(Re) wiring the batteries

[Grace and Favour]

Hi all,

 

Two quick questions:

 

1//

 

I'm just about to re-wire the batteries in the correct way (have been meaning to for a few weeks)

 

Cabling each battery (6 x 110 Ah) to a pair of busbars -

 

How should I calculate what rating of busbars to use please?

 

I assume it should be on the maximum demand my system could make (whether on shore-power or batteries) "plus a bit to be safe"

 

However - a more educated response than my carpenters logic would be much appreciated

 

 

2// - And where's the best place to buy busbars please? (they seem to be extraordinarily expensive at first sight - unless I'm looking in all the wrong places)

 

Many thanks

 

David

[Bimbly1]

2// - And where's the best place to buy busbars please? (they seem to be extraordinarily expensive at first sight - unless I'm looking in all the wrong places)

Can't help on the technical side but you may find some affordable ones here.

[RobinJ]

1//

Cabling each battery (6 x 110 Ah) to a pair of busbars -

 

How should I calculate what rating of busbars to use please?

 

I assume it should be on the maximum demand my system could make (whether on shore-power or batteries) "plus a bit to be safe"

Assuming this is on the domestic side, then add up all the demand and assume it happens at the same time!

Inverter 1KW - 100A, Water Pump - 20A etc.

A starter will pull 400 - 600A so going with the battery capacity is no guarantee!

Key point is not necessarily the capacity of the busbars, but the insulation?

[Grace and Favour]

Assuming this is on the domestic side, then add up all the demand and assume it happens at the same time!

Inverter 1KW - 100A, Water Pump - 20A etc.

A starter will pull 400 - 600A so going with the battery capacity is no guarantee!

Key point is not necessarily the capacity of the busbars, but the insulation?

 

Thank you Robin2,

 

You've confirmed my thoughts -

I take it that you are referring to the insulation of the busbars, ???

 

I thought that busbars are built and rated with the relevant insulation - - or am I making a dangerous assumption?

[RobinJ]

You've confirmed my thoughts -

I take it that you are referring to the insulation of the busbars, ???

I thought that busbars are built and rated with the relevant insulation - - or am I making a dangerous assumption?

Its not just the insulation on the busbars, but the whole set of connections, proximity of other conductive objects, bulkhead material etc., whether anything else can connect with them? Some have covers, some don't, then there are the terminations, wiring routes etc.!

I had a busbar (admittedly smaller with securing holes close to the strap) that when it was bolted on tended to short out (it was only designed to carry about 30A)!

Ever dropped a spanner onto the starter motor (easy when your fitting a new cable or adjusting the idle)?

[Gibbo]

It's not the current carrying capability you need to be concerned with. It's the voltage drop.

Edited March 31, 2011 by Gibbo

[WotEver]

It's not the current carrying capability you need to be concerned with. It's the voltage drop.

Translation: bigger is better

 

 

Tony

 

There are some reasonably priced ones here: http://www.leisureshopdirect.com/marine/marine_electronics/junction_boxes_and_busbars/Index_Marine_Busbars.aspx

 

Forget that - they're tiny

[Chalky]

It's not the current carrying capability you need to be concerned with. It's the voltage drop.

 

Also how hot you are prepared to let them run. The resistance that produces the voltage drop (R=V/I) also causes heat to be generated (W=I^2 * R). Bus bars will need to be supported and insulated from the structure and you'll need to connect each battery to them and from them to the alternator and the fuse/isolator/distribution board - more connections, more probability of a failure/fault. There may also be packaging issues as well as cost issues - big bits of copper / brass aren't cheap.

 

Most people wire them with large cables because its easier.

Edited March 31, 2011 by Chalky

[Grace and Favour]

This is the method I shall be using, with heavy cables. I had assumed (I know - to assume is dangerous!) that this was a straightforward exercise, and that it would benefit with the most efficient wiring of the batteries.

 

My original questions were:

How should I calculate the rating of the busbars

Can anyone recommend the best place to buy reasonably priced busbars please?

 

Many thanks

 

(The illustration and text below is an extract from smartgauge.co.uk)

Method 3

 

This looks more complicated.

 

It is actually quite simple to achieve but requires two extra interconnectng links and two terminal posts.

 

Note that it is important that all 4 links on each side are the same length otherwise one of the main benefits (that of equal resistance between each battery and the loads) is lost.

 

The difference in results between this and the 2nd example are much smaller than the differences between the 1st and 2nd (which are enormous) but with expensive batteries it might be worth the additional work. Most people (myself included) don't consider the expense and time to be worthwhile unless expensive batteries are being fitted or if the number of batteries exceeds 8.

 

 

 

 

 

 

 

With thanks to Smartgauge.co.uk

Edited March 31, 2011 by Grace & Favour

[bottle]

This is the decider:

 

The difference in results between this and the 2nd example are much smaller than the differences between the 1st and 2nd (which are enormous) but with expensive batteries it might be worth the additional work. Most people (myself included) don't consider the expense and time to be worthwhile unless expensive batteries are being fitted or if the number of batteries exceeds 8.

 

Yes, method three is the ideal but......................................

[stewart&jenny]

I have 5- 120aH batteries and they are connected up via :

 

http://www.es-store.co.uk/ac-changeover-systems-and-dc-link-box/dclinkpcbmeg5S.html

 

It may not be what you want but when it comes to making decent connections I rate it highly. Saves on the brain thinking and it does come with lots of nice protection (be aware, it quite a big box)....

