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I need help designing the power distribution system for a rocket test stand. I am new to power electronics so I am confused about how to go about it.

I have to supply power to 8 solenoid valves that require 24V and 4A to actuate. I am planning to use two 14.8 V Li-Po batteries to supply power to each of the valves. So I need to be able to step down 29.6 V to 24 V.

Where I am confused is should I have 8 separate step-down converters that will convert 29.6-24 V and 4A of current , or should I have a single step down converter that converts 29.6-24V but supplies 32A of current that will be split into eight 4A current to each valve when connected in parallel.

I have little experience with this, so any help is appreciated!

Link to Solenoid: https://clarkcooper.com/hpv/EH70.html#HiPresstabs=2 Link to battery: https://hobbyking.com/en_us/turnigy-high-capacity-battery-20000mah-4s-12c-drone-lipo-pack-xt90.html

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  • \$\begingroup\$ Will these solenoids ever be actuated at the same time? How many could be activated at the same time? Please provide links to the manufacturer's datasheets for the solenoids and for the batteries. \$\endgroup\$ Nov 9 '19 at 19:05
  • \$\begingroup\$ @ElliotAlderson They will open approximately at the same time because the test-fire only lasts 8 seconds, so the opening of the valves will have very little time difference \$\endgroup\$ Nov 9 '19 at 19:31
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I guess 4 A step-down converters are easier to come by than 32 A converters. Here are some other observations:

Each Li-Po cell is 3.7 V only when half-charged. The full range is 4.2-3.3V, thus a 4-cell battery like the one you linked will give up to 16.8 V, not 14.8 V. You could use a single 8-cell Li-Po instead of two 4-cell, but Hobbyking only lists a single 8-cell model so they might be less common.

You could use even fewer or even a single battery to power all solenoids to cut down on complexity/costs. I don't think the current is too high, especially not for a short burst of power. Keeping track of the charge of 8 or 16 batteries would be a risk, not to mention a lot of work. The batteries will degrade if stored at full charge, so just putting them into storage and preparing them again would be some work.

On the other hand, perhaps you're looking for redundancy. Consider what happens if one valve fails versus if the whole solution fails. You would have an easier time adding separate redundancy if your primary solution only has one 8-cell battery.

Another thing to watch out for is back EMF when shutting off the solenoids. I image the resulting voltage spikes can be massive if there's no protection.

Sounds like fun!

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