Need help on AC convert to DC Power Supply

[vacek]

Our acreage gets a temprary high water table duriing the irrigation season.  As such we have French drains to our basement with a sump hole.  Currently about 30-35 gallons per minute is coming into the sump.  As a backup system I have a very nice DC powered sump pump rated at 5000 gallons per hour that is hooked up to a deep cell 12Volt battery.  The battery is connected to a power supply that is to  (1) kepp the battery charged and (2) power the system indefinitely  when if the primary pump were to go down but we still had AC Power.  At this point I am not sure the power supply is working.  Normally a green light indicates it is in mode.  However, the green light is out.  The dial is still accurately reading the battery so that part is working.

I need to test the system.  Here is my idea.  Let me know if I am on track or not.  I set my volt meter to the batter and while the power supply is plugged in I turn off the primary pump so the DC pump will activate.  At that point during the pump cycle I note the voltage.  Now I let the DC pump run with the power supply not plugged into the AC and note the battery voltage.  A lowering of voltage would indicate that the system is indeed working.

Is this correct thinking??

[WD45]

If you turn off the charging system and put a meter on the batt then you should see a voltage drop as the pump runs. The way I see it if you turn off the main pump so the DC pump kicks on the charging system should keep the batt from dropping below 12 volts as long as it still has AC power and if you put a meter on it you would probably see around 13 volts and more than likley around 14V. It takes more than 12 volts to charge a 12 volt battery.
This is kind of it in the proverbial nutshell.. Hope this helps

[efremtags]

You need to verify several things:

1) with AC power on, you should read 13.5V or greater on the battery. This means the charger has voltage output as a battery will never be that high of voltage in its natural state.
2) With the pump on (already started) power the pump directly from the power supply by lifting one of the DC power leads off the battery. This will be proof positive the power supply is working. Make sure the pump is stared from the battery, becsue the power supply will not likely be able to support the turn on surge.

The tests you mentioned will only test the battery, not the power supply. If you suspect an issue with the battery, it is  still a good way to verify the battery voltage does not collapse under load, which wold indicate a bad or near bad battery

[vacek]

Thanks for the information.

With the battery/power supply plugged in without the DC pump running I got a 13.57.  With the pump running and battery/power supply still plugged in I got a 13.63.  It increased.  With the pump running and the battery /power supply not plugged in the voltage went droped to 12.9 then stabilized at 13.1.

I will try the other test tomorrow.

[WD45]

As stated in the post above do not be suprised if the power supply will not run the pump or will only run after its already started. Most of those power supplies are only meant to charge and maintain the battery and run nothing independently from the battery. They do not have very high power ratings. I find most people do not understand power ratings.

[efremtags]

If it is a DC system, the charger has to have enough power to both charge the battery and run the load. If the pump can work with power on, and AC is on, and the battery voltage is rising, you have a well working system, and I would not bother testing any further.

For reference, the voltage rose becase you probably have a 3 stage charger, which means it will float @ 13.5, but will run an overcharge stage to 14.4 or there abouts. When the pump is on, the charger may have triggered to leave float and go into overcharge. If the battery is healthy, it will not be in overcharge for more than an 1hr. If you have a 2 stage charger (no overcharge), then you are just seeing some additional voltage drop becasue of the heavy current draw on the load. 

For reference I design battery chargers for a living.

[vacek]

Fantastic information guys.  EF....Thank you very much.  You have made my day and saved me $581 + shipping and handling.  That is what this little laptop cost.

[WD45]

From his initial post I assumed the DC pump was only there in case he lost AC power and the batt would run the pump until AC power was restored and was a very simple system. But there I go thinking again   Good info

[vacek]

WD45... Power failure was the primary reason.  In 1996 we had a transformer go out and our basement got 6" of water before we got a generator.   Since then of course I have a generator plus the DC Backup pump with the charger.  The secondary reason is if the primary pump fails then the DC will continue running indefinitely if "and that was the big IF" the charger is still working.  Right now I have about 35 gallons per minute coming in the french drains.  Not fun.  A lady up the road doesn't know how to irrigate and so se has flooder her field which the head of water percolates her already flooded field and here comes the water.   Also the Poudre river is much higher than normal this year and has remained high for well over a month over the norm.  My wife is really getting the tress watered with all that extra Aqua.