Making Battery Cables for Inverters

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Making Battery Cables for Inverters

Postby bdosborn » Sun Oct 24, 2010 1:00 pm

For those of you who are adding inverters to your trailer, you're going to need some pretty big cables to go from the battery to the inverter. There are a couple of options for cables. You can use starter cables from the local auto parts store. This will work but there are a couple of problems with them. Most of the cables I've found are a #2, which limits your inverter size to around 1000W (depending on the cable length). Also, the insulation is cheap and the cable ends are crappy - flimsy and prone to corrosion. You're also stuck with whatever length they have. Another option is to have them made by an electrical shop using welding or locomotive cable. This will get you a better cable in just about any size and length you want but can be expensive.

Another option is to make your own. I used #1 marine cable from eBay with fusion cable lugs, which is good for245 amps outside the engine compartment. The fusion lugs don't require any special tools. You can buy a tool for crimp lugs but a good tool is expensive and I knew I probably wouldn't use it again for years. The cheap tools give you a sketchy connection so you get what you pay for. I got the fusion lugs and heat shrink tubing from here:

Lug Linky

There are two kinds of lugs that don't require a crimping tool, compression and solder. I've used both and I like the solder connections the best. Here's a video on how to solder the fusion lugs on, it really is as easy as it looks in the video.

Youtube Fusion Linky

Here's a picture of a cable I made to go between the two 6V batteries in the Boxcar. I color coded the ends to show the positive and negative sides of the battery (yeah, I'm kind of anal about wiring)

Image

Bruce

P.S. Here's a link torecommended wire size for inverters.
Last edited by bdosborn on Sat Nov 12, 2011 10:19 am, edited 1 time in total.
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Postby Shadow Catcher » Sun Oct 24, 2010 4:21 pm

On a smaller scale I was installing 10ga wire into 50A Anderson Powerpoles (I know over kill) solder ends. My wimpy Radio Shack soldering iron was not up to the task so I picked up a small/micro butane torch. Tinned the wire filled the connector with solder (holding with a pair of long nose pliers) and now have a good clean connection.
Welding cable might be a good source for making jumpers and finding connectors. I have 20+ft jumper cables made from 00 welding cable I salvaged from the scrapping of a 25MEV Betatron 35 years ago.
Fastenal has a good supply of lugs and cable at comparable prices.
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Postby bdosborn » Sun Apr 24, 2011 11:48 am

Still nervous about making your own inverter/battery cables? Here's a link to a company that charges $1 per end to build custom cables.

Genuine Dealz Custom Cables

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Re: Making Battery Cables for Inverters

Postby PcHistorian » Tue Mar 06, 2012 1:00 pm

Bruce, my hero. Battery and invert are right next to each other. Dc drops voltage per distance. That's why homes get it as AC. AC you can pump across the yard with 3 prong work cord. You try that with DC, well, not smart.

When I put in a separate battery for a car, many years ago, I ran one wire positive that I have made at a welding shop, they crimped on the wire connectors. Then I just ran the negative to frame ground. I could start the car from the second batter, as I had an old ford starter relay to throw the two batteries in parallel, during the start, then drop to 10 ga. for charge/run.
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Re: Making Battery Cables for Inverters

Postby IslandStorm62 » Mon Apr 14, 2014 5:33 pm

Is there a big difference with size and type of cable running from the battery to an inverter vice running a cable to the Progressive Dynamic Converter (PD4060)? I've be wrestling with the details for this electrical wiring and this is the first I've read about this issue?
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Re: Making Battery Cables for Inverters

Postby Dale M. » Wed Apr 16, 2014 8:47 am

IF you now the input needs (amperage) of the inverter...

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If in doubt always go one size larger in cable....

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Last edited by Dale M. on Wed Apr 16, 2014 7:34 pm, edited 1 time in total.
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Re: Making Battery Cables for Inverters

Postby bdosborn » Wed Apr 16, 2014 1:49 pm

Dale,

The chart you posted shows dangerously overloaded conditions for typical wire from the home center. Do you know what kind of wire it is meant to be applied to? For example, a #12 THHN stranded (building wire) WILL burn up if you use it on a 90 amp load as your chart recommends.

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Re: Making Battery Cables for Inverters

Postby Shadow Catcher » Wed Apr 16, 2014 6:46 pm

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Re: Making Battery Cables for Inverters

Postby George Taylor » Wed Apr 16, 2014 7:17 pm

I know the following due to the fact I am an electrician by trade. For a/c wiring 14awg is good for 20amps and 12awg is good for 25amps (even though you legally can only put 15 and 20 amps respectively), 10awg is for 30 amps, 8awg is 40, and 6 is for 55awg. This is for Ac not dc which the size will have to be increased. Here is a link to the numbers I have for ac.
https://www.facebook.com/ajax/mercury/a ... height=176

this is a chart for the dc size.
http://www.bluesea.com/resources/1437
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Re: Making Battery Cables for Inverters

Postby Dale M. » Wed Apr 16, 2014 7:20 pm

bdosborn wrote:Dale,

The chart you posted shows dangerously overloaded conditions for typical wire from the home center. Do you know what kind of wire it is meant to be applied to? For example, a #12 THHN stranded (building wire) WILL burn up if you use it on a 90 amp load as your chart recommends.

