earthrealm:


who has clamp meter for sale??...my present unit has started having a reading of 36amps..just lying down in its case , need a new unit asap

Malevonent:


Ok will double ch3ck th3 connections..they r all 16mm. Half yard each..my 5kva inverter was displaying 15% load...and had solar input of abt 330w 48v setup ..would the solar input be capable of introducing errors?...

chris81964:


Do your cables get hot when charging? 16MM in my opinion is too thin. Just my opinion.

NiyiOmoIyunade:
If the battery interconnect cables get hot while charging or discharging then very definitely he needs to upgrade to a thicker gauge.

16mm is roughly 5 to 6awg per US measurements - per the NEC (US National Electric Code) Ampacities table, 16MM ( 5 to 6awg) is good for approx ~60amps at 60°C. If OP is charging or discharging under 50amps at 48v nominal and with the short cable lengths (half a yard) he mentioned then 16mm is well within spec.

I have attached the NEC Ampacities guide below

http://www.usawire-cable.com/pdfs/nec%20ampacities.pdf

I am sure that the NEC guide is a good guide. Our experiences however don't support the recommendations or suggestions that they make. Cable quality varies so much that we play it safe and go thicker. If his cables don't get hot when he charges then he is fine.

Malevonent:

Ok will double ch3ck th3 connections..they r all 16mm. Half yard each..my 5kva inverter was displaying 15% load...and had solar input of abt 330w 48v setup ..would the solar input be capable of introducing errors?...

NiyiOmoIyunade:
If the battery interconnect cables get hot while charging or discharging then very definitely he needs to upgrade to a thicker gauge.

.... then 16mm is well within spec.

I have attached the NEC Ampacities guide below

http://www.usawire-cable.com/pdfs/nec%20ampacities.pdf

Saipro:


You might want to upgrade to at least 35mm² cables for battery interconnects if they're 200AH or higher. The resistance (impedance) becomes nearly negligible at those gauge sizes. I generally don't use below 50mm² for ease of mind. I suggest you do the same

chris81964:


I am sure that the NEC guide is a good guide. Our experiences however don't support the recommendations or suggestions that they make. Cable quality varies so much that we play it safe and go thicker. If his cables don't get hot when he charges then he is fine.

Saipro:

Your advice is on point yet unsafe in this scenario.

They'll get warm if he's using the C10 charge rate, even if 25mm² and the distance is as short as manageable. And molten battery terminals/posts are real. Ask the victims.

Saipro:


You might want to upgrade to at least 35mm² cables for battery interconnects if they're 200AH or higher. The resistance (impedance) becomes nearly negligible at those gauge sizes. I generally don't use below 50mm² for ease of mind. I suggest you do the same

NiyiOmoIyunade:
My Oga,

I have used 16mm cables for years for battery interconnects in 48v 200Ah systems with no trouble. The cables are always full gauge copper and typically inverter charge amps max out at 30a/40a.

Where i have solar added on, I typically use 35MM cable from CC to battery and battery interconnects especially in a large PV array that may gross 60a output.

I am convinced I am over designing in these cases but better safe than sorry and thicker cables can do no harm afterall.

With the MustPower type inverters, I have observed battery cables get warm from around 45a/50a as the charger output seems to have a lot of AC ripple or other noise in the signal (I have yet to verify this empirically). With a clean DC signal such as a charge controller may put out, the cables stay cool at the ~50a range.

NiyiOmoIyunade:
Let me guess UniT or Mastech? or some other El- Cheapo knockoff meter?

chris81964:


Do your cables get hot when charging? 16MM in my opinion is too thin. Just my opinion.

Malevonent:


i used this to check prior to purchase, http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
the site above confirmed that 16mm is ok.
installer recommended 35mm truout, i refused. i used 35mm for just inverter to battery, 25mm for cc to battery - all about 2.5m

hvnt really bothered to chk if it gets hots when charging, will do so and revert.

NiyiOmoIyunade:
In your average use scenario for Nigeria, a user has 4 12v 200Ah batteries to make his 48v 200Ah system, if he has a 5kva inverter connected to the bank, he either chose it because that was the only or cheapest size available for 48v or he wanted the relatively faster charging (with limited Mains or Gen availability) or because he was told the inverter was 'rugged' enough to carry his freezer or fridge and it would 'last' or some other reason not related to the actual performance characteristics of a 5kva inverter.

