What Fuses

[Jkulin]

"Hi All,

I wonder if you can help? I've made up a box with Bus Rails and a fusebox to bring all my 12v items into one central place, each having a separate fuse of 5A

The items running are: -

AZ-EQ6 GT Mount
7 Port USB Hub
Atik 383+ CCD Camera
Atik FW2 Filter Wheel
Moonlight Focuser with High Resolution Stepper Motor
Four Channel PWM Dew Controller, one input into the fusebox (Only 3 dew heater connected.
HP 17 Laptop, currently running on separate feed but last night it was running off batteries as I have yet to make a patch lead up for it yet

I'm using a Nevada PSW-30 Power Supply Which has a capacity of up to 30A http://www.nevadaradio.co.uk/amateur-radio/amateur-radio-power-supplies/nevada-psw-30h

The problem last night was that it was blowing fuses as soon as the mount started to slew to it's target, not the 5A fuses in the fuse box, but the 5A fuse in the cigarette adapter plug, now upon checking some of these fuses may have been 3.75A, so I would expect them to blow, but one was 5A.

Everything was working fine and has been working fine up to when I started to slew, the camera was drawing a bit with it's cool down stage to -15c

I don't want to put at risk any of the equipment, can anyone advise whether I should put the mount on a totally separate feed as the PSU does have two outputs.

The mount is working fine as I had to run the rest of the evening direct from a Tracer 22Ah Battery pack for the mount only.

Should I increase the Cigarette lighter plug to 10A and leave the new fusebox with 5A or 7.5A fuses in?

I'd appreciate any help, thanks.

[kbrown]

Maybe a bad power connection dropping the voltage a bit? 5A at 12V seems a little excessive (60W).

Looking at this video it should take about 3A max without load on slew at 12V and a lot less at 15V: https://www.youtube.com/watch?v=EYYwOn09tj8

Check the connections and maybe measure the power consumption if you have a multimeter capable of measuring 10A DC currents? Remember to connect it in series on the power line and not parallel!

 

// K

[Jkulin]

Thanks for your reply.

Will it make much difference when it is fully loaded up, last night it had about 10kgs on it plus the counterbalances?

T he connections are all new as I have made new waterproof ones up, one 12v input into the fusebox and up to 6 dedicated outputs

[kbrown]

I'm not 100% sure about your mount but at least my NEQ6 Pro doesn't show a big difference with or without loads. Stepper motors are usually current limited to a preset value so in theory the power consumption should be about the same. If the load is too high it just starts skipping steps.

[symmetal]

Is the cigarette plug connected between your fuse box and the mount? It may be the cigarette plug fuse is a quick blow type while the blade fuses are time delay or slow blow fuses and can tolerate high currents for a short period. Did you use the same cigarette plug cable when you used your tracer battery? The tracer may have been slightly lower voltage than the Nevada or thinner cable and it just coped.

Anything with motors should use slow blow fuses. With your fused distribution box there is no need for additional fuses in the leads to the mount.

Alan

[Jkulin]

Hi Alan, no everything is plugged via waterproof connectors into the box which then has 5A fuses in, then there is a master lead going from the box across my garden into the 30A PSU, the whole idea was to reduce the risk of injury by keeping all mains power safely in the shed.

I did wonder whether I should just connect the mains lead from the box direct into the PSU without any additional fuses as they are already fused and it is much easier to vary the fuse capacity as they use standard prong type car fuses.

I'm away in the morning for the weekend, so will set it all up again in my half way and doing some dummy runs, at least it will be warm and dry.

Thanks for your thoughts

[symmetal]

Hi John. From your last post it looks like the only cigarette plug used is the one plugged into your Nevada PSU. In which case the current for the whole of your rig is passing through the cigarette plug 5A fuse so it is quite likely to blow when your mount starts slewing. The dew heaters, camera and mount tracking along with the rest are probably taking around 4A and the extra 2 to 3A when your mount slews is exceeding its 5A capacity. The total current drawn is the sum of the individual currents.

The quickest way around this is to increase the fuse in the cigarette plug to 10A. Looking at your picture of the Nevada PSU there is no sign of where you can use its 30A, so I assume there are 30A terminal connections on the rear. You could connect your fused distribution box to these terminals and bypass the cigarette connector which should give you a more reliable connection. If you don't use cable rated at 30A for the lead from your PSU you would need to put an inline fuse of around 10A, or whatever the rating of the cable used is, in the positive lead from the 30A terminals. Using cable rated at 30A would give the benefit of less voltage drop at your distribution box. The fuse used at the PSU end, whether using the cigarette plug or the rear terminals is only there to protect the cable going to your distribution box and not the equipment attached to it. The fuses in your distribution box protect your equipment.

It looks like you have used 2 core mains cable as your current cable from the PSU. If this is 13A rated then a 10A fuse is fine at the PSU end.

Alan

[101nut]

One thing I would add is that I assume your 12V incomer is the orange lead? If so, I'd check voltages on full load at the bus bar as if that cable run is "across the garden" you are probably getting a significant voltage drop. I'd be using a larger cable ...

AndyG

[Jkulin]

Thanks Alan and Andy, sorry for the late reply. been away all weekend.

