid system--Just leave the inverter running 100% of the time and use the genset to recharge the battery via an AC battery charger when needed (continuous AC conversion is a very common method to provide clean power in a dirty power environment).

You will have some inefficiencies. Converting from AC to DC and back to AC:

0.80 typical battery charger eff * 0.85 typical inverter eff = 0.68 overall efficiency (typical worst case)

So, part of this depends on how much AC power you are using and how much you will be running the genset as to whether or not the double conversion losses are "too high" for your application.

-Bill

halfcrazy · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

Is the transfer time adjustable? A lot of chargers have here low voltage disconnect on the AC set to something really low like 70 volts or so. Try this with the generator running throw the generator disconnect and see if it has the same slow transfer. If yes then there may also be another adjustment. There may be one that allows you to pick how many cycles before it transfers. I am not familiar with the programming but I have run into this on Outback and Xantrex inverters and could usually tweak settings to make it work just fine

Blackcherry04 · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

As halfcrazy was alluding to. I don't know how you are breaking the input from the generator. It should be with a disconnect, if your just switching the generator off with it's cut off and letting it wind down till the power drops and then disconnects, it can be a problem. You want a clean disconnect. Some Inverters just have a issues with transfers, I'v changed all the boards and they still do it.

waynefromnscanada · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

Blackcherry04 wrote: »

Some Inverters just have issues with transfers, I've changed all the boards and they still do it.

Which brings us back to a UPS, probably the simplest, easiest cure, unless one is really familiar with electronics and likes trying possible tweeks.

techntrek · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

Yup, just stick your DVR, etc on a cheap UPS to ride out the transfer. Or go with the always-on inverter. I do both - small UPSs on the important stuff and a large UPS in the garage that runs everything 24/7.

basrijn · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

All,

Tx for all the replies.. One of the reasons I liked this inverter is that it has a build in (30A) transfer switch. This allows for larger loads to be run when the generator is going without having to deal with special sockets etc. It also means that I can stick to a smallish inverter instead of going bigger and always run everything thru the inverter. Wanted to keep it as easy as possible for guests. And it works brilliantly, nothing ever needs to be manually changed. You start the generator, the charger that is connected to a generator outlet starts charging the battery. The inverter switch the full power of the EU2000 if we need it.

I will contact Cotek to see if the cut-out voltage is adjustable. Nothing in the manual, and it;s a relatively cheap setup so that option might not be there. I'll probably add a DC capacitor om the one or two pieces of equipment (computer stuff) that I rather not have reboot. Lights etc I don't care.

I guess that a AC run capacitor is not something that applies in this setup.

TX all!

BB. · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

Nope, only thing a capacitor will do is create more problems (if it does anything).

Only other thing to do is wire up some "generator only" AC sockets and/or try another manual transfer switch such as a DPDT relay (or this $60 automatic switch) and see if it helps (don't use the AC inverter transfer switch).

-Bill

waynefromnscanada · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

basrijn wrote: »

I guess that a AC run capacitor is not something that applies in this setup.

Definitely not. Don't go there. An AC capacitor as mentioned earlier, cannot supply missing AC. When used with an electric motor, it shifts the angle between voltage and current only. Nothing else. It does not, and cannot supply missing AC power.
And as BB stated, installing one on an AC line in an attempt to supply missing AC will only cause more problems.

techntrek · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

A separate sub-panel just for the genset loads is a viable idea, too. Again, this is how my own setup works. A large genset feeds a sub-panel which only has larger loads on it, this sub-panel feeds the large UPS which then feeds another sub-panel with the more critical loads and lighting on it. Substitute "inverter" for "UPS" in that description and it would work for you, too.

bill von novak · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

basrijn wrote: »

I guess that a AC run capacitor is not something that applies in this setup.

TX all!

Nope. Outside of a resonant circuit that will "ring" at 60Hz for a few cycles there's not much you can do. (And a resonant circuit is a bear to drive; you even have to "sync" to it!)

waynefromnscanada · December 2013

Re: Bridging a 50ms tranfer switch gap. AC capacitor

bill von novak wrote: »

Nope. Outside of a resonant circuit that will "ring" at 60Hz for a few cycles there's not much you can do. (And a resonant circuit is a bear to drive; you even have to "sync" to it!)

And unfortunately, totally impractical for his needs.

inetdog · January 2014

Re: Bridging a 50ms tranfer switch gap. AC capacitor

waynefromnscanada wrote: »

And unfortunately, totally impractical for his needs.

More practical (and yet not practical at all) would be a motor generator with lots of flywheel inertia.
This sort of seamless (even at the subcycle level) transition is what an online UPS will handle. The load is always driven by the UPS inverter output and the AC input is just used to keep the inverter drain from drawing down the battery during normal use. And that suggestion has already been made....
If it only has to cover the transition from mains to generator the UPS would have to have a high output capacity but would not need particularly large batteries.

Bridging a 50ms tranfer switch gap. AC capacitor

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