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Dinges
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| Posted: 06 February 2010 at 3:52am | IP Logged
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| If one adopts the practice of twisting the strands tight and soldering the exposed wire end before inserting it into the screw terminal than the resistance will not be such a large problem with time. Hence nor will the temp. problem. |
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Soldering/tinning the wires before inserting them into a choc block is actually a very bad practice. If you want to prevent the wires from being cut by the screw, put a 'cable sock' over it. (not sure what they're called in English; basically a piece of thin tube you slide over the exposed wires, to prevent damage from the screw end)
Note that the better choc blocks already have a piece of metal or tab in them that prevent the screw from directly touching the exposed wires anyway.
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| Undo the screw and remove the wire and see how many strands fall off, as well as look at how much of the copper conductor was actually in tight contact. |
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Fully agree with you there! I normally use these 'socks' too - it's a tiny detail, but it makes the difference between a professional job and something my grandmother would do.
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| I just didnt have the heart to tell Karl after all the work he put in setting everything up. |
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I have no problems with saying it to him. 
In fact, I'd want people to point out things they see in my work that could be improved upon - personally, I value criticism, and don't see it as a direct attack on my person. (not suggesting that KarlJ does, though!)
The difference between a job that is done 'good' or done 'professional, practically perfect' is usually only slightly and consists of details (like cable socks, cable lacing, heat shrink tube, neat routing, layout, etc.) And personally, I get a very good feeling when looking at a job done properly, either by myself or others.
Peter.
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Downwind
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| Posted: 06 February 2010 at 10:35am | IP Logged
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Peter once again you are very correct.
The point of tinning the wire ends is a case of the two evils (unless you have cable socks).
DC cable is often made up of fine stranded multi strand cable that gets destroyed with the screw terminals as we both agreed.
I still think tinning the ends is the lesser evil and would prefere it to not doing nothing and the screw cutting into the cable.
I seen this a lot with low voltage garden lighting.
400 watt 12 volt systems would burn out the terminal blocks.
It was always the connections with loose stranded ends.
The connections with tinned ends never gave a problem.
As you rightly pointed out cable socks and good quality terminals are a better option, but this is not always the case of what we have to work with.
At least with a tinned end you can torque that sucker down tight without destroying the conductors.
Pete.
Edited by Downwind on 06 February 2010 at 10:37am
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GWatPE
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| Posted: 06 February 2010 at 9:19pm | IP Logged
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If you try and buy cable socks, you will probably get a blank expression from the sales person.
I believe the items are normally called "boot lace ends"
Gordon.
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KarlJ
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| Posted: 06 February 2010 at 9:21pm | IP Logged
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OK so I've mounted the diode and the shunt on some cement sheet, do I need to protect them from people touching them?
Human body resistance varies from 1000 Ohms to 100,000 Ohms (wet fingers open wounds vs normal dry skin)
an it takes 10mA to cause pain
thus 60x60/ 1000 =3.6W /60= 0.06A
thus I guess theoretically could give you a lethal shock
at 60mA, if you touched it with wet fingers and were standing in a puddle of water....
Any ideas for a box?, obviously the heat sink still needs to dissipate heat thus fully enclosed defeats the purpose.
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Downwind
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| Posted: 06 February 2010 at 11:36pm | IP Logged
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No matter what you do to idiot proof something the idiot will still find a way around it.
If all you want is a protection barrier than place some blocks or posts each side and screw a sheet of clear plastic or mesh or what ever is handy over the top allowing good clearance and air flow around the sides.
A cover sheet and a couple of wing nuts to hold it in place should do.
Just a crash barrier if anything at all.
If some one is poking around under that then they should beware of the hazards.
Pete.
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Dinges
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| Posted: 07 February 2010 at 1:00am | IP Logged
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Thanks for that, Gordon. 'boot lace ends'... Just translated directly from Dutch. Tried googling the correct term for them... but that's the problem with google: if you don't know the correct search terms...
KarlJ, I understand anything below 42Vac is considered to be 'safe' from a shock-hazard point of view. About a month ago I did a little experiment, slowly increasing voltage till the point where I would feel it (dry skin, dry air, not standing in a wet puddle, but wearing leather shoes). It wasn't until 65Vdc that I could feel a tingling sensation, which wasn't even unpleasant.
That said, I normally make it a habit to not deliberately touch anything above 24V. It's always good form to shield electronics from direct contact. One day, it might be *you* who accidentally drops a spanner or screwdriver in it....
Not sure what your system voltage is; personally, at 24V battery voltage I wouldn't worry too much about electrical shocks (of course, when the battery gets disconnected from a running mill, voltages can end up much higher than that). At 48V, I'd take about the same precautions to be able to touch anything directly as I'd do at 230Vac. Better safe than sorry. Even though I've got my share of 230Vac shocks and lived to tell the tale.
Telecom systems use 48Vdc system voltage and from what I've seen, don't take any extra trouble isolating things from a shock-hazard point of view.
Just my thoughts on the matter.
BTW, nitpicking a bit, but human body resistance is always about 1 kohm; it's only skin resistance that can be much higher, a few 100 kohm is possible. Wet skin has much lower resistance though. Skin has also relatively low dielectric strength: at 230V, it simply breaks down and the skin resistance disappears... leaving you with just the body resistance, which is about 1kohm; 230V/1000ohm= .23A... which Hertz....
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| No matter what you do to idiot proof something the idiot will still find a way around it. |
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True... but I find the idiot for which I have to idiot-proof everything is usually myself....
Peter.
(PS: as usual, it depends.... 42Vac is normally considered to be safe; but I've heard that, when you're lying on your bare back in a steel boiler tank using a 42V tool (required in such cases; 230Vac is not allowed), you can still get a nasty shock from 42V.)
Edited by Dinges on 07 February 2010 at 1:01am
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KarlJ
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| Posted: 07 February 2010 at 12:37pm | IP Logged
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System voltage is upto 62V, I did notice when I was testing the dump loads at this voltage I was using my fingers to hold the wires on the terminals and wasn't getting so much as a tickle but you never know....
Anything that has fine wire on the ends going into screw terminals I have now soldered together, anything with a lug on it I have soldered anyway as the terminals I had werent big enough hence split them and soldered in.
Here's a pic of the isolation diode and shunt mounted on cement sheet,
I cant see any reason to mount any of the other bits on cement as they just shouldnt get that hot, I'll mount the SSR and heat sink on this piece of sheet too.
Power comes in from the mill on the left of the shunt, batt power goes to the diode and other power goes to the dump loads.
Small power wire going to the PL20 and connection is there for the huge cable going to the batts.
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Homegrown Power website : Forum Index
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Topic: Suggestions for Breakers
