Afternoon All,

So, I have seen some discussions about this but would like to know if battery cable length makes a difference to the whole system over very short distances?

On the initial install, Battery 1 has a cable length to the switch of 55cm. On the second battery install a few months later, Battery 2 has a cable length of 1.1m.

The reason for the doubled length on Battery 2 is that the terminals are located on the right hand side of the unit and need to fold back towards the switch.

Is this difference in length a problem and should I consider getting the cables redone to match the same lengths exactly, i.e. 1.1m?

MdF

Yes, cable has resistance, longer cable has more resistance. For large currents it makes a difference.

Your one battery will always do the bulk of the work in an unbalanced system. How did you wire your second battery, post a picture

 

13 minutes ago, iiznh said:

How did you wire your second battery, post a picture.

Yes, I understand about resistance, but was more interested as to what impact this would have over shorter lengths of cable like in my system.

Below is the current wiring setup of the batteries.

MdF

Battery on the left will do most of the work and degrade more.

Correct way would be:

Connect Positive of left to positive of Right. Connect positive of left to Fuse positive.

Connect Negative of left to Negative of Right. Connect negative of right to Fuse negative.

 

Or make them exactly the same lenghts in the current config(assuming you have the exact same cable).

 

 

 

Edited March 2, 20224 yr by iiznh
youtube link

Thank you for your input. It is much appreciated.

Of the two options you stated, which would be the "more correct" or are they both doing the same thing in the end?

MdF

Edited March 2, 20224 yr by MdF

I have updated a link with an excellent video explaining the problem.

The "more correct" one would be the one using the least amount of cable. Cable = resistance and resistance = loss

It all depends if you can mount 2 wires securely to the battery terminals.

Thanks for the video link. Most interesting.

What suggest you guys for cable thickness for new cables? I currently have the 9mm cables on the system. Have spoken to an electrician and he suggests at least 16mm?

MdF

 

Edited March 2, 20224 yr by MdF

Max discharge of the 5KW inverter is 120A DC. (Just over 6KW)

Here is a sans table I found with Google

https://www.em.co.za/site/Catalogue PDFs/2020-Charts _ Tables.pdf

I would say 32mm (at the bare minimum 25mm) - just make sure that your fuse is weaker than the cable)

If you decide to go for 16mm since the loads is mostly small then size fuse accordingly

 

 

2 hours ago, iiznh said:

Max discharge of the 5KW inverter is 120A DC. (Just over 6KW)

Here is a sans table I found with Google

https://www.em.co.za/site/Catalogue PDFs/2020-Charts _ Tables.pdf

I would say 32mm (at the bare minimum 25mm) - just make sure that your fuse is weaker than the cable)

If you decide to go for 16mm since the loads is mostly small then size fuse accordingly

 

 

Perhaps a typing error. 32sq mm should be 35sq mm.

Not sure if the earlier post mentioning 9mm refers to outside diameter as the standard sizes are 4, 6, 10, 16, 25, 35, 50sq mm.

2 hours ago, Scorp007 said:

Not sure if the earlier post mentioning 9mm refers to outside diameter as the standard sizes are 4, 6, 10, 16, 25, 35, 50sq mm.

Apologies, yes I meant 10mm.

MdF

What I have done for my SunSynk 8.8K machine is connect my two Hubble batteries through a 120A fuse each using 35mm cable to a bus-bar. From the bus-bar to the inverter I have used 50mm cable. The max current the SunSynk 8.8K will draw from the batteries (irreverent of how many batteries you have) is 185A. My current bus-bars can accommodate 8 batteries. All 35mm cables from the batteries through the fuses to the bus-bar are of equal length. Each battery has it's own fuses for safety, and ease of disconnect if necessary.

Edited March 2, 20224 yr by TimCam

2 hours ago, Scorp007 said:

Perhaps a typing error. 32sq mm should be 35sq mm.

Yes, from looking up the table to typing something got lost in translation.

16mm = 87 Amps so just over 4KW... if you use 5KW from the battery then those will get warm (100A)

25mm = 115A so about 5.5KW (inline with what the inverter is rated for)

35mm = 140A so about 6.5KW (surge current that the inverter allows for a short time)

 

If 90% of the time you will use very little battery then 16mm might still work perfectly, just make sure your fuse protects the wire

 

Feedback from LiBSA confirmed the current wiring is correct BUT that cable length must be the same.

