Pump won't start on power from Inverter

Sitesure · December 2018

I have a small aquaponics setup and I'm trying to wire a battery backup system to kick in for a few hours when grid power is down. Everything is working except the pump won't run off the inverter (which, of course, is the main reason for the entire exercise lol).

Trupow Frequency Variation Pond Pump 1400 gph 20 watts
POTEK 750 watt Power Inverter (modified sine wave)

A small 2 watt air pump does run with no apparent problems off the inverter.

Is it the modified sine wave causing the issue? Is there a way to easily correct it.. or am I looking at needing a new inverter? Or is it something else entirely?

Thanks,
Bill

pdh · December 2018

What kind of battery are you using? Your problem could be lack of battery capacity, rather than trouble with the inverter.

Side note: I did a quick online search for that pump and the docs I found say that it draws 40 watts, not 20. Are you sure of the 20-watt rating?

mike95490 · December 2018

for pumps, you really need to use pure sine inverter

Sitesure · December 2018

Battery is a 12v 35AMP "Thunderbolt Magnum Solar" (admittedly a Harbor Freight special).

I was unable to track down the manual for the pump so quoted the stats from the Amazon listing -- you're probably right at 40w. But even at 40watts the draw should only be 1/3 of an amp, right?

Sitesure · December 2018

mike95490 said:

for pumps, you really need to use pure sine inverter

That's beginning to sound like the issue <sigh>.

pdh · December 2018

Sitesure said:

Battery is a 12v 35AMP "Thunderbolt Magnum Solar" (admittedly a Harbor Freight special).

I was unable to track down the manual for the pump so quoted the stats from the Amazon listing -- you're probably right at 40w. But even at 40watts the draw should only be 1/3 of an amp, right?

Power (watts) is voltage times current, so a 40-watt load would require about 3.3 amps from a 12-volt battery. Your battery (35 amp-hours, not 35 amps) should be able to deliver 3.3 amps if it's in good condition, but I wonder if the pump draws more than 40 watts at startup.

I thought that the main problem with modified square wave inverters and pumps was that the non-sinewave voltage can make the pump's motor run hotter than usual, thereby shortening its life. But I don't run a pump myself so I may be wrong about that.

Another question: what kind of cables are you using to connect the battery to the inverter? Poor cable connections, unreasonably thin cables, or very long cable runs can also cause problems. And: if you measure the battery voltage when it's trying to start the pump, what voltage do you see?

Estragon · December 2018

As noted above, MSW inverters often don't play nice with inductive loads like motors. Also, starting amps on motors can be several times running amps.

How is the inverter connected to the battery? Car DC plugs typically aren't good for much over 10adc or so. Clips can also be problematic. With a surging load, and possible flaky connection to a fairly small battery, voltage drops, so more current required to run the load, which is taking more anyway because of the square wave.

In this application, maybe a dc pump direct to battery might work better?

Sitesure · December 2018

Battery has a full 12 volts. Inverter is connected direct with 12 gauge solid-core wire, no clips, wrapped around post and tightly connected on both ends. Interestingly, I see no change in voltage, and the inverter shows now changes in input or output when attempting to run the pump... its like it isn't drawing anything at all.

The square wave didn't bother me, when planning the system, because I didn't plan to run the pump long on the backup system and it is water cooled. So most of the adverse affects should be fairly well mitigated.

I, obviously, didn't think the square wave would prevent the pump from even starting.

BB. · December 2018

It appears that your pump may have a VFD built in (Variable Frequency Drive). Many "simple" electronic power supplies with AC input use a pair of diodes and a high voltage capacitor to rectify AC to DC power... Then convert the DC back to (guessing) 3 phase variable frequency power for a permanent magnet motor. (I could not find much information about this pump).

These types of power supplies can be pretty hard on a MSW (modified square wave) AC inverter's output. Or it may work just fine...

If you have a 40 Watt (25-60 Watt) filament lamp you can put in parallel with the pump, see if the stable AC load will make everything work OK? Not a good chance of helping, but a common thing to try on inverter and generator outputs with "difficult" loads.

-Bill

Estragon · December 2018

As a matter of interest, have you confirmed pump works as intended using grid AC (to rule out a problem with the pump)?

Maybe a typo or me misunderstanding, but "battery has a full 12 volts" is a bit confusing. At 12.0v, the battery would be a little under 1/2 full.
https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html#Battery Voltages

Sitesure · December 2018

Estragon said:

At 12.0v, the battery would be a little under 1/2 full.
https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html#Battery Voltages

My ignorance is showing, thanks for the link. Continuing to charge it now.

The pump has been running on the grid with no problems.

I'll also try the parallel load idea too.

Thanks.

jonr · December 2018

I'd try it when connected to a known good/charged battery - like your car battery.

Sitesure · December 2018

Thanks to everyone for the assistance. Wanted to update everyone, looks like I had two issues.

First was having a modified sine wave inverter, switching to a pure sine wave one fixed the issue. In fact, power went out last night and it switched over and ran with no issues.

The second problem was the solar cell and charger controller weren't getting a full charge on the battery. It is possible the original inverter was drawing too much power. At any rate, I've set the solar system aside for now and am using an AC battery maintainer, since the purpose of my setup is to drive the pump during brief grid outages. Once I have a few spare moments I'll explore the solar charging again.

Thanks all!

BB. · December 2018

Check that your battery maintainer is not overcharging the battery... Your battery should be at float (once fully charged) around 13.4 to 13.6 volts or so... If it is over 13.8 volts--Then the battery is being over charged and will will fail sooner.

Many (inexpensive) battery maintainers do not have a "real" float voltage stage.

For deep cycle batteries, they do like to be cycled once a month or so to 75% SoC or a bit less, for longer life (common knowledge--Which could be right or wrong).

If not a sealed battery, check the electrolyte every month... If you have to refill too often (less than 1-2 months between refills), then the float voltage many be too high.

-Bill

Sitesure · January 2019

This one is supposed to manage the float... but good point, I'll check periodically, thanks.

Pump won't start on power from Inverter

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