Protecting 24V control signals?

[fafrd]

I’m using my 24V battery to supply the 24V control signals to drive a couple SSRs and looking for the easiest way to protect that wire.

Since the currents are minuscule, I’m thinking I can just use a 1A or 2A inline-fuse like this:

https://www.amazon.com/dp/B0C7CJ16LT/ref=sspa_mw_detail_1?ie=UTF8&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams&th=1

Just thought I’d check with in case anyone has a better solution or I’m missing some issue with using a simple inline fuse for this need.

 

[HarryN]

Are you planning to have an in line fuse like that attached directly to a large battery bank that can output lots of amps?

That is usually the main discussion point around fusing - can it block the current in an actual short or is the arc going to be so strong it just keeps going?

( amps interrupt current )

The good news is that that cylindrical fuses are available in quite high protection levels.

The particular one that you listed has an AC voltage rating but not a DC voltage rating if that is important to you.

Digikey sells much better quality fuse holders and fuses including ceramic ones that won't arc flash open if you are into that kind of thing.

__________

In the mobile / marine world they use a series of protections, for instance for connections directly to a large DC source ( battery pack) there is a fuse or breaker with a large amp interrupt current rating, and then down stream they use smaller fuse blocks for small currents like you have.

 

[fafrd]

Are you planning to have an in line fuse like that attached directly to a large battery bank that can output lots of amps?

No, I was planning to connect the ‘control signal’ source on the far side of the battery fuse. But the battery fuse is rated for too much amperage to protect the small wires I am using to control SRRs.

That is usually the main discussion point around fusing - can it block the current in an actual short or is the arc going to be so strong it just keeps going?

The control currents for the SCCs is measured in 10s of mA, so even a 1A inline fuse is overkill for this application.

( amps interrupt current )

The good news is that that cylindrical fuses are available in quite high protection levels.

The particular one that you listed has an AC voltage rating but not a DC voltage rating if that is important to you.

Good catch - thanks. The blade-type fuses are rated for DC (and also come with inline housings) so if I can’t find DC-rated cylindrical type, I’ll switch to blade-type:

https://www.amazon.com/dp/B07Q9PL4R6/ref=sspa_mw_detail_0?ie=UTF8&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams

Digikey sells much better quality fuse holders and fuses including ceramic ones that won't arc flash open if you are into that kind of thing.

The probability of an SSR shorting is vanishingly small. So I’m into protecting the small control wires as inexpensively as possible (while still being safe).

__________

In the mobile / marine world they use a series of protections, for instance for connections directly to a large DC source ( battery pack) there is a fuse or breaker with a large amp interrupt current rating, and then down stream they use smaller fuse blocks for small currents like you have.

Yes, that’s exactly how I’m planning to wire it up. I can use one fuse for all control signals since I don’t care if the whole system shuts down if there is a failure…

Thanks for reminding me to make sure I’m getting fuses rated for 29VDC…

 

[AntronX]

I use 250Vac rated Buss AGC glass fuses with my 44Vdc battery for powering low amperage loads. Had one fuse blow already and it stopped the arc no problem.

 

[efficientPV]

I bought a bunch of glass bead one piece inline fuses with leads and chose 3A as a size that will protect wire and inside of electronics. I solder them to the section of wire and put heat shrink over them. No need to take up panel space unless you like that sort of thing. Similar to these

200Pcs Glass Fuse Tube Axial With Lead Wire Fast Blows Fuse 3x10mm 250V/2A | eBay

Fuse Type: Fast Blows Fuse. For: Circuit Protection. Type: Glass Fuses Tube. Glass Tube Size: 3mm 10mm. Shape: Pointed Tube. Color: Silver. I send goods within 12 hours. Usually I will respond in 24 hours.

www.ebay.com

 

[fafrd]

I use 250Vac rated Buss AGC glass fuses with my 44Vdc battery for powering low amperage loads. Had one fuse blow already and it stopped the arc no problem.

Thanks. Amy reason you chose a VAC fuse for a VDC source?

 

[fafrd]

I bought a bunch of glass bead one piece inline fuses with leads and chose 3A as a size that will protect wire and inside of electronics. I solder them to the section of wire and put heat shrink over them. No need to take up panel space unless you like that sort of thing.

Not taking up panel space for something that’s never going to happen unless there is a failure is my goal.

Similar to these

200Pcs Glass Fuse Tube Axial With Lead Wire Fast Blows Fuse 3x10mm 250V/2A | eBay

Fuse Type: Fast Blows Fuse. For: Circuit Protection. Type: Glass Fuses Tube. Glass Tube Size: 3mm 10mm. Shape: Pointed Tube. Color: Silver. I send goods within 12 hours. Usually I will respond in 24 hours.

www.ebay.com

Soldering the fuse to the wire is an interesting idea. More of a PITA to replace but since it’s never going to happen, worth considering.

Thanks.

 

[AntronX]

Thanks. Amy reason you chose a VAC fuse for a VDC source?

Cheap price.

 

[fafrd]

Cheap price.

I suppose 120VAC fuses rated for ‘X’ Amps will blow from less than ‘X’ amps of DC current, so is there some ‘rule of thumb’ for sizing an AC fuse for DC current?

I’ve got such low current levels (<100mA DC) I’m thinking the smallest fuse I can find is likely to suffice…

 

[AntronX]

I suppose 120VAC fuses rated for ‘X’ Amps will blow from less than ‘X’ amps of DC current, so is there some ‘rule of thumb’ for sizing an AC fuse for DC current?

I’ve got such low current levels (<100mA DC) I’m thinking the smallest fuse I can find is likely to suffice…

Same blowing current as AC rating but the issue is DC fault current interruption rating which AC type fuses are not designer or rated for. In this case going with physically longer fuse is better to give a better chance of extinguishing an arc.

 

[MyK3y]

Have you looked at optical isolators? It’s what I use on things like CNC plasma cutters where stray amps can easily fry delicate electronics

They can also step-down, should you need it to.