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A question that someone may be able to answer easily, I just don't understand the basics well enough.
I'm in Nicaragua atm at my brothers and we've just had a power cut. This happens frequently where he lives.
He has a small solar install with 2x110Ahr 12V lead acid batteries charged by the solar panel feeding 24v into an inverter.
The inverter is labelled as HZSolar 1500w pure sine inverter (3000w peak).
He's been able to run a drill marked as 1000w off the inverter.
When he tries running a water pump off the inverter an overload alarm fires along with a warning light.
The water pump is the smallest one from this <
i.e. the 3.5A/127V model.
The water pump works fine on mains and two pumps have been tried, same outcome.
Naively the pump is 3.5a @127v which to my mind should be well within the capabilities of the system. I suppose that there will be a spike on startup but would this be any worse than a drill?
Any suggestions as to why the water pump cannot run off the inverter and what he would need to do to remedy this?
Is the pump trying to start under load? Have you tried it starting empty? If it's self-priming, does he need it to cut in and out automatically (e,g, on a press.sw. or level sw.), or can he start it empty, then let it prime when running? Not ideal to run it dry for a few seconds, but may be a solution.
The pump is connected inline from a watertank to the house. It pumps the water up one floor. It switches on automatically when the pressure goes below a threshold.
Currently it runs fine on mains supply but he wants it to run off the inverter due to the frequent power cuts.
The pump does not start at all when run off the inverter. The inverter sounds an alarm and shows an error message.
The startup current draw will be at least 6 times the nominal current. That will be what is tripping the inverter
Meaning that he needs a bigger inverter?
The one he has currently is 1500W / 3000W peak. At 3.5ax127v he should be (just) inside the peak rating. Would adding more batteries likely help or is a bigger inverter going to be required?
Why not a 12v pump negating the inverter ? Look at seaflo .
Depending on what he's using the water for of course..
Bigger inverter might fix. A single-phase motor has a giant capacitor inline with one of the windings which is the cause of your problem.
Other options would be to change to a 240v inverter and pump, or look at installing a single-phase soft start module on the pump (it must be marketed as suitable for single phase or you’ll knacker them both).
Has to be a local pump - European parts are not available locally and repair of non-commonly used parts is prohibitively expensive here.
Would adding more batteries likely help or is a bigger inverter going to be required
It's difficult to know really. You are right at the limit of the inverter so the other suggestions of a soft start might help. I would measure the battery voltage while you start to run the motor to see what it is doing. You might be just within the range of the inverter with good batteries but outside if the batteries aren't good enough any more. There isn't an obvious answer here really
The batteries are pretty new so I assume good. The pump was tried when the batteries were brand new with exactly the same behaviour.
I'll get him to try measuring the voltage on startup. Adding 2 note batteries is the cheapest solution here. A bigger inverter is massively expensive here. He may have to import a soft start module, again potentially 2x - 4x cost depending on what customs decide.
I’m wondering what the capability of the inverter is for VArs - the starting current of 5 or 6 times the 3.5A @127V running current is not 2.2-2.7kW - much of the kVA will be KVAr.
Of course it’s VAr output might be fine.