Battery charging/connecting cables....what gauge?

[jenevers]

The cables on my batteries are like welding cables!

I'm re-configuring to a different layout with new batteries. Does the new cabling need to be so big?

[Taslim]

The cables on my batteries are like welding cables!

I'm re-configuring to a different layout with new batteries. Does the new cabling need to be so big?

Sounds to me as if they need beefing up!

 

For a serious reply we need more onfo. How many Batts and what capacity (Amp hours). Output of your alternator. Demand from Batts. Present and planed configuration will do for starters.

 

Personaly I'd be delighted to find my system 'over wired'.

 

Edit for spilleng mysteak.

Edited February 8, 2016 by Taslim

[Chewbacka]

The cables on my batteries are like welding cables!

I'm re-configuring to a different layout with new batteries. Does the new cabling need to be so big?

The boat safety scheme check specifies cables "The battery cables prescribed in the check must be approximately 25mm2"

You also need to consider the max current to avoid volt drop. So just a few lights and 25mm2 should be fine, try running a 3kw inverter, fridge and some other stuff and 25mm2 is too small, especially if the inverter is 2 or 3 meters away from the batteries.

So short answer to your question is yes.

[jenevers]

 

4 X 180Ah batteries, 160 A alternator, 2 Kw inverter

The cabling to the charger and inverter will remain the same, it's just the cabling between the batteries that will be new.

Edited February 9, 2016 by jenevers

[WotEver]

Yes they need to be really good and fat

[Chewbacka]

4 X 180Ah batteries, 160 A alternator, 2 Kw inverter

The cabling to the charger and inverter will remain the same, it's just the cabling between the batteries that will be new.

The cable between the batteries will still be carrying the inverter current and thin cable here will also add resistance so the nearest battery to the inverter will end up doing more work and dying sooner.

The battery interconnecting cables should not be thinner than the inverter supply cable.

 

I know you did not ask, but for a 2kW inverter where each cable is less than 1m in length I would use at least 35mm2 and if further then thicker.

 

Note - This would give you a voltage drop at full load of 1.5% for the cables and a bit more for the connections/switches and this is just the inverter. If the fridge is running as well and a water pump etc then your peak current could be up to 200Amps. For that I would use at least 50mm2 between batteries, with at least 35mm2 to the inverter (assuming within a meter) and same for the alternator.

Edited February 9, 2016 by Chewbacka

[WotEver]

Note that the size of the battery interconnect cables and the quality of their connections is critical to getting the most out of the batteries. No point losing power before it's even left the bank.

The cable between the batteries will still be carrying the inverter current and thin cable here will also add resistance so the nearest battery to the inverter will end up doing more work and dying sooner.

Not if the bank is correctly cabled it won't.

 

By which I mean taking the feed from opposite corners for a 2 battery bank etc.

http://www.smartgauge.co.uk/batt_con.html

[Sea Dog]

Mine are 75mm - I count myself lucky.

[nicknorman]

For battery interconnect cables the distances are presumably short so one way of looking at it is that very thick cable is not needed. However the other way of looking at it is that a short length of very thick cable is cheap. Personally I'd go for 75mm^2 cable. If you get the extra flexible welding cable, it is less of a nuisance than the more rigid stuff (which has fewer, thicker strands).

[bottle]

Being as size matters, behave boys, mine are 50mm² on a 24v system.

[Paul C]

When I did mine, the critical part is getting the thickness of the inverter supply (and return) cables right. With a large inverter, located in the cabin area; but the batteries in the engine bay (on a semi trad stern) and with a couple of bulkheads in the way too (one of them thick metal) the cable run had to be around 3m. So that's quite a long run for inverter supply cables, so all the factors come into play:

 

- excessive voltage drop

- routing thick cables around items and through bulkheads

- cost

 

etc

 

In the end, I went for 70mm2 and I bought 10m (5m each of red and black), which cost a fair amount. And the hydraulic crimper and a bunch of terminals and heatshrink etc. With the unused cable I was able to completely redo the battery cables too, so these were also 70mm2. Yes, the interconnects will only carry a proportion of the highest demanded current so you could size them lower if you really wanted. BSS demands a minimum of 25mm2.

 

Also bear in mind when you get to making very short (thick) cables, that the relative angle of both terminals becomes significant, you can't just "twist" the cable round to fit, and the length also needs to be accurate.

[WotEver]

Mine are 75mm - I count myself lucky.

Yup, me too. I still have a few metres of 75mm kicking around somewhere.

 

Tony

[xub1]

This has got me thinking, I have a 210ah battery and 40amp charger, and 1k Honda generator.

 

I know that the generator and battery charger can deliver it, but that the battery cannot accept all of it. The battery is kept charged up, so at best I can get in about 8amps and then down to about 4 or two amps, at which point it isn't worth running the generator.