The inverter in question would have on average less than 1kw of total loads connected to its output - my point is that your average user purchases a 3.5kva Sukam or 5kva Felicity because that is the smallest 48v choice he has - he doesn't really need or use that 5kva capacity neither do the connected loads ever even approach that 5kva limit.

Come to think of it, why would someone even try to put 2kw+ of loads on a 9.6kwh bank (4 pcs 12v 200Ah batteries) on a routine basis?

The above is the design scenario where people use 16MM cables for battery interconnects and it more than suffices - millions of Nigerians do it this way and have managed to get by with no trouble for years.

Unlike hardcore users on here who want to routinely load a 5kw rated inverter with 4.8kw of total loads, that is simply not the case for 99% of users who have that same size inverter and a much undersized battery bank relative to the inverter capacity.

To be frank, most users or installers do not even have the tools to properly crimp on lugs onto a 16mm cable (they just use a plier) not to talk of 35mm or 50mm cables which are much thicker and tougher to work with without proper tools.

I would be surprised (nay flabbermoosed) if it turns out inadequate cable gauge is the culprit behind OP's battery balance issues but let us wait to hear from him. Anything is possible afterall.

NiyiOmoIyunade:
In your average use scenario for Nigeria, a user has 4 12v 200Ah batteries to make his 48v 200Ah system, if he has a 5kva inverter connected to the bank, he either chose it because that was the only or cheapest size available for 48v or he wanted the relatively faster charging (with limited Mains or Gen availability) or because he was told the inverter was 'rugged' enough to carry his freezer or fridge and it would 'last' or some other reason not related to the actual performance characteristics of a 5kva inverter.

The inverter in question would have on average less than 1kw of total loads connected to its output - my point is that your average user purchases a 3.5kva Sukam or 5kva Felicity because that is the smallest 48v choice he has - he doesn't really need or use that 5kva capacity neither do the connected loads ever even approach that 5kva limit.

Come to think of it, why would someone even try to put 2kw+ of loads on a 9.6kwh bank (4 pcs 12v 200Ah batteries) on a routine basis?

The above is the design scenario where people use 16MM cables for battery interconnects and it more than suffices - millions of Nigerians do it this way and have managed to get by with no trouble for years.

Unlike hardcore users on here who want to routinely load a 5kw rated inverter with 4.8kw of total loads, that is simply not the case for 99% of users who have that same size inverter and a much undersized battery bank relative to the inverter capacity.

To be frank, most users or installers do not even have the tools to properly crimp on lugs onto a 16mm cable (they just use a plier) not to talk of 35mm or 50mm cables which are much thicker and tougher to work with without proper tools.

I would be surprised (nay flabbermoosed) if it turns out inadequate cable gauge is the culprit behind OP's battery balance issues but let us wait to hear from him. Anything is possible afterall.

Wazari:
While I understand what you are trying to say, I don't think it is good practice to spec the cables based on the present consumption or the battery bank size. You should use the inverter norminal rating. So in this case, we are looking at approximately 105A for a 5kva 48V inverter. The reason is that even though you know the present power demand, you cannot predict what will be plugged into the inverter in future. Most inverter manufacturers provide a recommended cable size in their manuals for this reason.

So from your NEC table, the cable minimum size should be either 3AWG (90C) or 2AWG (75C). In either case, the minimum cable size will be 35mm.

That said, like you said its too early to say if the cable gauge is the reason for battery balance issues.

pranil:


I agree
for four batteries the inverter is probably 5 KW for 5 KW at least 35 or better 50 mm2.

Can you detail the inverter.CC make model, please

My guess is the batteries are not getting correct voltage due to cable loss. Does the inverter CC have voltage compensation and direct voltage measurement otherwise the batteries may be getting undercharged? a regular undercharging will prevent them from absorb stage

A simple test will be to measure the voltage at battery terminals while under full charging current ( near the end of charging) and check with manufacturers spec.