Booked the electrician for next week Thursday to redo the battery cabling.

MdF

Edited March 4, 20224 yr by MdF

3 hours ago, MdF said:

Feedback from LiBSA confirmed the current wiring is correct BUT that cable length must be the same.

Booked the electrician for next week Thursday to redo the battery cabling.

MdF

What a surprise.... To think that LBSA guide you that 10sq mm is all in order to use on a 5.1kwh battery at 48V. Load of 100A on this cable per battery can NEVER pass to get a COC.

4 minutes ago, Scorp007 said:

What a surprise.... To think that LBSA guide you that 10sq mm is all in order to use on a 5.1kwh battery at 48V. Load of 100A on this cable per battery can NEVER pass to get a COC.

Apologies, LiBSA only confirmed that the wiring layout must be as is and NOT what type of cable should be used (I did not ask them that question but will do so now).

My electrician has agreed that the cables do need to be upgraded to better quality and thickness etc.

MdF

Edited March 4, 20224 yr by MdF

6 minutes ago, MdF said:

Apologies, LiBSA only confirmed that the wiring layout must be as is and NOT what type of cable should be used (I did not ask them that question but will do so now).

My electrician has agreed that the cables do need to be upgraded to better quality and thickness etc.

MdF

OK good.  25 will do but 35 is put in and forget and have peace of mind.

10mm = 65A... per battery which is fine only if each battery has its own breaker rated for the 10mm

 

If you combine them like you did then the breaker must still be rated to the 10mm wire, nothing more.

One battery could go offline to to low cell cutoff causing the remaining batttery to deliver all the current

For the price you pay for a couple of meter 50mm² welding cable, why do you want to skimp on decent cable? Any losses will be there for ever. I bought 50mm² red cable and just put black shrink sleeving over the - cable.

LiBSA have confirmed that 25mm2 will be the bare minimum but anything above will be good too.

MdF

1 hour ago, MdF said:

LiBSA have confirmed that 25mm2 will be the bare minimum but anything above will be good too.

True, but under full load (100A) it will warm up and attenuate the flow of current. 35mm is not that much more per meter, and if the funds are available rather go for 35mm.👍

On 2022/03/02 at 9:48 AM, iiznh said:

Battery on the left will do most of the work and degrade more.

Correct way would be:

Connect Positive of left to positive of Right. Connect positive of left to Fuse positive.

Connect Negative of left to Negative of Right. Connect negative of right to Fuse negative.

 

Or make them exactly the same lenghts in the current config(assuming you have the exact same cable).

 

 

 

Looks like there is no BMS coms between the betteries, with BMS and one battery as a master, there should be control on charging and discharging of all batteries in a bank. With BMS,I don't see how one battery will be 100% while others are lagging behind. I stand to be corrected  

Hi,

Yes there is comms. If you look carefully, the yellow network cable goes from the CAN port on battery 1 to the inverter.

The grey cable goes from parallel port on battery 1 to parallel port on battery 2.

So there is control from the inverter and between batteries.

MdF

18 minutes ago, hoohloc said:

Looks like there is no BMS coms between the betteries, with BMS and one battery as a master, there should be control on charging and discharging of all batteries in a bank. With BMS,I don't see how one battery will be 100% while others are lagging behind. I stand to be corrected 

Edited March 4, 20224 yr by MdF

2 minutes ago, MdF said:

17 minutes ago, hoohloc said:

Looks like there is no BMS coms between the betteries, with BMS and one battery as a master, there should be control on charging and discharging of all batteries in a bank. With BMS,I don't see how one battery will be 100% while others are lagging behind. I stand to be corrected 

was a comment on the video shared by @iiznh

Morning All,

So, went with the 35mm2 cable and the matching lengths have just been installed.

Now waiting for the batteries to get to 100% SoC for balancing and then I should see better matching data from the two batteries.

MdF

3 hours ago, MdF said:

Morning All,

So, went with the 35mm2 cable and the matching lengths have just been installed.

Now waiting for the batteries to get to 100% SoC for balancing and then I should see better matching data from the two batteries.

MdF

A picture of the new cables.

MdF