calculating needed gauge of long cable from power supply to

[CharlesBlackstone]

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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[JeffM]

CharlesBlackstone wrote:

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[...]

http://www.google.com/search?q=cache:aBNAbofjoOsJ:www.radiolocman.com/shem/shem-cache.html%3Fdi%3D18899+resistance.per.foot+12-00187&strip=1
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.

 

[CharlesBlackstone]

On Jun 16, 7:44 pm, Charlie Siegrist
<none.act...@this.time.check.back.later> wrote:

On Sat, 14 Jun 2008 18:55:16 -0700, CharlesBlackstone wrote:
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).

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.

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

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

http://www.freesunpower.com/wire_calc.php

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 charge a
battery.

http://www.elec-toolbox.com/calculators/voltdrop.htm

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 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.

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.

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.

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

 

[Charlie Siegrist]

On Wed, 25 Jun 2008 21:06:11 -0700, CharlesBlackstone wrote:

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.

Ok, so you have no pressing need for output circuit 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?

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

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

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.

 

[terryc]

On Wed, 25 Jun 2008 21:06:11 -0700, CharlesBlackstone wrote:

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 $$$

 

[CharlesBlackstone]

On Jun 26, 5:59 am, Charlie Siegrist
<none.act...@this.time.check.back.later> wrote:

On Wed, 25 Jun 2008 21:06:11 -0700, CharlesBlackstone wrote:
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.

Ok, so you have no pressing need for output circuit 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?

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

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

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).

 

[Charlie Siegrist]

On Thu, 26 Jun 2008 22:55:04 -0700, CharlesBlackstone wrote:

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.

I wouldn't use a split-bolt for a temporary or mobile cable. Typically a
split-bolt is used with bare ground cable, at least in my experience.
When insulation is required, I've seen it wrapped with electrical tape.
The splice is bulky, and the insulation wrap prone to fraying and peeling
if moved around a lot.

I'd use an inline crimp connector, which may come with its own heat-
shrink tube insulation. "Burndy" is a good source for info on these
crimps. You realize you can't use your 8ga. lugs on the 4ga. wire, I'm
sure

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).

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.

 

[CharlesBlackstone]

On Jun 28, 12:02 pm, Charlie Siegrist
<none.act...@this.time.check.back.later> wrote:

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).

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...