One for the sparkies

mariusmeyer

mariusmeyer

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I need some input/explanation here please.

I finally connected my battery backup and tested it to see how long it will keep my return pump running.

This is what I have. 145W return pump, 102AH deep cycle battery with built in state of charge indicator Green for 70% and up, black when less than 70%, new and fully charged. Inverter is pure sine with an efficiency of 86%. 3 stage charger.

So according to my calculations the pump will draw 14.05A from the battery. (145W/0.86%)/12V

For a full discharge of the battery it would be 102AH/14.05A = 7.25 Hours or 7hours:15mins.

I monitored the battery voltage throughout the entire time (I know it is not an accurate estimate of state of charge) to see where it is. The battery started off at 12.4/12.5V. After 7 hours of running the pump the voltage was down to 11.9V and the state of charge indicator was still green! How can this be? I thought that the state of charge indicator is not working as it should. So I switched the pump back to mains and let the battery recharge. I expected it to recharge for around 16-24hours as it should have been close to dead according to my calculations. Yet after 6.5hours, the battery charger indicated that it was in float charging mode.

So was my calculation on running time incorrect? Is my pump drawing that much less power? Or do I have a super battery?
 
The current flowing thru the pump is the wattage divided by the rated voltage, thus :

I = 145 / 220 = 0.66 Amps
 
Last edited:
is the pump 12v or 220v?
 
i would prob do it the dangerous way, use the multimeter probes to connect the live pin to the live socket in series :)
 
Cool. I like your style. That is what I thought I had to do but was not sure if thats how it gets done. I will just find a break in the live wire and measure it before and after the switch.
 
good luck, but be careful. i did a similar thing the other day trying to see how much current an external lamp was drawing. done it a million times before, got complacent and careless. long story short, my hand clamped on the live and i was dancing around like a maniac with my father laughing his head off... :yeahdude:
 
danimal said:
good luck, but be careful. i did a similar thing the other day trying to see how much current an external lamp was drawing. done it a million times before, got complacent and careless. long story short, my hand clamped on the live and i was dancing around like a maniac with my father laughing his head off... :yeahdude:
Click to expand...

Nothing like parental love.
 
Put youre meter in current mode and mesure across the switch while it is off less chance of geting zaped with having loose wires floting around.
Got zaped myself the other day while working on the 3 phase supy to a pump station 200kw pumps 380v acros the forarms will shake you up a bit and leave some not so plesant burn marks supose that what hapens when you work 23 hours strait

marius your calcs seem 100% I wouldent trust the state of charge reading on the batery as it is only a gide to batery health realy. if you want your batery to last I wouldent go below 50% discharge too often on even on suposed deep cycle baterys.

on the charging issue youre batery will charge the first say 80 % quite quickly then the charger will switch to float mode witch takes a long time to get it 100% just the way the battery charges no falt of the charger just the way the charging curve goes on lead acid batterys.

btw this and much more knowlage was gaind from years working in marine electronics industry which is mainly 12v battry systems (on ocean going yachts)
 
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