 

It is a good set up, I think, for my needs. The charger wires are heavy duty. BUT, I am now thinking what about when it comes to the connection between the clips and the battery terminals, for they only touch a a few tiny points, and maybe that is a weak link in it all, a 'resistance blockage', as maybe it is like having some thin cable in the circuit which is limiting the amp flow. and so if I make a better connection then maybe I could get more amps in than I am now able to. Anyone any thoughts?

 

Incidentally, I went to Birkenhead last Friday to have a look at the u-boat they have on display (cut it into sections so you can see inside). I was looking at where the battery bank is and reading the blurb. It was like what we talk about here, but every number had many zeros after it. Serious stuff. Makes me laugh when i think that I'm just running a small tv and whale water pump, and then all the stuff that they were running, inc propellers and plane fins, ballast pumps. Amazing.

[Chewbacka]

.....................................Also bear in mind when you get to making very short (thick) cables, that the relative angle of both terminals becomes significant, you can't just "twist" the cable round to fit, and the length also needs to be accurate.

 

On a fat short cable the difference in path length between the inside and outside of a tight bend is huge, so I crimp one end, cut to slightly too long bend and hold into shape then cut to length and crimp.

[WotEver]

The charger wires are heavy duty. BUT, I am now thinking what about when it comes to the connection between the clips and the battery terminals, for they only touch a a few tiny points, and maybe that is a weak link in it all, a 'resistance blockage', as maybe it is like having some thin cable in the circuit which is limiting the amp flow. and so if I make a better connection then maybe I could get more amps in than I am now able to. Anyone any thoughts?

 

If you wiggle the clamps, does the charging current raise? If not, then your connection is good enough

[rupertbear]

By which I mean taking the feed from opposite corners for a 2 battery bank etc.

http://www.smartgauge.co.uk/batt_con.html

 

What's the best arrangement for five batteries? I have been trying to work it out but my brain hurts.

 

I suspect that there isn't a solution which equalises all the paths given an odd number of batteries, if so what's the best compromise?

 

Or should I stick with the simple 'opposite diagonal' connections?

[WotEver]

 

What's the best arrangement for five batteries?

Method three

[rupertbear]

Method three

 

Not practical, I'm afraid.

 

I think I'll go for the simple corner to corner unless anyone can come up with a better idea?

[WotEver]

 

Not practical, I'm afraid.

 

I think I'll go for the simple corner to corner unless anyone can come up with a better idea?

That'll work fine if you ensure that you use very fat interconnect cables - at least 70mm - and good quality crimps, secured tightly to the batts.

 

Tony

[Loafer]

Don't go mad with the tightening to the battery terminals though, they're only lead or copper and it is easy to strip the threads.

[Arthur Brown]

Cables from charger to battery need to carry the charge current safely without much volts drop They need a fuse at the battery end to protect the cable against the battery feeding a short circuit and killing the cable.

 

Cables from the battery to the consuming appliances need to be scaled to the usual max load and permissible volts drop.

[Col_T]

I also have 5 batteries in the domestic bank, and having been trying to get my head round this with what sounds like the same result as you! The obvious solution is method 2 from the Smartgauge page linked to, though that is not optimum. I have dreamed up a much more whacky solution, though I have doubts that it will work. I'll describe here so that those who understand these things can tell me why it's a rubbish idea.

 

Start with method 4 from the Smartgauge web-site which gives you two pairs of connected batteries, which we'll call A and B. Place the fifth battery between A and B and connect A and B together as per the diagram. Then connect the +ve from the fifth battery to the +ve of battery A, and the -ve from the fifth battery to the -ve of battery B, and then connect the cables to the load / battery charger as per the diagram. See, told you it's whacky!

 

All comments on the above gratefully received, though I'd appreciate explanations of why it won't work so that I may try and learn a little more!

[WotEver]

Method 3 would be the best but requires extra busbars and is messy. Method 2 isn't very bad.

 

The above 'modified 4' won't work because the whole point of method 4 is to give every battery exactly the same number of connections with the same total length of cable.

 

Tony

[rupertbear]

I have given more thought to this and made some pretty pictures. I have found a way (thanks to input from Col_T) which I believe gives an 'equal' interconnect length to each battery. However. because of its complexity and the fact that four connections would be required at one battery post, I shall not be using this method.

 

Gibbo says: Even with 8 batteries it is possible to get reasonable balancing by placing the main "take off" feeds from somewhere down the chain instead of from the end batteries.

 

With this in mind and other remarks he makes about diminishing returns I have decided to go for a 'modified diagonal'. The connections to the bank will be at Batteries B and D, where the bank is A to E connected in a parallel chain. If my calculations are correct, this gives a ratio of 9 : 7 where A and E are 9 and B,C,D are 7. Ideally the ratio would be 1 : 1. I can live with this and will move the batteries round occasionally.

 

 

 

[nicknorman]

Yes I think you are absolutely right to do it that way. Provided you have adequate cabling and keep the connections in good condition (ie low resistance) it doesn't really matter too much what the topography is.