1. Home
  2. Electronics Design
  3. AC Voltage Conditioner for Appliances on Generator Power?

AC Voltage Conditioner for Appliances on Generator Power?

Hello -

I have company that makes small, low flow, high-pressure pumping systems.

The systems consist of small digital controller (MSP430 based) with an LCD display. The pump motor plugs into the controller and power is supplied to the pump motor via a relay inside the controller, i.e. there is only one power cord for the unit. The units are designed for

120V 60 Hz power. When the pump motor is running, the steady-state current draw is 7A, when the motor is not running, the controller draws 300 mA.

Recently a number of our systems have been installed on small Caribbean islands that have powered supplied by diesel generators. We have had an issue with the controllers failing - either via the fuse blowing, or the micro getting fried. Since we have near perfect reliability with the systems on domestic utility power, my guess is that either power spikes or electrical noise from the generator power is causing the failures.

The purchaser of the systems in the Caribbean has told us "everything else here works fine so yours should too", while our contract electrical engineers are giving us the "we can't be responsible for anyting running on generator power". I haven't had much luck Googling around on the topic.

So, my question is: what options would I have as far as some sort of reliable voltage conditioning device that could strip out any electric noise and/or provide surge suppresion when the units are running on the generators? I need something that could be incorporated into the unit for < $75.

Thanks

Reply to
cwrm4
Loading thread data ...

You probably need a better voltage regulation circuit. Can you post your design?

Reply to
linnix

Try this....

formatting link

...I believe this schematic constitutes the voltage regulations/ transformer circuit (apologies but I'm a ME not a EE!). The rest of the board just contains some additional relays for other devices that the controller triggers. The LCD and micro are located on a separate boad that is piggy-backed onto the power board.

Reply to
cwrm4

It can't be driving the micro with 11.6V. What's between the 11.6V and micro?

Reply to
linnix

This:

formatting link

and here's where it ties to the micro:

formatting link

Reply to
cwrm4

I would double check on your LM317 design. It doesn't look right.

Reply to
linnix

The "we cannot be responsible etc" is _too_ true. The output of starting and stopping generator is a mess of voltages and frequencies till it stabilases. So any device connected during this time can fail. One of simplest things would be a time delayed relay on line, activated by line voltage and connecting the pumps and controllers after ~1 minute. When connected beware of stopping generators.

HTH

Stanislaw

Reply to
Stanislaw Flatto

That's very true. Nevertheless, a properly designed regulator circuit should be able to prevent damages. The OP's circuits are wrong and very inefficient. It doesn't make sense to have 12V transformer/ switcher output and wasting 75% of it in the linear regulator. 300mA for an LCD controller is ridiculous if not illegal. I am not sure if we are still on track to ban such linear regulator by law.

Reply to
linnix

You have big problems doing this cheaply because you tap off the internal line feed to drive the pump. Might as well figure 1KVA for whatever you do.

Reply to
Fred Bloggs

Very hard to say without seeing the whole unit. It is best to get a local consultant to take a look at how it is wired, where the cables are running and so on.

This will be more a shot in the dark but has helped a few times: Get a linear regulated power supply of a good brand, such as Condor. Proper amperage with lots of reserves, it can get hot in the Caribbean. Should be one that has a uA723 chip for regulation (most do). Adjust that down from 12V to 11.6V, place a good inline power filter up front. The Corcom brand is good. Fuse it all properly.

A Corcom filter alone right in front of T1 might also work. Use a good filter, not just a common mode choke. Right now it seems you have nothing like that in front of T1, that lone transzorb isn't going to cut it. The motor power should be tapped off before that filter.

Keep in mind that spikes can also come in via control lines into the controller board and then you'd really need a consultant that knows EMI stuff well.

With generators you need to be prepared for lots of brown-out conditions. Slow and sputtering starts, running out of diesel, big loads being switched where voltage and frequency can go all over the place etc.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Feed the input voltage to the MC34063A through a diode installed before the R8/C6/pin 6 junction, and add a 100 uf from that junction to ground. On the output side, change C15 to 270.

You can also add the optional output filter to the MC34063 - see the datasheet. What is the purpose of R1 and R6?

Ed

Reply to
ehsjr

Change the power supply to an offline SMPS, they do not care what frequencies they receive, and if done correctly can have a wide input voltage. Low cost off the shelf units can easily handle from 90V DC to over

250V AC with out a glitch. Sounds like your product is low volume, so I would not try to roll your own due to regulatory testing. The good news is some are available with several voltage outputs, so you may be able to eliminate your other power supplies entirely, potentially saving money! Efficiency would improve also.
Reply to
Jeff L

There are also huge "magnetic stabilizer transformers" that were popular in the former Eastern block countries because the power grid was often so lousy that TV sets would repeatedly use sync or something would fry in there. Those monsters must still be around somewhere.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Fried an oscilloscope once with one. The thing didn't get along with its load (a few old non-PFCed SMPSes, only 50% of rated stabilizer power). Stabilizer overheated, produced weird 100Hz (!) output harmonics, and fortunately it was the cheap TDS2xxx scope that went first (got it repaired on warranty).

I didn't really bother to investigate the cause of the weird behavior, I just chucked the whole damn stabilizer into the bottom of some cabine where I'm sure it still is today. It's a 1.5kVA unit made by Block. Maybe it has some future use as a gravity lens.

robert

Reply to
Robert Latest

Some scopes in the TDS series are truly deplorable IMHO. That's why I recently bought an Instek instead.

Watch out for that nasty conducted EMI at around 40/80kHz. It can really fool you when looking at analog signals. Probably leakage from the backlight inverter or maybe its switcher.

Well, you aren't supposed to connect switchers and PFC stuff to it. They weren't meant for that. In this thread it's a simple air conditioner where 99% of the load is motors.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

I didn't have time to dive into all this. Let me just say that if the generators are configured to provide backup power, (automatic transfer), then you'll sometimes see systems that do not bother to synchronize the Utility-provided AC waveform with that provided by the backup generator. They just throw the switch when normal utility returns.

So, when the automatic transfer switch goes back to Utility power, it's possible to switch the load from the max voltage of one souce, to the min voltage of the other. There are also usually slight frequency variations between the two sources, but this is likely unrelated to your experience.

If any of this is the case, your customers really need an in-phase monitor on their automatic transfer switches. (If manual, it probably takes too long to throw the switch?, and this problem would not occur.)

I agree with other posters here that a robust power supply on your end could be designed to handle utility transfer switches for generators if you feel there is a reasonable design justification for same. Good luck.

-mpm

Reply to
mpm

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.