My 24V 200ah batteries came with what I can measure are 5mm core battery cables, I was not happy so used 8mm core battery cables. My question is why do they supply such thin core battery cables, surely it can be a fire hazard, I have attached a photo for size comparison

1 hour ago, Elro said:

surely it can be a fire hazard

what is the rating of your battery? 1C, 0.5C aka C/2, if it is rated at 100A (C/2), then the cable supplied would probably be ok, I think, also, is the suppled cable insulated with a silicon jacket? again, if so, its current carrying rating would be higher than a PVC jacketed cable.

Thank you for the info.

There are four factors which determine the cross sectional area of a cable

A] Cable Length

B] Cable Resistance

C] Operating Temperature

D] Current

Cable length and the cross sectional area of the cable has an influence on the resistance of the cable. The operating temperature also influences the resistance of the cable and also determines the type of insulation used on the cable. The current that the cable must be able to carry also influences the cable cross sectional area.

Silicone cable has a wider operating temperature so a thinner cable can be used for a short distance because the insulation of the cable would be able to handle the heat where PVC would not be able to handle the higher operating temperature and a thicker cable would be used so that the cable would not heat up and burn the insulation off.

To determine the cross sectional area of the cables in your photo one must either look at the cable insulation and see if it is not indicated on the insulation or measure one of the strands in the cable, calculate the cross sectional area of the strand measured and then count all the strands in the cable and multiply that by the cross sectional area of the one strand and that would be the total cross sectional area of the cable.

1 hour ago, GerhardK83 said:

There are four factors which determine the cross sectional area of a cable

A] Cable Length

B] Cable Resistance

C] Operating Temperature

D] Current

And perhaps an "E" for Acceptable Voltage drop. An acceptable voltage drop of (say) 1% on a 24V system will be much less than a 1% drop on a 48V system, and one might have to use a thicker cable on a lower voltage system with the same current (depending on cable length and resistance).

1 hour ago, GerhardK83 said:

Cable length and the cross sectional area of the cable has an influence on the resistance of the cable. The operating temperature also influences the resistance of the cable and also determines the type of insulation used on the cable. The current that the cable must be able to carry also influences the cable cross sectional area.

Silicone cable has a wider operating temperature so a thinner cable can be used for a short distance because the insulation of the cable would be able to handle the heat where PVC would not be able to handle the higher operating temperature and a thicker cable would be used so that the cable would not heat up and burn the insulation off.

To determine the cross sectional area of the cables in your photo one must either look at the cable insulation and see if it is not indicated on the insulation or measure one of the strands in the cable, calculate the cross sectional area of the strand measured and then count all the strands in the cable and multiply that by the cross sectional area of the one strand and that would be the total cross sectional area of the cable.

Solid advice Gerhard 👍

6 hours ago, Elro said:

My 24V 200ah batteries came with what I can measure are 5mm core battery cables, I was not happy so used 8mm core battery cables. My question is why do they supply such thin core battery cables, surely it can be a fire hazard, I have attached a photo for size comparison

5mm is diameter I assume? Thats about 19/20 mm2. It’s more than fine for your battery.

I have 35mm2 on mine but that’s because I have a 500ah bank but I only pull 125A max from it via DC breaker. I wanted a more future proof thing to not have to upgrade later again.

Edited Sunday at 06:202 days by Denns

5 hours ago, HennieL said:

And perhaps an "E" for Acceptable Voltage drop. An acceptable voltage drop of (say) 1% on a 24V system will be much less than a 1% drop on a 48V system, and one might have to use a thicker cable on a lower voltage system with the same current (depending on cable length and resistance).

@HennieL The voltage drop is a product of the current flowing through the cable and the resistance of the cable. See the image below, this is the formula to calculate the resistance of a cable.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/resis3.gif

5 hours ago, Denns said:

5mm is diameter I assume? Thats about 19/20 mm2. It’s more than fine for your battery.

I have 35mm2 on mine but that’s because I have a 500ah bank but I only pull 125A max from it via DC breaker. I wanted a more future proof thing to not have to upgrade later again.

@Denns The cross sectional area can be calculated by A = π r^2 or π D^2 / 4 or π * (D / 2)^2

Just a bit of junk info related to the picture. The supplied cable of 5 mm² seems to be coated aluminium which has a higher resistance and a lower current rating than copper. This is something one would normally get to save cost by China manufacturers.

This one can normally only see once you cut it. With car jumper leads one will also get a thick insulation of pvc to make you think it is a thick conductor.

6 hours ago, GerhardK83 said:

@Denns The cross sectional area can be calculated by A = π r^2 or π D^2 / 4 or π * (D / 2)^2

Yes, I got 19.6mm2. That’s why I said it looks to be a 19 or 20mm2 cable. Leaning more on 19.

1 hour ago, Scorp007 said:

Just a bit of junk info related to the picture. The supplied cable of 5 mm² seems to be coated aluminium which has a higher resistance and a lower current rating than copper. This is something one would normally get to save cost by China manufacturers.

This one can normally only see once you cut it. With car jumper leads one will also get a thick insulation of pvc to make you think it is a thick conductor.

I suspect it’s tinned copper. Not Aluminium. It looks like copper on the inside of each strand as in the picture but is a bit silver on the outside.

tinned copper has much much better properties than a purely copper only cable. The main benefit being less susceptible to corrosion.

