HELP!!! Transfer Pump Watering Garden

[Jonessmj]

I’m running into issues with a setup I’ve put together nd can’t figure out if I’ve sized things correctly or not.

My Setup:
1. Rain barrel connected to a 12V DC Transfer Pump https://www.harborfreight.com/12v-dc-transfer-pump-290-gph-63324.html

2. Transfer Pump running off 12V deep cycle 18ah battery. https://www.amazon.com/dp/B00K8E4WAW/ref=cm_sw_r_cp_awdb_t1_qFc0Eb725A644

3. Battery being charged by 20W solar Panel and charge controller https://www.amazon.com/dp/B0836CM9FJ/ref=cm_sw_r_cp_awdb_t1_ZDc0EbY3CZKE6

This is my first solar project and I’m not an electrician.

I tried hooking everything up to the charge controller but the pump would not run. So, I hooked the pump directly to the battery while leaving everything else hooked up to the charge controller. The pump worked, but for less than 10 mins at which point the battery couldn’t run it any longer. I’ve checked the battery voltage for the last 3 days and it’s gone from about 11.7V to 11.82V in 3 sunny days. I checked the voltage coming off the solar panel before it gets to the charge controller and it has been 20-21.xxV around 3pm est. I didn’t check the voltage from the charge controller to the battery, but can - what should I expect?
Given all of this info and the equipment I linked to, am I doing something wrong? I want to run the pump for 20-30 mins 3-4 times per week. Is that possible with this setup? If not, any suggestions? I’m at a loss at this point.

 

[gnubie]

It looks like your solar panel + charger simply are not up to the task. Your battery is constantly undercharged from the voltages you have posted.

First thing to do is work out just how much power that pump is using in the 20-30 minute run. The current draw will vary depending on the change in height of the water, so if you have a DC clamp meter or can borrow one that is probably the easiest way for you to check. Hook the pump up to a fully charged 12v battery or suitable 12v power suply, check the battery voltage as it will drop under load, and check the current at the same time. Once you have that you can work out how much power you need to get from your solar panel. If you don't have access to a meter does the pump have a current rating on it? That figure would let a worst case power use figure be calculated.

When you measured the panel voltage at ~20v at 3pm, was the panel connected to the charger controller, and the battery to the charge controller?

Suppose the battery voltage is measured at 12.8v and the motor current is 2 amps. That's 25.6 watts (volts x amps), giving approx 13 watt hours (25.6 watts for half an hour) of draw per day the pump is run. Your charge controller is a PWM style, at least from the pages I found with Google. There aren't any details about the panel on the Amazon page but with a PWM controller it is entirely possible you are throwing away 1/3 of the panel's power output so now the power out of the charger is more like 13 watts, peak so now you have to replace that 13 watt hours, and then some considering battery self discharge etc, with 13 watts of power, ie, at least 4 hours of good square on sun on that panel due to the difficult nature of lead acid charging. This is not necessarily your actual circumstances, but it should give you an idea of what is going on.

 

[Jonessmj]

Thanks for the reply. You are correct regarding the fact that the panel is connected to the charge controller and the battery is connected to it as well. I did measure the voltage coming out of the controller and to the battery during that same period at 3pm and I believe it was ~13V. So your example seems spot on.

What type of controller do you suggest to minimize the voltage loss from the panel to the battery?

I’ll report back the voltage under load and the current.

 

[gnubie]

If you can measure the current into the battery with the sun perpendicular to the panel (best sun exposure) and the voltage on the battery at the same time that will let us see what the actual charging power of your PWM controller + panel is.

A cheap MPPT controller might well do better, but the actual charging power from above will say if there is any point to getting a MPPT controller, it may just not make enough difference alone.

 

[Jonessmj]

Ok, I finally got around to taking the measurements

The voltage of the battery was 12.07V and the current from the controller to the battery was .025A. These readings are from the battery I plan on using.

I wanted to run the pump today so I used a fully charged battery from one of my kids ride-on toys. It’s an 8ah battery that was reading 12.82V before I ran the pump and read 12.53V after 10 min of run time.

I’m not an electrician so hopefully I got you what you were looking for.

Thanks!

 

[gnubie]

Is that .025A right? That's hopelessly low current under full sun conditions. With the PWM controller and panel in full sun I'd expect to see at least 0.5 amps. If that is all you are seeing into the battery something is wrong, unless you had the pump connected and on at the same time.

Maybe draw a rough circuit diagram and post some pictures of the wiring configuration you actually have and I can look at it from afar and spot a problem.

 

[Marty4321]

Did you ever resolve this? I am curious if you just ran the pump directly to the battery and let it run to see how long it lasts? The pump specifications show it operates at 50 watts at 12 volts DC. That is a little over 4 amps. The battery is 18 Amp-hours. The math says you should get a lot more run time. And like posted above, if you are working with this stuff it is best to get a meter that you can clamp around one of the wires to measure the DC current. https://www.amazon.com/UT210E-Handh...eywords=dc+clamp+meter&qid=1593301208&sr=8-20