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calculating needed gauge of long cable from power supply to charger?

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CharlesBlackstone

Jan 1, 1970
0
I hope to run a 40' pair of cables from my power supply (Mastech
3010E-3) to my charger (Thunder Power 1010C). Here's what I've been
thinking, I could use any thoughts you might have on the right way to
go about this. The Mastech push 60v/10a or 30v/20a and the TP 1010c
can charge at 10 amps (with 12 volts input I presume and will need 10
amps in).

I've been googling and found these cable gauge calculators, which tell
me I need 10 or 12 gauge to carry 20 amps for 40 feet, which doesn't
seem like much. But, most of them are calculating AC voltage I presume
since they specify 120, 220, etc volts.

http://www.gorhamschaffler.com/wire...calculator.html
http://www.freesunpower.com/wire_calc.php
http://www.elec-toolbox.com/calculators/voltdrop.htm

If I am pushing 60v and 10 amps, or 30v and 20 amps, is 10 gauge wire
safe? I was thinking about overkill for peace of mind and using 2
gauge; Autozone sells 2 gauge 20 foot jumper cables for $42. The TP
1010c can charge at 10 amps, and I presume at 12v. If I try charging
batteries, and the cabling stays cool, should I feel safe? I'm not
conversant with electrical stuff and nervous. The cable will run from
my office to the patio outside, through my house. If I can't feel safe
I'm going to move the Mastech next to the patio, but have reasons why
I don't want to do that.

Thanks.
Jim
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Phil Allison

Jan 1, 1970
0
"JeffM"
CharlesBlackstone said:
[...]I've been googling and found these cable gauge calculators,
which tell me I need 10 or 12 gauge to carry 20 amps for 40 feet,
[...]12 volts input[...]

My simple 4-banger calculator says 40 ft of 12AWG carrying 20A
will lose 1.5V before it gets where it's going.
As you only have 12V to start, that seems ridiculous.


** The OP clearly stated he has a 30 volt, 20 amp supply.

He is worrying about nothing.

Any 8 to 10 gauge (AWG) cable would do fine.




....... Phil
 
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CharlesBlackstone

Jan 1, 1970
0
First note:  I heartily recommend referencing Anixter's handbook of
electricity as a source for your questions on wire gauge and ampacity.

Your calculations should factor an 80' loop length (you will be pushing
and pulling current both into and out of the charger, so double the
linear distance to get loop length).  The sites you quote seem to be
taking that into account.

Voltage drop of #10 is roughly 1 ohm per 1000 feet (more conservative
references are as high as 1.25 ohms per 1000 at 75C), so expect 0.08 ohm
in your power transmission cable.  At 10A full load, you will have a
voltage drop of 0.8V, and a power loss of 8W.  If you want to be very
conservative figure 10W, and that 10W will be spread out along the length
of the cable.  It will remain cool to the touch.  Decide if that is
acceptable efficiency.  #10 should be your minimum choice.



This link doesn't work, I presume the elipses are fouling it up.


This link is recommending AWG #4 to carry 12V at 20A 40'.  That's a good
number based on the application.  This source wants to squeeze voltage
drop to a minimum.  The calculation is using 12V solar panels to chargea
battery.


This is the site that is giving you AWG #12 to push 20A along 40' one-way
(80' loop length as mentioned before).  I figure they're calculating for
a home circuit, where the wire is being sized for a 20A breaker.  That's
a different application as well, but ISTR that electricians will upgrade
house wiring to #10 for a 20A (as opposed to 15A) breaker.  I could be
wrong on that.


If you want to be conservative in both design and cost, use AWG #8.  #2
is going to be expensive and bulky, and #8 will have about half the power
loss of #10.  As the absolute most conservative design, use #6.  You can
find #8 in quality cable (THHN rating) for probably 40c per foot, so 100'
will cost you 40 bucks, a lot less than shelling out $84 for a pair of
crappy jumper cables that have to be spliced together.  See if you can
find #8 or #10 two-conductor sheathed THHN cable.  That might be your
best bet.


