Crimping Battery Cables, your opinion?

[roks]

Hi All,

I am setting up a inverter and battery bank, I made some cables (70mm2) with a hydraulic crimper from eBay. Results are OK'ish but wanted your opinion whether to crimp it twice (overlaps a bit) or just once in the middle of the lugs.

I've attached picture of both two (on the left) and one crimp (on the right) and do they look OK.

Thanks in advance.

PS: I will be filing down the sharp edges and heat shrinking it later.

 

[ericmark]

With that type of crimper I would just do it once. I had a problem with that type as the auto cable was really around 60mm and the auto crimps were designed to be soldered, so I used mains type crimps, but the dies did not grip the cable that well, so I used the cheap crimp pliers with the adjustment screw 10 - 120mm with those I did crimp twice. If you have got 70mm cable and 70mm crimps then no need for double crimp.

With inverters I used 2 x 35mm cable as the 70mm put too much strain on the lugs. Getting 4 x 35mm cables to look neat between batteries and inverter on the narrow boat is much easier than 2 x 70mm cables which simply don't like to bend, I used welding cable with some and auto electric with others, the welding cable was a lot more flexible.

 

[roks]

Hi ericmark,

Thanks for the reply.

My cable and lugs are 70mm2 and the crimper has the right size die 70mm2 as well. I wasn't sure if it was ok to do overlapping crimps on the lugs. I had some cheaper bell mouth type lugs and I could easily fit 2 crimps but these are straight end, seem to be little shorter hence the overlap.

I did buy some ready made 95mm2 but they were not flexible so I went for 70mm2 much more manageable. then realised there is flexible version of 95mm2 with fine strands as well but due to weight and other issues, stuck with the 70mm2. Manual calls for 4/0 but I don't see myself maxing out 3kw.

 

[ericmark]

The one I fitted was 3kVA with 6kVA peak, but from 3 x 160 Ah lead acid batteries there is clearly a limit as to how long one can draw 3kVA. It was a failure, hind sight needed 24 volt not 12 volt and the inverter was poorly made. The inverter had a row of FETs each one with a spade type 16A fuse which it seemed was also used to ensure the load was spread through out the array. However it did not share load and there was no indication when a fuse failed, so slowly more and more load went on to the remaining FET's until blue smoke was released.

Boat was sold and new owner swapped from 12 to 24 volt, quite expensive swap, but worth it in the end, new inverter was better quality and 24 volt and was able to deliver the full 3 kVA. The new alternator is insulated return and batteries are centre tapped so lights are every other pos and neg earth. Engine had two alternators so engine start still 12 volt. Now 7 x 160 Ah batteries not 4 x 160 Ah, and the inverter also charges the batteries when on shore supply. Original charger only supplies engine start battery. Also a three stage regulator fitted in the 24 volt alternator to speed up re-charge.

The original theory was sound, 4 amp shore supply to battery charger to 3 batteries used for domestic then an inverter from batteries so washing machine could be used, the heater on washing machine was on for such a short time and the inverter drive motor did not mind the simulated sine wave supply, we used a welding cable plug and socket so battery could be isolated if required. However in practice the cheap Chinese inverter was rubbish and so whole idea failed. But also baby resulted in a re-think about living in a narrow boat, so boat was sold before the problem was rectified.

 

[roks]

Mines a 24v Outback inverter, 5.7kw peak for 30 sec, 4kw for 5min then 3kw. I will start with 2x 200Ah to start with and then add more if the load get bigger or requires longer runtime.

 

[roks]

Another this that bugging me is that my main cables and battery interconntion cables are not exactly equal lengths, they are about 15-20mm difference in length.

How much of problem is that going to cause if any? As hear talks about how important it is to keep cales equal length.

 

[ericmark]

No problem it's DC

 

[roks]

Thanks ericmark,

Will it not have different resistance if I have cables of different length?

Or do I not have to worry about that.

 

[chivers67]

I'd get a small amount of Heat shrink on the ends, i always use it on lug crimps - looks much better too

 

[JohnW2]

I'd get a small amount of Heat shrink on the ends, i always use it on lug crimps - looks much better too

PS: I will be filing down the sharp edges and heat shrinking it later.

Kind Regards, John

 

[chivers67]

sorry didn't see that underneath the pic

 

[ericmark]

Will it not have different resistance if I have cables of different length?

Yes but that is not why AC cables should follow the same route and be near same length, even with AC the problems only really start when you hit radio freq.

There is a problem with split charging if the cables are not same resistance, but only with multi split charging diodes.

I have had it with a boat where two Lucas split charging diodes were used in parallel, cables were simply run from one diode to next one, what was needed was independent cables from alternator to diodes and diodes to battery then they load shared. However that's charging the batteries not linking them to an inverter.

From what you have said I can see no problems with one cable being 0.0011Ω and other 0.0014Ω it will not affect anything.

 

[Jackrae]

If you cables are REALLY flexible (such as welding cable) and run together, be aware that they will try and move away from each other when carrying high currents - so firm fixing or tie-wraps may be necessary

 

[roks]

Thank you guys for your help, much appreciated, I'll be using cable ties to keep them together.