24VDC Power Supply w/ AC from Generator?

Hi All,

We have a customer that has a system with several 24V power supplies in it. This has always worked fine when powered from the grid.

They now have an installation that is fed from a generator. Each enclosure (6 in all) has a starter for a single phase 2 HP 240VAC motor as well as the 24V system.

When more than 3 of these 6 units are turned on, the 24V systems drop out and lose communication with the master controller. This only happens on generator power, not on grid power. Adjusting the generator voltage up a bit seems to
actually make it worse. To make matters worse, the motors are starting under load. They drive a very, very small hydraulic pump that has to come up to pressure before I can shift the valve and start the cylinders moving.

We tried to put a surge suppressor (not believing it would really work) in the system but to no avail. It did not seem to have any affect at all.

Does anyone have any experience or success in applying 24VDC power supplies in generator systems? The specific power supply we are using in this case is found here:
http://eshop.phoenixcontact.com/phoenix/treeViewClick.do?UID=2866611&parentUID=&reloadFrame=true

Note, the generator is at least twice as large as it needs to be for the motor loads.

Thanks

How many pumps are they turning on at a time?

How stable is the generator supply voltage when the pumps are started?

SafewayBread said:

How many pumps are they turning on at a time?

Click to expand...

6 Pumps

SafewayBread said:

How stable is the generator supply voltage when the pumps are started?

Click to expand...

Voltage doesn't drop below 200. Power supply data sheet says it should be good down to 90V.

Is it possible to start one pump at a time?

I'm thinking that it must be somthing to do with the starting current the pumps are drawing. Can you use a Scopemeter to double check the voltage drop?

I had a wierd problem like that not too long ago on a piece of equipment. Had a 600-460 transformer then a 460 to 120. Had a small 1/4hp motor on the 120 system. If the motor started when another motor on the 460 side was running, half of the DC controls would drop out. I measured the voltage drop with my trusty Greenlee Multimeter, and it would show a drop to about 105V, about 22-23 on the DC side. Tried replacing a big list of things before I decided to hook up my Scope, turns out it was actually dropping to about 45V for about half a second, and getting next to nothing out of the DC power supply in the mean time.

What is the frequency doing ?

that looks like some kind of ps/charger/ups..... do you have a DC battery system connected to it?for that type of application I would setup 1 main battery bank with a charger and then feed each panel 24 volts.

diat150 said:

that looks like some kind of ps/charger/ups..... do you have a DC battery system connected to it?for that type of application I would setup 1 main battery bank with a charger and then feed each panel 24 volts.

Click to expand...

Whoops, the link was bad. That is what we were thinking we might go to. What we have is a regular power supply:
http://eshop.phoenixcontact.com/phoenix/treeViewClick.do?UID=2866268&parentUID=&reloadFrame=true

SafewayBread said:

Is it possible to start one pump at a time?

Click to expand...

The program would have to be changed. I won't be able to do that for a little but but it definitely wouldn't hurt.

Mickey said:

What is the frequency doing ?

Click to expand...

Unfortunately, I wasn't the one there with the scope. I didn't even get a trace back.

I was hoping that someone has had a similar issue before and could recommend a fix.

Norm

I assume 120 VAC single phase to 24 VDC power supplies with either rectifier and or SCR. Do they have ripple caps?


What are alternator ratings?
Does alternator supply the normal bus or just an emergency bus?

What is time span between loss of normal power and alternator on line and loading?? Could it be that selective loading does not have 24 VDC power supply energized soon enough? IS the 24 V power supply energized if on emergency bus?

How soon after engine start are you starting the pumps?

Could power supply ripple caps still be charging up when you start pumps?
Since this is a UPS what condition are batteries in? After deenergize is it trying to charge batteries and supply load all at once and getting overloaded?
Think I would try turning off power wait five minutes and reenergize to see what it does - do this on NORMAL power.

What does frequency and voltage do when you start a pump? If a large load you should see any speed fluctuation on engine tach (if you have one) you may be able to hear engine slow for that split second.

What is percent load on alternator when all this happens? If 50% with nearly all loads energized I dont think you have a governor problem.

I also wonder about the master controller - maybe it is the problem and not 3 power supplies??

Dan Bentler

Looks like it is proably a switch mode. Phoenix is normally good stuff. Suggest the problem may be harmonics from the generatort. Worth a look.

diat150 said:

that looks like some kind of ps/charger/ups..... do you have a DC battery system connected to it?for that type of application I would setup 1 main battery bank with a charger and then feed each panel 24 volts.

Click to expand...

I would try this too. I would simply purchase a 24vdc UPS. They are getting pretty common and would be an easy thing to try.


http://www.phoenixcontact.com/signal-level-matching/31263.htm
http://www.trcelectronics.com/Meanwell/ups-module.shtml
http://www.solahd.com/products/ups/sdudcups.htm
http://www.automationdirect.com/adc...ules_(RHINO_PSM_-a-_PSP_Series)/PSM24-BFM600S

My appologies to all. My first link was wrong. All the power supplies are regular (non-ups) 24 volt switching power supplies.

They are not located near each other so running a common DC system is problematic. I have a 4 wire cable running to each power unit. 2 black wires are the 230 VAC. A white neutral wire between them (ie from either black to white I have 120 VAC) and a ground wire. Right now I'd love to be able to keep working with that.

The power supplies are all supplied by 230 VAC right now. I'm thinking to change that to 120 VAC to see if there is something going on because the ground wire on the power supplies is probably bonded to the neutral somewhere?

I have had exactly the same problem and it is down to the fact that not all 24V power supplies are equal. You may be able to fix it by only starting one motor at a time, otherwise you will have to spend some money,

Two differences:
Though the power supply is rated from 90-260Vish they can't cope with variations. If you start at a volatge then you have to stay with the +/-10% of that voltage (the data sheet will give the exact range).
Next issue is how the supply copes with loss of Mains, some switch the output off straight away but some have largish output capacitors and let the voltage droop. I can see the reason for cutting the output voltage when the supply starts to go, it protects the supplied devices from wrong voltages, but causes problems with brownouts.

I had used PULS power supplies instead of my normal Siemens units, went back to Siemens and the problems went away. It sounds obvious but the way to know what type of supply you have is to watch what happens when you cut the Mains power, does it switch off instantly or does the output LED stay on and then fade.

If you don't want to replace the power supplies then look at adding Buffer modules:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=7141274

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5055421
They are capacitor rather than UPS battery based.

regardless I would look into getting some type of battery power to filter out any issue when the generators swapover. somethign like your first link with a small battery would probably eliminate your issue.

You should check your generator sizing. When you kick on a pump the current inrush is often 5 or 6 times FLA. Generators must be sized to handle the kVA, not kW. Also, if your power supply or VFDs make a significant portion of total load the harmonics can compound the effect of current on the generator set.

Your suspicion of grounding is also well placed - poor grounding will compound the above.

What does the generator manufacturer say?