11 hours ago, GerhardK83 said:

@HennieL The voltage drop is a product of the current flowing through the cable and the resistance of the cable. See the image below, this is the formula to calculate the resistance of a cable.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/resis3.gif

I am quite aware of the calcs... Guess you did not see the word "acceptable" before the voltage drop... Not serious, though - what is important is the fact that an acceptable drop of "x" % in a 12V or 24V system is a much smaller number than the same x% drop in a 48V system, and one should thus not solely rely on the four "factors" that you mentioned, but should also take into account the voltage of the system that the cables will be used in. As an example, if a voltage drop of (say) 1% is acceptable (and I know this is not, but makes for easy calculation...), then on a 48V system this would be 0.48V, but on a 12V system it would be only 0.12V, and if you had a drop of 0.48V on the 12V system the inverter or BMS would surely complain...

8 hours ago, Denns said:

I suspect it’s tinned copper. Not Aluminium. It looks like copper on the inside of each strand as in the picture but is a bit silver on the outside.

tinned copper has much much better properties than a purely copper only cable. The main benefit being less susceptible to corrosion.

The inside of the wire strands will not be greyish in color when you cut it if it was copper.. Those strands will have a copper color on the outside and greyish on the inside which means they are not tinned.

Hello everyone, some really sound feedback in this thread 👍

As a rule, I never spec the minimum cable size recommended by the inverter or battery manufacturer.

My goal is always maximum system efficiency and long term reliability. Buying thicker cable for the battery to inverter runs is a very small part of the total system cost, but it pays for itself many times over.

Main reasons I oversize

• Industry standard is ≤3% voltage drop on battery cables. Staying well below this often below 1% keeps losses to an absolute minimum.

• Over 5 to 10 years, the energy you save from reduced resistance losses more than pays for the extra cable cost often many times over.

• Dramatically lower heat buildup, which reduces cable temperature and brings fire or overheating risk down to almost zero.

Conductor choice is equally important. I always go with pure copper preferably tinned for battery applications.

It offers much lower resistance than aluminium and handles heat far better. Aluminium can be used in some long AC runs with proper upsizing, but for DC battery cables I strongly recommend copper.

The point is do it properly the first time. A few hundred rand extra on good quality copper cable now will give you better performance, lower running costs, and far greater peace of mind for the life of the system.

They say a picture is worth more than a 1000 words.

This picture looks very much like the 5mm cable in the 1st post.

When we strip the insulation we find no tinned copper but shining copper strands.

Should we use sandpaper on the strands this is what we get.

When a very good crimp with the correct cable sizes overheats suspect that it could be aluminium copper coated conducters.

10 hours ago, Denns said:

I suspect it’s tinned copper. Not Aluminium. It looks like copper on the inside of each strand as in the picture but is a bit silver on the outside.

Refer to my post with the 3 pictures showing no tinned strands.

I will cut the insulation and expose the strands and send the pictures for clarification, I used the cable on the left of the first photo

15 hours ago, Scorp007 said:

They say a picture is worth more than a 1000 words.

This picture looks very much like the 5mm cable in the 1st post.

When we strip the insulation we find no tinned copper but shining copper strands.

Should we use sandpaper on the strands this is what we get.

When a very good crimp with the correct cable sizes overheats suspect that it could be aluminium copper coated conducters.

Interesting @Scorp007. I’ve never seen a cable with copper coating and Al internals. Seems like a lot of work to sell a cable cheaper.

This article has some good information on tinned copper if interested.

https://www.crutchfield.com/S-JaPyDhdZ0JB/learn/what-is-tinned-copper-wire.html

44 minutes ago, Denns said:

Interesting @Scorp007. I’ve never seen a cable with copper coating and Al internals. Seems like a lot of work to sell a cable cheaper.

This article has some good information on tinned copper if interested.

https://www.crutchfield.com/S-JaPyDhdZ0JB/learn/what-is-tinned-copper-wire.html

Can I just add we find PCBs made to order where they at times make the tracks thinner and that affects us as we measure a volt drop to simulate the current drawn by devices. This is against our spec. Anything to lower their cost. Not fun to have to change SMD resistors due to this problem.

Aluminium is half the price of copper and we know how much cables are used world wide. $$$$ at stake.

Edited yesterday at 09:141 day by Scorp007

I cut some insulation off and the strands are coated, I scraped some and the strands are copper

2 hours ago, Elro said:

I cut some insulation off and the strands are coated, I scraped some and the strands are copper

And still you don't have an answer - likely because you have still not confirmed the current you will be running through the cable (as @Kalahari Meerkat asked), or the length of cable (between battery and busbar or inverter)... Anyway, here is some info that you can use to get an approximation...

From a Victron publication titled "Wiring Unlimited:

The app referred to above (Victron Toolkit) is quite handy...

And here is a lookup table From the same document:

Sorry late with this info The batteries discharge current is 100A The length of the cable to inverter is 970mm, so we can work off 1m each, I have 4 of these batteries in parallel connected to each other by 200mm cables

the length of the cable to inverter is 970mm, so this must be doubled for both negative and positive

So then, just to confirm: If the cable core (copper) diameter is ~8mm, that gives a cable cross sectional area of ~50mm2 according to the Victron table that I provided in my last post. If that is correct, than according to the Victron Toolkit app, at 24V and 2.0m total cable length, a 100A current will result in a voltage drop of ~0.7V, which should be acceptable - but I will stand back and let a qualified electrician confirm this.

That is how I see it as well, thanks HennieL