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[Entwood]

I'd have thought the co-ax core would act like a rather large fuse and simply blow at 500 amps !! even for only 12V for 20ms that's one hell of a lot of energy .. some welders produce less !!

[Gaffers]

I'd have thought the co-ax core would act like a rather large fuse and simply blow at 500 amps !! even for only 12V for 20ms that's one hell of a lot of energy .. some welders produce less !!

You obviously havent seen the energy readout on a rapid car charger.  At peak I saw 395V and 125A   From that point on I made a conscious decision to never sit inside while it is charging on a Rapid.

[Kevin Wood]

It does rather depend what type of coax we're talking about. The radio contest group of which I am a member uses this : http://www.rfparts.com/old_site/heliax_LDF550A.html.

It's affectionately known as "donkey's dork", due to the fun and games involved in unrolling it and wrestling it off the ground and up a 100' lattice tower.

I don't think you'd "blow" that in a hurry.

[Yasmine Lee]

The biggest relay I have found is 100amp which I used in a home made split charge system on my camper van.

I have fitted 200amp ones in my split charge systems in my mobile workshop

http://www.ebay.co.uk/itm/12-VOLT-200-AMP-HEAVY-DUTY-MAKE-BREAK-WINCH-CAMPER-SPLIT-CHARGE-RELAY-/321101707045?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4ac3273725

or you could try

http://www.ebay.co.uk/itm/500-amp-MEGA-FUSE-12v-24v-32v-500a-500-Brown-We-stock-All-Sizes-and-Fuse-Holder-/121208863346?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c389c7a72

[Kevin Wood]

Hang on. I've had a great idea. Guffer... When is your milk float available for some "experimentation"?

[Gaffers]

Hang on. I've had a great idea. Guffer... When is your milk float available for some "experimentation"?

Ferk o.... ...erm....no 

[Entwood]

I'd have thought the co-ax core would act like a rather large fuse and simply blow at 500 amps !! even for only 12V for 20ms that's one hell of a lot of energy .. some welders produce less !!

You obviously havent seen the energy readout on a rapid car charger.  At peak I saw 395V and 125A   From that point on I made a conscious decision to never sit inside while it is charging on a Rapid.

Cables are a tad thicker than co-ax last time I saw a milkfloat being refilled ... 

I'm well used to high power circuits .. an aircraft external power cart gives 40KVA at 115 v and 400 cps at 3 phase ... but the cables are about an inch thick for each phase plus another the same size for the 0v line... slightly bigger than co-ax ?? 

[TheBoy]

Or.. for a one-off, find a test house who have a facility for this type of testing and pay for the test instead of the hardware?

Not sure where you'd go, but there'll be someone who can do it, I'm sure.

In effect, this is what he does.  I've given the simplistic view of what he needs to achieve to see if the coax will survive the high currents, and due to low budgets (education), hopefully portrayed the need to do the initial tests with low cost, off the shelf components. If things are looking positive, budgets can be applied for, and a bucketload of 1kA thyristers, or industrial power switches can be bought.

And the capacitors needed, they are friggin expensive, and they need a roomful. For now, he's hoping a big car battery will be able to deliver the current needed for the test.


I don't begin to understand half the stuff he has to do, but I know it is researching beyond the limits of what we currently know about physics. Hence, he has stuff in deep mines helping search for pesky particles, and this experiment is to create magnets so powerful that it can affect matter at the atomic level.

[zirk]

Why coax out of interest?, the Andrews LDF stuff that Kevin mentioned is good gear, for RF, the smaller spec, 250, 450 is solid inner core, cant remember about 550 as not used it for a while, but once you go 750 or above the core isnt solid, its hollow, as a cost and wieght saving, at RF levels makes no difference as it more about keeping the inner and outer dielectric size the same for impedeance reasons, the point beng it probably no good going for a higher spec RF cable for proper DC / AC current drains.

[Kevin Wood]

Or.. for a one-off, find a test house who have a facility for this type of testing and pay for the test instead of the hardware?

