Morning All, I was supplied 25mm double insulated cable to connect my 4 x 200ah batteries to my Growatt SPF5000ES inverter.

Is this 25mm (87Amp rating) cables any good or do I need to spend a extra R1000 to get 35mm cable(105amp rating)?

10 hours ago, Koppies said:

Morning All, I was supplied 25mm double insulated cable to connect my 4 x 200ah batteries to my Growatt SPF5000ES inverter.

Is this 25mm (87Amp rating) cables any good or do I need to spend a extra R1000 to get 35mm cable(105amp rating)?

Best get the recommended 35mm sqr cable if you can, your inverter's max Charge current is 100A

 

5 minutes ago, hoohloc said:

Best get the recommended 35mm sqr cable if you can, your inverter's max Charge current is 100A

Can it be 25mm between batteries with 35mm from Inverter to battery? 

14 minutes ago, swazz99jhb said:

 

Can it be 25mm between batteries with 35mm from Inverter to battery? 

My advice is based purely on the inverter spec sheet. The max charge current for that inverter is 100A. I don't have information on the 4 batteries that are being used but if all four are connected in Parallel, that means 25A max charge current per battery. Then yes, you can use the 25mm spr cable between them. 

If you have the 25sq cable already just double up each connection which gives you 50sq which is lower resistance than than 35sq and much easier to work with. Saves you having to buy new 35sq cable...

Irrespective of the capacity of the inverter  to supply 100A to the batteries, what is the spec for the battery BMS, will it allow 100A ? 

The pylontechs only allow C/2 +- 5A, max. I have 4XUS3000's, 147h, max charge rate I've ever seen in 18 months is 80A = 3840W and 95A draw for a short period (dont ask, but it has to do with a hairdryer and microwave)..

Also what is the max draw your inverter can take from the batteries?

Take that into account  then decide how what cable you need...

Edited April 21, 20215 yr by FixAMess

1.       Obtain battery specification first.  

        Typical spec for a 12V 200Ah lead acid gel

-         x4 12V 200Ah Lead Acid Gel Battery

-         Connection is in series thus Battery Bank = 48V 200Ah 

-         Max Battery Charge Current = 46A

-         Max Battery Constant Discharge Current = 45A

-         Battery 5 Sec Discharge Current =  1850A

-         Battery Short circuit current = 3422.5A 

2.       Obtain DC cable specifications (for 25 and 35 mm2)

-         Max continuous current rating of a 25mm2 cable = 104A

-         For a 35mm2 cables - Volt drop @45A =  351 mV

-         For 25mm2 cables - Volt drop @45A = 459 mV

-         For a 35mm2 cable the fault rating for 1 sec = 4025A

-         For a 25mm2 cable the fault rating for 1 sec = 2875A 

3.       Recommendation:      25mm2 cables will be suitable

-         Ensure Correct SCPD i.e. Fuse are selected

-         Volt drop is negligent <1%

-         Refer to battery manufacturers spec first before sizing cables

-         The 25mm2 cable is rated for 104A continuous current

Note: 

-         Only  fuses to be installed (due to its fault current limiting properties)

-         Correct Fuse selection will ensure that the prospective fault currents will be below the cable fault rating

-         Current limiting MCB are very expensive compared to fuses

-         The battery spec have been assumed  due to lack of the battery specification. 

-         DC Cables length was assumed to be 3 m Pos. + 3m Neg. Normally installation length between 1-2 meter

Thank you Alex, I've bought another 6 meters of 25mm cable to double up just to be on the save side and to get COC on my installation. 

 

On 2021/04/21 at 1:44 PM, Alex Feldmann said:

 Ensure Correct SCPD i.e. Fuse are selected

@Alex Feldmann how do I calculate the fuse rating on my battery bank and Solar panles? 4 x 200Ah gel batteries and then again the panels 8s x 300w.  VOC 10A -  iSC 43v  -  Vmpp  36V  - impp 8.33A

Panels fuses 32A?

I was given 32A for panels

@KoppiesThe Growatt es 5kW is allowed to overload (5s@≥150% load)

 5kW x1.5 = 7.5kW for 5 seconds. Which is 156.25A @48V from a battery current perspective.

7.5kW / 48V = 156.25A

I would install a 150A fuse.

 

Edited June 16, 20215 yr by Alex Feldmann

@KoppiesThe solar panels are all in series, so if you look at the nameplate data on the panels, select the max fuse rating specified on the nameplate. Typical rating could be 15A.

E.g. If the panels were 2P4S then 30A would be applicable

 

@Koppies

Correction to the above battery fuse sizing

Scenario 2

If the inverter is overloaded for 10s@110%~150% load then the battery current at 10% 5500W = 114.6A

Scenario 1

 for an overload of 5s@≥150% load. (See above)
 

Thus the two scenarios of overload will be protected by a 100A fuse.

 

 

 

 

 

4 minutes ago, Alex Feldmann said:

@Koppies

Correction to the above battery fuse sizing

Scenario 2

If the inverter is overloaded for 10s@110%~150% load then the battery current at 10% 5500W = 114.6A

Scenario 1

 for an overload of 5s@≥150% load. (See above)
 

Thus the two scenarios of overload will be protected by a 100A fuse.

 

 

 

 

 

Can confirm  the 150% overload.