The (30) solenoid valves are 12v, all identical, each controlled by a relay and are rated at 6.2 watts of power consumption.
They will all be turned on simultaneously and turned off separately. This will happen frequently, once every few seconds. The battery can be charged regularly.

What ah of battery is required? Deep cycle? Also what is the calculation? (so as to work out variations)

Thanks very much in advance

  • \$\begingroup\$ You have omitted how long you need it to actually run off said battery which leaves the battery's amp-hours rating open to anything between zero and infinite. \$\endgroup\$ – DKNguyen Sep 24 '19 at 19:17
  • \$\begingroup\$ Can you? Yes, if you choose an appropriate battery. \$\endgroup\$ – Hearth Sep 24 '19 at 19:21
  • \$\begingroup\$ How long will the solenoids remain on? Based on your specification, it looks like each solenoid will draw ~520mA, which means your battery should be able to supply at least 20A (added some margin). \$\endgroup\$ – Caleb Reister Sep 24 '19 at 19:21
  • 1
    \$\begingroup\$ A few tips: we don't usually say "watts of power consumption" in the same way we don't say "kilometers per hour of speed". We can just say "watts" or "kph" or "power consumption of xx watts" and "speed of xx kph". Also, SI units named after a person have their symbols capitalised and are lowercase when spelled out. V / volt, A / amp, K / kelvin (and 'k' for kilo), etc. \$\endgroup\$ – Transistor Sep 24 '19 at 19:27
  • \$\begingroup\$ The solenoids may have a high "inrush" current requirement, so you may have to double your calculated "steady state" battery requirements (and wire). It would help if you had a data sheet for the solenoids to look at. \$\endgroup\$ – Ron Beyer Sep 24 '19 at 19:32

Assumiung the average (mean) number of solenoids on over time is 15, the average current draw will be 7.6A

so for 1 hour between charges you need at-least a 7.8Ah or larger battery. for 2 hours get at-least twice that etc...

But get a much larger battery like 12Ah or more for 1 hour, the extra headroom results in a much longer battery life (longer time before you need to replace the battery because it's worn out and can't hold enough chgarge)

the calculation is you take the current needed by the solenoid 6.2W at 12V is 6.2/12 = 0.52A, multipy that bt 15 for average 15 solenoids 7.8A

then you multiply that by the number of hours between recharges to get the battery capacity needed 7.8A times 1 hour is 7.8Ah

then you increase that a bit for reliability and choose a battery size that's suitable.

  • \$\begingroup\$ Thankyou for your answer. Exactly what i was after! \$\endgroup\$ – enginology Sep 25 '19 at 8:22

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