What, laying on the carpet in the living room?  Do you have a puppy?  
Small children?  Ah, I dare say, a wife who likes a nice tidy living
room?  12V isn't a lot, but at 10A it can produce a big flash and melt
and burn things (like nylon carpet, or a puppy's tongue) when shorted.  
Run it through the attic.  Er, by the way, does your Mastech supply have
output short circuit protection?

Thanks so much for the terrific answer. No, no puppy, children, wife.
Mastech does have short protection.

The thinig that is so attractive about the jumper cables is how
flexible they are. The multistrand wire at home depot has very thin
insulation and is not flexible at all. You have to bend it. Is that
two-conductor sheathed THHN cable you mention flexible like a jumper
cable?

20 ft 4 guage jumpers are $21 at Walmat. I can get smaller guages
cheaper but not in the long cables.

Jim
 

neon

Oct 21, 2006
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Joined
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Messages
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look at your PS does it have sensing terminals, if that is the case then it becomes a lot easyer to inplement with practcaly any gauges of wire since the load will be regulated to include I/R drop. otherwise use #14 anneled copper wire at 20 degrees ohms for 1000' is 2.525. but for a charger you realy should care about constant current as oppose to fixing the voltage to any value as long as it is greater.
 
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CharlesBlackstone

Jan 1, 1970
0
Ok, so you have no pressing need for output circuit protection.


Tray, duct and simple building wire aren't necessarily flexible.  Welding
cable is, but it's more expensive and tends to be thicker gauges.


Much of my answer is predicated on the belief that a wiring job should be
undertaken with a degree of professionalism and craftsmanship.  I
wouldn't take the jumper cable approach, especially if splicing is
required, but it's your project.  I'd find a more suitible route than
across the floor, unless it were a very temporary installation.  Take the
time to get a primer in cable crimping; as a minimum, you want good crimp
connections at both ends of the cable.  I'm hoping that you're not
considering using the spring-jaws as your permanent connection, but
again, it's your project.


Well, first, I rent, so can't make any permanent installations. Plus
the power supply may travel with me to the field and back and forth
between my motor test stand in one room and building bench in the
other.

I bought very heavy copper lugs for 8 guage wire, they screw down. I
bought a split bolt splicer. I haven't done anything yet, still
thinking things through. I'm noy sure how'd I'd insulate the splice.

But you raise an issue I have already been wondering about with your
question of using the spring-jaws.

When we charge batteries at the field we use a charger connected to
the car battery. That uses small spring jaws that come with most every
charger. In this and other cases where a spring jaw is used, the total
area of jaw touching battery must be very tiny, compared to the
thickness of the cable.

Is this a problem? It seems like the jaws would heat at those points,
and provide a tremendous resistance (though the distance is short,
true).
 
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terryc

Jan 1, 1970
0
20 ft 4 guage jumpers are $21 at Walmat. I can get smaller guages
cheaper but not in the long cables.

Stick/arc welding cables;long flexible & EEK $$$
 

neon

Oct 21, 2006
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Messages
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i SAY IT BEFORE AND I SAY IT AGAIN just because your charger can supply 20 or more amps it doesn't mean that you should try to push 20 amps into the battery. cars when running use ~7amps to run but the charge to the battery is not the 700 amps that was taken out to start the car. it takes time like 30 minutes to charge it TIME every battery like to be charged at a certain rate of current so the I is the criteria not the voltage.
 
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CharlesBlackstone

Jan 1, 1970
0
It's a trade-off.  Loss of conductance vs. ease of use.  In the case of
mobile application, the ease of connection to the battery is of primary
concern.


Thanks Charlie. It is possible to quantify how much conductance is in
effect when using the clamps? I am trying to decide if this is a safe
method, I need to deliver 10 amps/60 volts, would it drop that, or
just be a bad idea?

Thanks...
 

neon

Oct 21, 2006
1,325
Joined
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Messages
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do your math 10A 60V that is 600w you expect that continious into a battery get a life.
 
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