I have a 12v 14 amp pump for removing water from a boat. I normally run from the engine alternator but that's out of commission at the moment. I have a 12v 30 amp LED transformer (240VAC input) but I know the pump motor will draw significantly more current at start up and this will probably fry the transformer as I don't think it's designed for inductive loads. I've read that a PTC thermistor might do the trick but would like some tips on how to specify this component.

This is the transformer I have https://www.amazon.co.uk/dp/B082TTY3L7

 

That's not a "Transformer",
that's a SMPS ( Switch-Mode-Power-Supply ).

The SMPS will protect itself from excessive Current on start-up.

The "~14-Amp" rating is a "nominal" rating, and will probably be slightly less
considering that it is designed to work with Voltages up to roughly ~15-Volts,
and You will be supplying a Regulated ~12-Volts.

The best plan would be to insure that the "New" Battery in the Boat is fully charged,
and is connected to a stout, "Automatic" Electronic-Battery-Charger,
which is left plugged-in continuously.

Your SMPS will not serve as a Battery-Charger.
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You are correct to be worried. Starting amps for an electric motor can be 7 times higher than the run amps. That 14A motor could easily require 100A to start the motor.

Most switching power supplies use a hick-up or interrupt overcurrent protection that turn themselves off if you draw more than rated current. When they interrupt you have to power the supply down and back up before they will output power. Obviously these are not going to work with a motor unless the power supply is grossly oversized (12V @ 100A) for the load.

What you want is a supply that will operate in a constant current mode when overloaded. That way it will deliver as much current as it can while starting the motor and then resume normal operation in run mode.

The LED supply you listed is a constant current supply, but I wouldn't trust it as far as I could throw it. I suggest you look at a MeanWell supply like one of these that will actually deliver the rated power and has the required constant current overload mode:

https://www.meanwell.com/webapp/product/search.aspx?prod=RSP-320
https://www.meanwell.com/webapp/product/search.aspx?prod=RSP-500

The Meanwell RSP-320 costs ~$60 and is rated for 12V @ 26.7A. The RSP-500 might be a better choice for you since it puts out 12V @ 41A, but it costs about $110. My guess is that the RSP-320 will do the job. Buy it from some place you can return in case you need to use the RSP-500 instead.

A quality supply like a MeanWell is not nearly as likely to let the magic smoke out or kill you. These supplies are for indoor use only so I would mount this somewhere it can't get wet. If this is not practical (you did mention a boat), then I would put it in a watertight NEMA 4X enclosure.

-Edit- You can adjust the output voltage +/-15%, I would turn the voltage up to 13.8V since that is what the alternator is putting out when the engine is running.

 

I've read that a PTC thermistor might do the trick but would like some tips on how to specify this component.

The supply you have is constant-voltage (not constant-current) rated for 30A, so it may power your pump directly, but an inrush current-limiter (NTC) in series can be added for safety.
Edit: One of these, rated for 30A, with a 1Ω room temperature resistance, should work.

 

The Meanwell RSP-320 costs ~$60 and is rated for 12V @ 26.7A. The RSP-500 might be a better choice for you since it puts out 12V @ 41A, but it costs about $110. My guess is that the RSP-320 will do the job. Buy it from some place you can return in case you need to use the RSP-500 instead.

Thanks for the recommendation.

 

The supply you have is constant-voltage (not constant-current) rated for 30A, so it may power your pump directly, but an inrush current-limiter (NTC) in series can be added for safety.
Edit: One of these, rated for 30A, with a 1Ω room temperature resistance, should work.

Thanks for the details, especially the link to the thermistors

 

The best plan would be to insure that the "New" Battery in the Boat is fully charged,
and is connected to a stout, "Automatic" Electronic-Battery-Charger,
which is left plugged-in continuously.

A new battery is on the shopping list... but not this month. As I have a 16A 240v shore power supply a solution from the grid power would be nice while I'm in the marina and not out at sea.

 

Don't operate any Electronics in the Boat without a good, charged Battery properly installed.
The "Shore-Power-Supply" is an "unknown-source", and may be dirty and unregulated.
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