Device used AC power supply, modifying circuit for DC - Fuse question

[Mishael]

24 V nominal would be the usual supply to run a 24 V relay from, because even with a tolerance of +/- 20%, and some voltage drops, the voltage would always be over 18 V

I had never really thought about this, but I am starting to understand now. My experience with low voltage relays and the capacity of a transformer is primarily in AC environments where all of the figuring is done on paper using the manufacturer specs. relay/contactor hold VA * quantity ≤ XF VA * 0.8
Ive never had to factor in whether my voltage would be sufficient because I always oversize the XF by as much as is cost effective

People tend to look at AC and DC the same. e.g. 24 VAC and 24 VDC. They are not

This is where my plan started to go off the rails

That depends on your particular point of view - the whole idea of specifying as RMS means they ARE the same - for many purposes, such as heating and lighting. It's really an 'electrical' specification rather than an 'electronic' one.

A great summation of the source of my confusion. my electrical experience is much greater than my electronic experience. While the basic idea of both is the same, there are vastly different principals and practices between them

Attached is the updated schematic as I have the board now.

 

[Nigel Goodwin]

Interesting circuit, quite sneaky using thyristors to latch the relays on, and transistors to turn them off again.

However, it's VERY old technology - and would be much simpler these days using a microcontroller

 

[Mishael]

However, it's VERY old technology - and would be much simpler these days using a microcontroller

The unit I have been working on is likely from the early 90s and it is the oldest version of this product I have come across, however this was an industry standard device for installed sound systems up until at least the early 2000s because of their reliability and performance. Even now, there is not one quite like it. Most sequencers available now have 3 outputs with a few offering 4, and I have found one offering 6 circuits/outputs (the outputs are 48V, it costs over $1000, and it is basically its own subpanel) but none of them have 6 sequenced SPDT contacts in addition to 6 power outputs for relays.

I find that I like a lot of the older audio equipment I install better than some of the new stuff. The cost to feature ratio seemed a lot more linear and since all devices will fail at some point, the fact that the older equipment can be repaired is a huge determining factor in what is purchased for a lot of the places I work

 

[Nigel Goodwin]

The unit I have been working on is likely from the early 90s and it is the oldest version of this product I have come across, however this was an industry standard device for installed sound systems up until at least the early 2000s because of their reliability and performance. Even now, there is not one quite like it. Most sequencers available now have 3 outputs with a few offering 4, and I have found one offering 6 circuits/outputs (the outputs are 48V, it costs over $1000, and it is basically its own subpanel) but none of them have 6 sequenced SPDT contacts in addition to 6 power outputs for relays.

I find that I like a lot of the older audio equipment I install better than some of the new stuff. The cost to feature ratio seemed a lot more linear and since all devices will fail at some point, the fact that the older equipment can be repaired is a huge determining factor in what is purchased for a lot of the places I work

It's a very simple device, and cheap and easy to make one using a micro-controller - just a micro-controller, relays, drivers for the relays, and whatever controls you wanted (like a pot for the speed, or buttons up and down, and some kind of display is desired).

Dead simple to do with an Arduino (or anything else), plus one of these relay boards - up to 8 channels done for less than £10.

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Biggest cost would be a box and connectors for it.