How to know operating voltage for load?

[rubberlele]

Hi everyone!
I would like to ask, lets say if i have a simple circuit as shown, how can i know the operating voltage of pump? should i put voltmeter accross the load? Let say if i put an oscilloscope in the place of voltmeter, the voltage across the load will slowly decrease right? can i say that the decreasing voltage is the performance of the battery?

 

[akg]

Hi everyone!
I would like to ask, lets say if i have a simple circuit as shown, how can i know the operating voltage of pump? should i put voltmeter accross the load? Let say if i put an oscilloscope in the place of voltmeter, the voltage across the load will slowly decrease right? can i say that the decreasing voltage is the performance of the battery?

with the ckt given u cannot get the operating voltage of the pump. because a 12v rated motor will run if it is given 15v.

u donot need an oscilloscope, u need a voltmeter an ammeter and a clock to measure the performance of the battery(s)

 

[rubberlele]

so, akg, wat do you suggest, a true newbie here... :?

 

[Nigel Goodwin]

so, akg, wat do you suggest, a true newbie here... :?

For a start tell us EXACTLY what you are trying to do, and why?.

 

[rubberlele]

Yeah Nigel, wat im trying to do is, i wanna run a dc diaphragm pump, currently i connected the pump directly with 2 12V-7.2Ah batteries(connected in parallel). I found out that after i switched on the pump, the pump will run smoothly and after sometime, the pump will become slower and slower and then stop. So wat i wanna know is, wat test can be done here, i mean simple test, since im a newbie

 

[Nigel Goodwin]

Yeah Nigel, wat im trying to do is, i wanna run a dc diaphragm pump, currently i connected the pump directly with 2 12V-7.2Ah batteries(connected in parallel). I found out that after i switched on the pump, the pump will run smoothly and after sometime, the pump will become slower and slower and then stop. So wat i wanna know is, wat test can be done here, i mean simple test, since im a newbie

As it works fine initially, it's fairly obvious that it's just the batteries running down - monitoring the voltage will just prove it, but there's not really much need?.

How long does it actually last?, and running the batteries conpletely flat is most probably damaging them, substantially reducing their capacity.

Probably a more useful test would be to measure the current they take, in which case you put an ammeter in series with the motor - but you need to ensure you have a large enough range on your meter, it could be taking tens of amps? (depending on the size of the motor, and the load upon it).

 

[akg]

Yeah Nigel, wat im trying to do is, i wanna run a dc diaphragm pump, currently i connected the pump directly with 2 12V-7.2Ah batteries(connected in parallel). I found out that after i switched on the pump, the pump will run smoothly and after sometime, the pump will become slower and slower and then stop. So wat i wanna know is, wat test can be done here, i mean simple test, since im a newbie

one more thing to make sure that. is the o/p of the pump is smooth flow? ie is there any resistance buildup to the flow .

 

[rubberlele]

i think i will do the ammeter test, and akg, since its a dc pump, it has low flow rate, like 5l/min max..

 

[rubberlele]

I have another stupid question i think, hmmm i have 2 solar panels, Kyocera 120, each solar panel has max power 120W, what i did was the solar panel charge the battery by going through a charge controler, this works fine.
However, this morning, i did something(maybe stupid or not i dont know), i connected 1 solar panel directly to the pump. The pump operates slowly, its like when a battery nearly totally discharged. Not sattisfied with this, i connected both solar panels (in parallel) and connected them. The pump works fine. The pump's power should be 40W according to the manufacturer's manual. But i wonder, how could this be? Im thinking of doing a test by measuring the voltage of the pump when it operates, and then connect a resistor in series with the circuit, measure the voltage across it and then calculate current by using ohms law. Any opinion on this guys?

 

[Styx]

just because some solar cells say they output 120W MAX doesnt mean they were when you were testing.

That MAX was prolly in a lab with an Effing big lamp shining right at the cells

You dont state your location so acssuming you are in the UK we havn't had any direct sunlight for months.

no direct sunlight = no where near full power from teh cells

 

[Nigel Goodwin]

Yes, 120W is a theoretical maximum - think Sahara desert at midday!.

 

[rubberlele]

Im from Malaysia, we receive high solar radiance

 

[rubberlele]

Now i have another problem...in the picture, i have solar panel which can directly on the pump and two 12Volts battery which can on the pump. Im hoping that somebody can give me a circuit that can charge the battery when the battery's voltage drop below say 11V, and after finish charging, the pump continue to operate directly from solar panel. I've heard something about relay, and hopefully somebody can give advice on this. Thanks!

 

[Styx]

Im from Malaysia, we receive high solar radiance

What you say is high and what the solar panel needs to produce maximum power are going to be alot different

You could be right and you do have enough sunlight for the solar-panels to convert alot of power, then the only thing it can be is extra load on yr machine.

Load ~ current
speed ~ voltage

and power is torque x rad/s

 

[rubberlele]

mmm how can i know the extra load wont damage my machine?

 

[Styx]

mmm how can i know the extra load wont damage my machine?

you need to check the current rating of the motor

 

[rubberlele]

yeah max current for the motor is 7A, and when the pump runs, the current is 2.5Amaximum(directly from solar panel), i think it should be okay yeah?

 

[gerenis]

Hi Rubberlele,
I'm not much into batteries, possibly not all information below is 100%correct. It's worth considering though.
Any comment or correction from the more experienced is welcome.

I think it's risky to connect the solar cells directly to the battery. If you do so the charging is uncontrolled. When the load is on and the sunlight is weaker, there may be no problem. Then you forget about it or switch off the load and leave them connected for too long... The battery may be degraded or damaged if it's overcharged.

Damage done to the battery can be the reason for the batteries not being able to supply current for a longer time.

The solar cell charger circuit you posted on another topic earlier should be OK to provide a controlled charging. But it should be fused IMO (for fire risk), especially if a high capacity battery is used.

I think paralleling batteries can degrade or damage the batteries, if they are not of identical type. If the batteries are identical type, but one was more run down than the other (i.e. they were not on the same voltage) while connected the first time, it can also cause damage. The stronger battery discharges into the weaker one at high current. So once connected parallel, then they better be kept parallel ever after so to prevent different voltages developing across them.
All in all there may be safety issues and potential problems of connecting certain type of batteries parallel.
You can check out the "Parallel batteries" section on the following web page (though it deals with bigger batteries used an autos and boats):
**broken link removed**
Quote from that page: "from a safety perspective, if one battery develops a shorted cell then the other one will boil itself trying to bring the first one's voltage up". You can see there a blown up paralleled lead-acid battery...

 

[rubberlele]

Hi there gerenis! Thanks! Yeah i realize that too, i've discarded the battery from my PV system, now the solar panels power the pump directly, and for switching on and off, i've decided to use LDR which will trigger a relay. Just now, i found out that at 5.00 p.m and over, if its cloudy, my pump wont run. But other than that, it will run just fine. Thanks mate