What cables to use on my inverter?

[howardb]

I just received my new 3000w/6000w 12v inverter and want to hook up the two 12v 102Ah deep-cycle batteries I have - I know the batteries must be connected in parallel -- "+" to "+" and "-" to "-", but need some advice on what the best cables are to use - I had a look in Builder's Express, and they have welding cables (green ones) that seem to be rather thick - they also have some car jumper cables that are rated to 180 amps, 200 amps and 275 amps - what should I be using to avoid cable overheating?

The shorter the cables the better, so I will try and keep them to a maximum length of approx. 40-60cm for both.

Should I be using cables with pre-crimped terminal lugs, or could I just bolt the wire to the battery terminal block?

I also need to know if the cables should run from the inverter in a 2 x 2 configuration - i.e. 2 from the "+" to each battery and the same for the "-", or can they be connected by bridging the terminals?

Any assistance or advice appreciated...

...just about to be load-shed, so will check back on the thread later... ...irony...

 

[quovadis]

Any decent sized cable will be sufficient - by decent I mean jumpercord approximate width and quality. The batteries need to be put in parallel. I'd suggest direct to inverter instead of to each other and then to the inverter just in case although it shouldn't make a difference but don't put them in series as this will create 24v which would be bad

 

[.Froot.]

Connecting 2x12V batteries in series with a 12V inverter is a big no-no. So you should stick to parallel.

The bigger the better, when it comes to cabling. A 3000W inverter pumps out a whopping 275Amps under full load so you'd better come armed to handle that (I'm not kidding, it really does pump out that much).

The cables should only be as long as absolutely necessary. The longer the cables, the bigger your resister and the hotter they become. (If you double the coils on your stove, they theoretically become twice as hot.)

Thus my professional recommendation would be that you go ahead and buy the 275Amp cables. You should connect the cabling to the batteries in such a fashion that you use as much as possible of the terminals on the batteries (the connected surface area on the battery determines the amps it can handle, if that is smaller than the cabling). Therefore the bolt-style that is used on a car (get the best you can afford) is your best bet.

Lastly, bridging your terminals is the best configuration as you should remember the following simple rule: the less cable you have the better.

This is pretty much all there is to it. Really lastly, never completely discharge your batteries. That's almost the same as leaving your headlamps on for a week- you destroy the battery, not just run it empty. (In a deep-cycle battery you still damage the battery but not as bad as a car battery).

 

[howardb]

Many thanks for the replies and advice chaps - I'll go with the largest jumper cable load they have and connect as per suggested to the battery terminal blocks.

Will bridging the batteries cause any problems with the charging cycle of each battery? I'm just a bit worried that the battery that's located the closest to the inverter on the cable will receive more of an over-charge than the one located a bit further away - need I worry about this at all?

I should be looking at a connection like this then:

 

[.Froot.]

Many thanks for the replies and advice chaps - I'll go with the largest jumper cable load they have and connect as per suggested to the battery terminal blocks.

Will bridging the batteries cause any problems with the charging cycle of each battery? I'm just a bit worried that the battery that's located the closest to the inverter on the cable will receive more of an over-charge that the one located a bit further away - need I worry about this at all?

I should be looking at a connection like this then:

That is quite correct. I don't see any problem with the charging, however, but if it does worry you, you can always connect the batteries direct to the inverter (no performance differences, just a little extra heat, but shouldn't be worried about).

Some chargers have built in devices that switch off when the battery is full, but I am unsure of how this will work on more than one battery. In this case it might be better to charge each battery individually. If you buy the charger at a store maybe ask them??

 

[Gnome]

At that load nothing less than 0AWG.

Although the rating on the cable itself is important don't trust them for face value, some of them are inflated which is why I say 0AWG.

 

[Wino]

Interesting thread!

Where can I get hold of an inverter, and are there several different types etc?
I only want to be able to run my PC, screen and ADSL modem.

Is this a better option than a UPS?

 

[.Froot.]

take a look at www.bushpower.co.za
Their prices are pretty decent. According to most people I've talked to, our power is so bad that it equivalent to a modified sinewave, so if you can't afford a pure sinewave inverter (those are pretty expensive), buy a modified sinewave inverter. Assuming you have a 500W PSU, 150W screen and 50W router, you need a 1KVA/1000W inverter. Just get mega-thick cables for the battery as the current going through a 1kW inverter goes up to ~55A.

 

[howardb]

Just a quick update -- I managed to get my hands on some real heavy duty jumper cables that are rated to 400 amps, are approx. 1cm diameter, and have the lugs crimped at each end - will be using these for the connection now and they should be sufficient.

I just need a confirmation as to whether I can maybe have the battery ends of the cables running straight through, without cutting them and making straps between each battery - a bit difficult to explain, but is as follows:

- cut the cable to the correct length as required, with a lug on one end and bare wire on the other.
- connect the lug end to the inverter terminal.
- place the battery terminal fittings on each battery terminal, with the clamps in-line with each other, from "+" to "+" and "-" to "-"
- cut the plastic covering off the bare end about 1cm-1.5cm at the end.
- cut a section of the plastic covering off where the second battery terminals intersect - so that the wire is a single straight piece that can be clamped in-line with each battery.

Does this make sense, and will it work?

Diagram I put together to explain the connection better as follows:

 

[.Froot.]

It sounds okay. Just make sure that you have "maximum covered area" when it comes to connecting the battery terminals to the cable. You don't need a source of excess heat there. But from your diagram it looks quite sufficient.

The 400A cables are the best thing I've heard recently. Compared to "recommended specs", you shouldn't have any excess heat at all.

 

[howardb]

Thanks for all your advice and assistance froot - will post here when I have it all connected up and running... if the 400A cables overheat then I'll be seriously surprised.

...all I need to find now is a decent 2 or 4-battery steel battery housing with castors...