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Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 1138

Posted: 11:28pm 02 Oct 2024

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I have a number of projects coming up that require a relay switch that can switch a min of 200 amps at either 48 or 96v DC battery supply; normally I use those evac relays, readily available on eBay or AliExpress.

However some extra functionality is also required, such as smart switch capability, being able to turn off if the incoming voltage drops below limits and incorporate a pre-charge function when activated to charge up any huge capacitive loads prior to final switch closure. Seems easier to do all this on a single pcb using mosfets, costs work out way less than the evac relay.
Combined on resistance is about 0.0004r, so power lost at 200A will be 16watts, 100A = 4 watts, these higher currents will only be of short duration, so overall power lost\heating will be minimal.

Have used 5 mosfets to make a uni-directional switch, driven from an opto isolated 3 amp driver, the pre-charge mosfet also driven from an isolated voltage driver, switches a resistor for a short period. The main mosfets bolt to 40mm x 3mm alloy bars, for current capability, the bars protrude out the bottom of a plastic box.

CPU is a Picaxe 08M2LE to provide some voltage measurement and delay timing logic, an opto coupler input is used for switch activation, as the circuit is not that complex, I don't have a schematic drawing as yet, but will do one at some stage. PCB 105x148mm fits inside readily available low profile plastic cases.

PCB:

PM me if anyone wants the gerbers.

Cheers
Mike

Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 453

Posted: 07:28am 03 Oct 2024

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Looks good Mike, the only thing that would turn me off making one is the surface mount components. I don't like working with them myself.
Pete

Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 1138

Posted: 09:28am 03 Oct 2024

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Godoh said Looks good Mike, the only thing that would turn me off making one is the surface mount components. I don't like working with them myself.
Pete

Fair enough, you get used to using them, a lot of newer devices are not made in non-smd any more; don't think I would ever go back to using all through hole leaded components, find smd is cheaper, faster to assemble and makes for an easier design.

Cheers
Mike

rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 852

Posted: 11:34am 03 Oct 2024

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Solar Mike said I have a number of projects coming up that require a relay switch that can switch a min of 200 amps at either 48 or 96v DC battery supply; normally I use those evac relays, readily available on eBay or AliExpress.
Mike

Interesting project Mike, I will follow it with interest. Not sure I need all the smarts ... but a good reliable solid state switch could be very handy.

Godoh said Looks good Mike, the only thing that would turn me off making one is the surface mount components. I don't like working with them myself.
Pete

I thought I'd have to give up electronics when I started to see a lot of smd boards in for repair ... but after I tried driving a bus for a while I thought this is stupid ... electronics is a lot more fun.

I just hopped in and made it work. Sure, I work with my nose stuck to a magnifying lense ... but despite aging eyes, I find it easy. Sometimes I wonder what it would be like using a stereo microscope ... but haven't really felt the need to splash out on one.

It's cheap to buy a few kits of the various size and value resistors, caps, diodes, varistors ... so the bits are there if you need them ... and when I need smd IC's I just have to order any I don't have ... just like I do the through hole versions.

For me, there's no question ... it was just a mind set issue.

Cheers, Roger

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