If lower you need to raise charger ( inverter/CC) setpoint

S007:


Great comment. I concur. Most manuals will also tell to you to go higher if cable length will be an issue.

earthrealm:


Bought it on amazon

duwdu:


Whoa... the bit in bold+italics is in fact what I've been practicing... I happened to have noticed that, with my PCM60X CC manually and properly set-up for charging my AGM batteries:

1.) With the recommended and supplied Battery Voltage-Sensing cable connected, 29.2V (@24V nominal) on the CC actually reads only 28.2V on my VIL Power Star-Light 3KW inverter, 28.2V on a clamp multi-meter, and 28.0V on my proper multi-meter which I trust more because the accuracy of it's readings has been favorably compared to those on Flukes. I ascertained these discrepancies consistently over one or two charge cycles.

2.) Without the BVS cables, the CC @ 28.6V would give 28.2V, 28.2V, and 28.0V respectively as listed under 1., above. This indicated to me, that the CC was potentially undercharging my batteries! So,

3.) I've settled to NO LONGER use the BVS cable, and for the CC maximum absorb charge @ 29.7V; the other measurements now register max 29.4V, 29.4, and 29.1-2V, respectively. I calibrated the CC's Float charging parameters accordingly.

My batteries are maintained at under 30 degrees Centigrade almost always, as measured with an ETEKCITY Lasergrip 774 Infrared Thermometer.

If I'm correct in my above steps, then many thanks to the lessons and confidence imparted on me on this forum and elsewhere, otherwise I welcome all corrections, advice, and criticisms. Thanks.

........
P34c3
.....
...

Malevonent:


i used this to check prior to purchase, http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
the site above confirmed that 16mm is ok.
installer recommended 35mm truout, i refused. i used 35mm for just inverter to battery, 25mm for cc to battery - all about 2.5m

hvnt really bothered to chk if it gets hots when charging, will do so and revert.

NiyiOmoIyunade:
I am a fan of using the thickest gauge cable you can possibly afford for best results but I will also be the last to say a particular cable size is insufficient when it clearly is sufficient for the application and many authorities that set building and electrical codes aver that it is sufficient.

It is much like a friend who ran 4MM wires to all sockets in his house to power his 2hp ACs which came from factory installed with 2.5mm wire or people who dedicate a 5kva relay stabilizer to power their 'large' chest freezer whose maximum possible surge watts is about 1.5kw and running watts under 300w - sure these will work without issues but they are both clear cases of overdesign.

....

If in doubt, then it is best to go for the next higher cable size like we have all reinforced several times.

Saipro:

Once again, you're right but ... distance matters (resistance is quoted per unit distance) and you never can trust the quality of your cables.

I have a 15kVA servo AVR and 4mm (calculations as per requirements specs showed 2.5mm) should be more than sufficient a gauge of cable to run power to and from it under 1m of distance.

I did the installation myself using best practices as guidelines. Lo and behold, my 10mm cables got quite warm at 6kVA loading (on the input side of the servo). And that's AC, not DC.

The point being, you really can't be too careful. And yes, time and time again, people have shown wanton use with big inverters. Rather than the 99% you quoted, I'd say more like 30%. AbuNafiu and Kiekie1 can bear witness to this. I'll merely assume you've had very civil and obedient clients thus far.

pranil:


did you try pressing zero button for 3 sec while keeping it away from any electrical field ( and jaws closed)

DC tong testers need zero calibration on every start

Saipro:

Once again, you're right but ... distance matters (resistance is quoted per unit distance) and you never can trust the quality of your cables.

I have a 15kVA servo AVR and 4mm (calculations as per requirements specs showed 2.5mm) should be more than sufficient a gauge of cable to run power to and from it under 1m of distance.

I did the installation myself using best practices as guidelines. Lo and behold, my 10mm cables got quite warm at 6kVA loading (on the input side of the servo). And that's AC, not DC.

The point being, you really can't be too careful. And yes, time and time again, people have shown wanton use with big inverters. Rather than the 99% you quoted, I'd say more like 30%. AbuNafiu and Kiekie1 can bear witness to this. I'll merely assume you've had very civil and obedient clients thus far.

chris81964:


All your battery cables should be the same size. From inverter to battery and between batteries. Everyone including me has got an opinion. You should not be surprised then that your batteries are not behaving. You did not listen to the installer.