Electrical experts (including arm chair types)

It could be done with a single 230VAC to 12VDC supply, but it may be cheaper to use multiple.

Will all three pumps be running at the same time?
I'd doubt they'd draw the full 17A, so you might get away with a lower rated power supply, but without knowing details, it's hard to give any definitive answers.

The pumps are only 250watt rated, but they say they potentially draw between 17 and 21ahr.  They possibly need to run in parrallel .  I've seen you can get a 750w ac/dc converter rated at 60amps so could connect all to that device -but i wonder, if as you say is it better to run 230v to the pumps through the converter, or, convert it at source. - Source will be 10-15 meters away.  Environemnt could be damp conditions, hence thinking it's best o convet close to source of power vs where it is needed.

Forgot to clarify, that in theory you'd need a supply capable of 17Ax3 (51A), but that depends on the likelihood of all three pumps running at full load at the same time, hence asking about what they actually are.

Depending on power supply requirements, you might three ~240W PSUs cheaper than a single 750W PSU, but size/space constraints can dictate what you need to use.
Also depending on the pumps, you might need to oversize the PSU, as some motors can have quite a high start up current

thanks MC, i get what you are saying and i was looking at the differnece between single units at a lower ahr or just one higher one that i can "tee" off the 3 pumps to - a bit like this on amazon

.amazon.co.uk/Version-Converter-Switching-Transformer-Security/dp/B0F4DNWVSK/ref=asc_df_B0F4DNWVSK?mcid=22cd623b1bc93ce484a5f6036e18819a&hvocijid=15786825913664262351-B0F4DNWVSK-&hvexpln=74&tag=googshopuk-21&linkCode=df0&hvadid=696285193871&hvpos=&hvnetw=g&hvrand=15786825913664262351&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045852&hvtargid=pla-2281435176618&gad_source=1&th=1

Pedant Mode
It's just A, as in Ampere, not ahr!
(AHr is Amp Hour, which is a battery capacity measurement)
End Pedant Mode

A lot will come down to installation preferences and cost.
20A rated cable is going to add to cost, 60A even more so, especially if you want decent quality flexible cable.
Off the top of my head, you'll need at least 2.5mm2 for 20A, and 6mm2 for 60A, but check those sizes.

On the flip side, some standard Artic flex to extend the 230VAC where you want it will be cheaper, but then you need to waterproof the PSU. The convenience of not having as long runs of heavy cable to deal with may make this option more appealing.

Or if the pumps won't run continuously, you could add a 12V battery and big battery charger, as that way you don't need permanent mains.

Or just use 230VAC pumps, as water proof sockets and an RCD isn't that expensive.

As with a lot of seemingly simple installations, it's the finer details that can add a lot of cost, and get you stuck in option paralysis.

Posted by: mc

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Off the top of my head, you'll need at least 2.5mm2 for 20A, and 6mm2 for 60A, but check those sizes.

I think you're an order of magnitude out (assuming the 15m above is how far the cables have to go)

Posted by: Aidy

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Posted by: mc

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Off the top of my head, you'll need at least 2.5mm2 for 20A, and 6mm2 for 60A, but check those sizes.

I think you're an order of magnitude out (assuming the 15m above is how far the cables have to go)

Not that far out, depending on the cable.
2.5mm automotive thinwall is good for 29A, and 6mm for 50A.
However that is thinwall cable pushed to it's limit, so you'd probably want to upsize given the distances involved, and if it's going to be enclosed.

But automotive thinwall isn't exactly flexible, so if this isn't for a (semi)permanent install, I'd be looking for something more flexible, which given the sizes involved, will bump the price up quite a bit, as flexible cables in those sizes are not as common (aka more expensive!)

In short it sounds like you want something like a single 750W 12VDC supply, or a 230V spur/ring with 3 250W supplies, with 2.5mm2 for each pump on the 12V side, whereas the 230VAC can be much smaller, perhaps 0.75mm2. In reality, the cheapest/best setup is going to be dictated by layout/cable run length and meeting wiring regulations for protection, earthing etc. 

pedant mode

A = Amperes = Current = how many electrons are being pushed through the wire
Ahr = Amp-Hours = Electric charge, not exclusively for battery capacity
W = Watts = Real Power, work utilised/consumed
VA = Volt-Ampers = Apparant power (including reactive), total load

Wires are sized based on Amps with correction factors applied for the installed environment/voltage etc.

Transformers are sized based on VA - you need to factor in the power factor to account for the total load, including reactive power that bounces around without doing real work. However, AC to DC power supplies tend to keep it real and are just specified in Watts.

thanks all, for the input.  Im not overly worried about cost at this point, its more a safety aspect.  I want to keep 12V as the pumps have already been enclosed in a "rig" that has a 12V battery "space" -so we know it works well.  However, as we will be in an environment that may be continously wet  and dirty, and in constant operation i wanted to limit the voltage going to the areas where the pumps are situated.  Im quite happy to look at enclosing 1,3, or more inverters into a weatherproof box and run tails out, do you know if you can get the equivelant of the 3 pin bullet connectors but for 12V cable?  Oversizing the cable is a good idea, and again not something that concerns me from a cost perspective.

Generally called a power supply, inverter is for DC to AC. If you're putting in a weatherproof enclosure you do need to think about ventilation/heat management and potentially oversizing the supply.

You can use higher voltage rating connectors for 12V but I'd recommend looking at automotive 3-way electrical connectors with whatever IP rating is appropriate for your install. E.g. Delphi 'weather-pack'.