Not sure where you'd go, but there'll be someone who can do it, I'm sure.

In effect, this is what he does.  I've given the simplistic view of what he needs to achieve to see if the coax will survive the high currents, and due to low budgets (education), hopefully portrayed the need to do the initial tests with low cost, off the shelf components. If things are looking positive, budgets can be applied for, and a bucketload of 1kA thyristers, or industrial power switches can be bought.

And the capacitors needed, they are friggin expensive, and they need a roomful. For now, he's hoping a big car battery will be able to deliver the current needed for the test.


I don't begin to understand half the stuff he has to do, but I know it is researching beyond the limits of what we currently know about physics. Hence, he has stuff in deep mines helping search for pesky particles, and this experiment is to create magnets so powerful that it can affect matter at the atomic level.

OK, so if capacitors are out, you need to produce an accurate pulse, which means solid state switching. In some respects, you are in a similar situation with the switching devices as with the cable, in predicting what will survive. I wouldn't mind betting that a parallel combination of cheap MOSFETs would work at low voltage. They are normally limited by junction temperature rather than rated current for short pulses, so you need to calculate how much that pulse will heat up the junction, and parallel devices as required. At a couple of quid a go, you can afford to use a few. The downside is that you need to ensure that current is shared between the devices reasonably equally, and the gate capacitance goes up, meaning you need a better driver to switch them quickly. Switching speed is key to avoiding heat dissipation in the switching devices, of course.

Your current will also be limited by resistance, so at 12V you'd only be able to test a very short length of cable, and need to be able to pretty much bolt your circuit onto the battery terminals.

[Kevin Wood]

IIRC, LDF-550 is hollow cored, but my point is that it'd survive a lot more than what most people think of when coax is mentioned (i.e. the stuff hanging out the back of your TV).

[zirk]

Im not dissagreing with you Kevin, its good gear, but at near DC levels solid core is better at current than hollow. Possible another issue would be how long does it need to be, on the bigger Tramsmiter Site, talking BBC, IBA type, long lengths of Coax are pressurised by Gas or Air by a pressure pump, as so to keep moisture, temp at bay, so if long lengths are involved here, what effect would that have on the 'so called texting'?

[Kevin Wood]

Im not dissagreing with you Kevin, its good gear, but at near DC levels solid core is better at current than hollow. Possible another issue would be how long does it need to be, on the bigger Tramsmiter Site, talking BBC, IBA type, long lengths of Coax are pressurised by Gas or Air by a pressure pump, as so to keep moisture, temp at bay, so if long lengths are involved here, what effect would that have on the 'so called texting'?

Yep, all agreed. 

[Marks DTM Calib]

Or.. for a one-off, find a test house who have a facility for this type of testing and pay for the test instead of the hardware?

Not sure where you'd go, but there'll be someone who can do it, I'm sure.

In effect, this is what he does.  I've given the simplistic view of what he needs to achieve to see if the coax will survive the high currents, and due to low budgets (education), hopefully portrayed the need to do the initial tests with low cost, off the shelf components. If things are looking positive, budgets can be applied for, and a bucketload of 1kA thyristers, or industrial power switches can be bought.

And the capacitors needed, they are friggin expensive, and they need a roomful. For now, he's hoping a big car battery will be able to deliver the current needed for the test.


I don't begin to understand half the stuff he has to do, but I know it is researching beyond the limits of what we currently know about physics. Hence, he has stuff in deep mines helping search for pesky particles, and this experiment is to create magnets so powerful that it can affect matter at the atomic level.

Right, I am now confident that he/they are out of thier depth....big time.

20mS through a mechanical contact....no chance and certainly not at the currents talked about.

Thyristors.....nope, as you cant turn them off.

As for will the coax take it, yes it may well.

Yes the losses are such that the core will get hot but if the duration is short enough then it wont have heated to the point of failure in the short time.

The bigger concern would be the connectors.

[Marks DTM Calib]

This experiment is to create magnets so powerful that it can affect matter at the atomic level.

Thats already done, pop down your local hospital for a demo.