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I'm changing out the pump for a pond and I am looking for an objective set of eyes to either confirm that my idea will work or to tell me it won't and why. I've attached a diagram to help explain things.

The new pump (I) is rated 12V 10A and indicates 16A maximum, which I take to mean that when starting up it may/will draw up to 16A. (The old pump was rated for 12/24V and was submersible but didn't work well.)

The pump (I) will be switched on for a period of time (about 10-12 minutes) per hour to pull 100-150 gallons of dirty water from the pond where dirty bits are separated out from the water and then clean(er) water is returned to the pond via gravity.

To handle the scheduling of the pump I am (initially) planning to use an Arduino (D) and a relay (E) to control power to the pump. A sketch in the Arduino will handle signalling the relay.

I've got a Fuse Block (B) that I'm using to also split up the circuit and independently power the electronic bits and the pump.

The pump isn't rated for 24V so I need to step the voltage down to 12V and that is handled by a pair of DC-DC converters that take 24V and output 12V 10A each. (F and G)

My intention at (H) is to take the two 12V 10A lines and tie them together to give me enough amps for the 16A max that the pump may want. I think if I only use one of those converters (F or G) then I'm not going to have enough amperage when it starts up.

Intuitively this makes sense to me but I'm not an electrical engineer so I'd appreciate some feedback on this. I am waiting on some parts so I have wired this all up yet.

Diagram

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    \$\begingroup\$ In general, you can't simply connect the outputs of two converters directly in parallel like that -- unless they're specifically designed for it, in which case there will be documentation showing exactly how to do it. Sometimes extra wire(s) between the converters are required. \$\endgroup\$
    – Dave Tweed
    Aug 7 '20 at 20:33
  • \$\begingroup\$ If the battery bank could be reconfigured as 12V OR the pump could run from 24V, it would save you quite a bit of hassle. \$\endgroup\$
    – mkeith
    Aug 7 '20 at 20:35
  • \$\begingroup\$ When the pump turns on or Off and there is a large electromagnetic pulse the solenoid action of a large area can cause the Arduino to disfunction. Thus use twisted pairs thruout for switched power and signals. \$\endgroup\$ Aug 7 '20 at 20:36
  • \$\begingroup\$ It would be better to use a pump matched to the battery voltage then use a float charger of equal power. Then use an automated timer outlet to connect the pump with an RC power snubber for arc suppression on disconnect. Relays are derated 50% or so for pumps due to arc inertia or back EMF \$\endgroup\$ Aug 7 '20 at 20:40
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    \$\begingroup\$ @KyleB No worries - I'm glad to get such a good response. Appreciate all the info! \$\endgroup\$
    – itsmatt
    Aug 7 '20 at 23:20
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If those converters have a built-in 10A constant-current limit they will share the load, if not they will quit one after the other.

the 10A fuse is too small. use thicker wire and a larger fuse and a 20A or larger relay.

with only 20A available the pump will be slow to start.

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if 24vdc battery and all components are isolated from other items running on the battery (chassis ground isolation, especially), you can place a secondary, parallel wiring configuration for 12vdc in addition to the series 24vdc configuration. then you have 12vdc for the pump, high current, and 24vdc higher voltage for other loads on the battery

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