Bank of MANY 12v relays

jantman

I usually don't post two questions so quickly in succession, but I'm working on pricing out this project....

A separate system from the Ammeter post...

I'm looking to setup a system with many control relays, all 12v and about 40A.

The end product....

A control panel for various 12v accessories, mainly lighting, on a vehicle. Relays will need to control 12v/40A loads. There will be an array of momentary push buttons, each controlling a different load. The buttons will have LEDs, but the LEDs will be on the load side of the relay, and therefore not an issue.

The questions I have -

1) There will be about twenty or 25 loads, and therefore about 23-28 switches. Each load will have its own switch, plus one switch to control all loads, and two others to control a certain group of loads. Each of the latter three will be programmed with a sequencer to spread out the inrush to the system. What is the best (and most economical) way to build a system which will control, say, 25 different 12v automotive relays?

2) I assue that both sides (input and output) will end up using D/A's. Is there any issue with having ALL 25 loads powered on at once?

Thanks,
Jason Antman

Newzed

How much current does the relay coil draw?

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Jonathan

Jason,

I'm assuming the switches for the relays are not momentary types, i.e. they are regular switches that remanin on until you turn them off.

You can use an input shift register to poll the state of the inputs. Since you can cascade these devices, you can have as many inputs·as you need for the cost of 4 I/O pins.

For the outputs I *think* you can use an output shift register to drive transistors or FETs to drive the relays. Maybe someone who has tried this can chime in, I never have.

Jonathan

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