[GUMPY]

My batteries are linked to two of these in an insulated box.

http://cgi.ebay.co.uk/400a-Neutral-Bar-Earth-Bar-6-way-/230400356291?pt=UK_BOI_Materials_Supplies_Electrical_ET&hash=item35a4ee6fc3

using equal lengths of 70sqmm HO7, then a single 95sqmm HO7 to the switch

but remember I am using 24v not 12v so one could say its overkill

[smileypete]

To get balanced connections to bus bars, you don't need equal length wires to each battery post, just the same total length to each battery:

 

 

That said for 6 batts maybe I'd connect them into 3 pairs then connect each pair to the bus bars.

 

cheers,

Pete.

[nb Innisfree]

We are 24v, the reason being when we first started planning our fitout I decided on a couple of busbar cables with separate fueboxes down each side of the cabin to supply a 12 microwave and all our other electrics (didn't know which side at that point) and estimated the cable thickness as somewhere in excess of 90sq mm, too cumbersome, so went 24v instead and could get away 40 sq mm. At a later stage when we had bought all the 24v stuff and fitted a 24v equipped engine I came to my senses and realised that as we needed an inverter for the w/m it would save lot of trouble to install a Victron Multiplus. As we had a load of 40mm cable we used that to run a couple of busbars for the macerator/pumps/fridge, no voltage drop at all.

 

There's never a straightforward solution.

Edited April 6, 2011 by nb Innisfree

[teapot]

To get balanced connections to bus bars, you don't need equal length wires to each battery post, just the same total length to each battery:

 

 

That said for 6 batts maybe I'd connect them into 3 pairs then connect each pair to the bus bars.

 

cheers,

Pete.

 

 

Is it possible to wire up six batteries, make them balanced, and yet not use bus bars?

I also wish to re-wire my battery bank but would like to re-use as much cabling as possible.

The diagram (method 4 here: http://www.smartgauge.co.uk/batt_con.html ) is ideal.

I would just need guidance for a similar method using 6 batteries.

Thanks all.

[WotEver]

Is it possible to wire up six batteries, make them balanced, and yet not use bus bars?

A large bolt with all the tags piled up nut-tag-nut-tag ?

 

Tony

[Bob18]

Yes, very possible.

Assuming your batteries are a nice compact area, say sitting on the uxtter plate:

The best way to connect batteries in parallel, for high current is the simplest - methods 1 and 2 on the linked page.

No messing, the simplest.

 

All the so called "balancing" arrangements do is use more cable, and do nothing to help balance the cells provided you use the right sized cable (or busbar). All the cables between the batteries need to be capable of carrying the output current of the bank, so if you have a 3kw inverter, that draws 300A, you need cables (or busbars) that will cope with 300A plus any inrush currents, so add 50%, so the cables need to carry about 450A. This applies regardless of what arrangement of cables you use. This works out at something like 150sqmm - which is in the camp of "sod-off big". If you have to double up the cable to get to this size, aim for a bigger area as there can be some extra losses caused by the extra connectors.

 

 

 

 

Busbars are better, but they only really work on batteries that have either stud or bolt-in connectors, both of which are better at delivering high current than the normal truncated, deformed cones. However the batteries these types of fitting are used on tend to be at the top of the price range.

[bottle]

Which makes the bolt a 'bus-bar'

 

Edit: this is in answer to post #16

 

as for post #17. :lol:

Edited September 13, 2011 by bottle

[Bob18]

No, its just a bolt with lots of connectors that are possibly connected properly.

 

You really shouldn't put more than about 3 terminals onto one bolt - I know we all do it, but it just isn't the best...

 

Busbars are quite easy to make - if anyone wants I can either do a simple how-to, or I'll do it by PM.

[bottle]

Sorry still laughing at post #17 :lol:

[smileypete]

Is it possible to wire up six batteries, make them balanced, and yet not use bus bars?

I also wish to re-wire my battery bank but would like to re-use as much cabling as possible.

The diagram (method 4 here: http://www.smartgauge.co.uk/batt_con.html ) is ideal.

I would just need guidance for a similar method using 6 batteries.

Thanks all.

Method 4 only really works for 4 batts, not 6.

 

You could try it like this, in 3 pairs of 2:

 

 

Just make sure the length of cable from the + and - of each pair of batts to the 2 common points adds up to the same in total as the other pairs.

 

You might be able to use one side of the batt isolator as the + common point, and the hull earth stud as the - common point.

 

cheers,

Pete.

[WotEver]

Which makes the bolt a 'bus-bar'

Well yeah, I knew that as I wrote it... I was at a bit of a loss really; "I have 12 connections to make, but I don't want to connect them together..."

 

 

Tony

 

You could try it like this, in 3 pairs of 2:

 

That works nicely

 

Tony

[teapot]

Method 4 only really works for 4 batts, not 6.

 

You could try it like this, in 3 pairs of 2:

 

 

Just make sure the length of cable from the + and - of each pair of batts to the 2 common points adds up to the same in total as the other pairs.

 

You might be able to use one side of the batt isolator as the + common point, and the hull earth stud as the - common point.

 

cheers,

Pete.

 

Thanks guys