The cable I am currently running is about 40 odd feet from my shed is this: - http://r.ebay.com/5OuEb4 rated at 16.5A and is 1.00m2, they do offer a 25A cable which is 2.00mmm2 which I can order if you think it would be better?

The current configuration is/was: -

1. Cable connected directly to the rear connectors then to a female cigarette lighter, then my main cable with a male cigarette lighter adapter (5A fuse)plugged into that so it was interchangeable if I had to run from batteries if out in the field. From there the cable plugged direct onto the bus bars and then distributed into the fuse box with 5A feeds coming off for the peripherals. I'm not brilliant at electrics and just manage by. The only other fuses in the system is within the Nevada power unit which I presume is rated at 30A.

2. I then run a separate cable direct into the female cigarette socket that has a lower rated fuse (10A) so that could run the lighter peripherals, but again the male adapter had only a 5A fuse in.

I think from what you have all said is to run it direct from the rear connectors with a heavier cable direct into the fuse box and then rely on the individual fuses to protect the peripherals? Forgive me if I am repeating what you have both said, just trying to get it into my own head.

Andy I think you are right with the drop in voltage as from experience when the voltage drops the mounts make all sorts of weird noises and this was most definitely the case when I was blowing fuses, the Nevada unit pumps out 13.8V, so I assume that as you say the cable was not beefy enough and I was loosing over a volt at the mount.

So would I be better running one feed to power everything including the laptop or should I run one from the rear sockets and one for lighter duties from the female built in cigar socket.

I could make up a small fuse box with two heavier weight fuses with just two feeds coming out with a 30A fuse and a 10A fuse or is that over kill?

The original concept for all these cables was so that I could quickly switch to cigar sockets in the field, but it strikes me that I am over complicating things by doing that?

Thanks once again.

[symmetal]

Hi John,

The 40' cable  you're using at the moment, 1 mm2 made up of 32/0.2mm strands has a resistance of 19.1 ohms / kilometre which is 0.019R/m. Your 40' run is 12m which has a resistance of 0.23R per core. Total resistance is therefore 0.46R. Drawing 4A, a typical figure for what you've got connected to your distribution box, the voltage drop on the cable is 1.84V so you just have just 12.0V for your equipment. If you draw say 6A total when you're slewing with everything else still powered the voltage drop is 2.76V leaving you with 11.0V for your equipment. This is below the recommended voltage and could cause problems accounting for the weird noises from your mount.

The 2.0mm2 cable you mentioned has a resistance of 8.8R/km so at 6A current total drop is 1.27V. This leaves you with 12.53V across your equipment which is fine.

The cigar connectors will also drop some voltage as they have a small contact area on the tip and the inbuilt fuse and connectors will also add a bit more resistance. I would try and not use these connectors. The 5A you currently have in the cigar plug connected to the 30A terminals definitely needs increasing to its maximum of 10A to save it blowing like it currently is.

The option of having another connection to the cigar socket on the front of the Nevada powering some of your equipment (Dew heaters etc) is certainly an option which would reduce the voltage drop on your main cable but complicates running out your cables.

You said you're using cigar connectors to have the option of using it in the field, but you wouldn't be using your 40' cable in the field would you?

If you must use cigar connectors use the highest quality ones you can get. Instead of putting a cigar plug and socket connected right at the rear connectors on your Nevada, using the 25A cable you mentioned above, have a shorter cable to your distribution box ending in a cigar plug, fused at 10A, (say 10' long for use in the field) and a 30' long 25A cable connected to the rear terminals of the Nevada ending in a cigar socket. Put a 10A in-line fuse at the +ve wire at the Nevada rear as that's the rating of the cigar socket at the other end. You can get in-line fuse holders for blade fuses like the ones you're using. Using this method only one cable is needed to be run out from the Nevada at home, and in the field connect the 10' cable from your distribution box to your field power supply. Much shorter cable so voltage drop is not an issue. 

If you prefer, I can do a drawing of the above but see how you go.

Alan

[Jkulin]

That is brilliant Alan and makes perfect sense now.

No wonder skewing was a pain.

I've now ordered that cable and will reconfigure when it arrives.

i didn't plan on using a 40ft cable in the field, but reading my previous posts it must have sounded like that.

I suppose I really should have bought a rigrunner but for me my box is sealed and cost me a tenth of the rigrunner and is reasonably water tight. I never had a problem when I ran 240v out into the middle of my lawn, but some how I never felt safe.

I do have my original 8A Nevada which I could reserve purely for certain peripherals and then use the 30A for the heavy stuff?

Running two cables was never a problem as I could secure them together, along with my RJ45 cable.You post explains so much, thank-you all once again.

Clear Skies,

Regards, John

[symmetal]

Happy to help you out John. 

Hope the 25A cable will fit into your cigar connectors. If you wanted to run out two cables from your Nevada, you might as well use the front and rear connections on the 30A unit as it has more than enough capacity for everything. If you did use the 8A unit alongside the 30A one, connect the two -ve terminals together at the power supplies to have a common 'ground' reference.

Your distribution box is fine, and there's no need to have a more expensive one. 

Alan

[Jkulin]

Thanks Alan, I truly appreciate your knowledge and assistance.