Bruce


Actually its for stranded wire on typical 12 volt DC.....And only intended to connect battery to inverter...

Help me out here.... Find chart you like better....

http://images.lmgtfy.com/?q=wire+gauge+chart

Maybe this one?

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Re: Making Battery Cables for Inverters

Postby bdosborn » Wed Apr 16, 2014 8:05 pm

Actually, the link posted above is a pretty good chart.
http://www.bluesea.com/resources/1437

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Use the 10% drop if you've never had a problem with (or heard of) voltage drop. Use 3% if you want to wring every last bit of power out of your system.

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Re: Making Battery Cables for Inverters

Postby MtnDon » Sat Apr 19, 2014 2:46 pm

My opinion stems from the realm of the DC power being "made" with PV panels and stored in lead-acid batteries. To me that means all loads are critical, not because of any performance issue of the involved electrical device but rather for the conservation of the stored electrical energy. I always use 3% as maximum drop when I calculate.

I just went through an exercise with the cargo trailer conversion. I had some lengths of 2 gauge copper welding cable laying around collecting dust and getting in the way. I thought I may as well give that a try for connecting the inverter to the two batteries. I cut a couple ends and added new lugs at those ends. I have a cable drimper I use in a hydraulic press. I did make the interconnection wire from one 6 volt golf cart battery to the other from a length of 2/0 welding cable I also had. There was approximately 5 feet of #2 gauge from the positive and negative terminals to the inverter DC inputs; slightly over 10.6 feet all told.

I placed a 980 watt AC load on the inverter. If we were running at 80% efficiency that might be about 1200 DC watts; 100 DC amps or so. The batteries were freshly charged and new. After a 30 second power up the #2 cables were getting warm. The voltage drop was sufficient to cause the inverter low voltage warning system to start beeping. That was a couple of weeks ago. Going by memory, as I took no notes, the voltage at the inverter inputs, under load, was down to about 11.4, more or less. According to many tables the #2 gauge wire should have been ample for the load. However the wires sure were warming up and the voltage was dropping. The individual wire to post connections were not hot; the wire itself was acting as a resistance heater. I am leery of many charts and tables for this reason.

But when I run the figures through my electrical designer reference program it advises me to use #1 AWG wire. (12 VDC, 100 amps, copper, 3% voltage drop, 11 feet total wire distance).

So I built new cables from the 2/0. The 2/0 wires remained cool, the voltage drop was considerably less... sorry I did not take notes on the actual readings and my memory is not all that great as to the actual value.

I guess I'm suggesting to be very conservative when using tables.
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Re: Making Battery Cables for Inverters

Postby citylights » Sat Apr 19, 2014 6:01 pm

Need special crimping tool? Nah, just a copper connector, sledge and hammer. Shove the wire all the way into the connector, tape the connection together. Place on the sledge head, tap the copper connector with the hammer until it crimps the wire good. Remove damaged tape, check connection, and re-tape.

Always, always use a fuse or breaker sized for the lesser of the wire or equipment. That way, the worse thing you can do is let the smoke out of the breaker or fuse... Not the wire or equipment.
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Re: Making Battery Cables for Inverters

Postby bdosborn » Sat Apr 19, 2014 6:07 pm

MtnDon,

You bring up a good point, especially for large (comparatively) loads and inverters. Using a cable with 10% voltage drop will result in 11.4V at the inverter, outside of acceptable voltage range for most inverters. That means you have to use the 3% values in the chart to size the wire properly. And you need to size for the inverters maximum surge value, not the continuous rating. However, looking beyond an inverter, 10% drop is acceptable for most other loads in a teardrop that aren't so sensitive to voltage drop - such as lights. But for simplicity sake, maybe using the 3% drop for all wire is the better approach, it's certainly the more conservative one. :thumbsup:

Bruce

P.S. I ran the number on your #2 cable and it should have only had a 3.6% drop according to this calculator:

http://www.nooutage.com/vdrop.htm

Not all wire is created equal, there's a big problem with counterfeit wire. Was it cheap wire?
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Re: Making Battery Cables for Inverters

Postby MtnDon » Sat Apr 19, 2014 6:50 pm

Bruce,

I thought the #2 would work as my calculator came up with 3.56% on an 11 foot distance. But the inverter sure did not like it. :(

The wire was salvaged from an old arc welder. I don't recall the brand and the cable markings only indicate voltage rating and wire gauge. Thinking real hard it might have been a Century... red like Lincoln and made in USA. Anyhow the 2/0 works like a champ! :) I'll hang onto the #2 for some lesser demand someday.
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