Configuring the Classic for Battery Cable Voltage Drop?

[finalman]

Just wondering are there any settings that should be set in the classic's menu to compensate for the voltage drop that occurs through the battery cables? To compensate for the difference between the voltage at the actual battery bank and at the classic terminals. As well as compensate for voltage and current losses that occur through the cable while the Classic is charging the batteries.

One thing that I can think of do we set the Vbatt setting for the voltage at the actual battery bank or the voltage at the Classic terminals? Does that help at all?

[ClassicCrazy]

There are a few online voltage drop calculators where you can plug in different numbers to design for the right cable size so you won't have too much voltage drop .

There is a way to calibrate the Classic to tweak the voltage so it matches what a meter says - just in case it is off a bit.

How much of a voltage drop do you have on your system that you want to compensate for it ?

Larry

[finalman]

There are a few online voltage drop calculators where you can plug in different numbers to design for the right cable size so you won't have too much voltage drop .

There is a way to calibrate the Classic to tweak the voltage so it matches what a meter says - just in case it is off a bit.

How much of a voltage drop do you have on your system that you want to compensate for it ?

Larry

Yeah I'm currently using http://www.calculator.net/voltage-drop-calculator.html.

My Current cabling system is below 1/10 of a volt but I for safety reasons I'm probably gonna move the bank another say 3m away.

Current System:
Cable Length 2.5m 70mm2 core diameter.
Enters absorb at 49.2V 40A: voltage drop = 0.051v
Exits absorb at 49.2V 5A: voltage drop = 0.0064v

Moved Battery Bank System:
Cable Length 5.5m 70mm2 core diameter.
Enters absorb at 49.2V 40A: voltage drop = 0.11v
Exits absorb at 49.2V 5A: voltage drop = 0.014v

Losses mentioned are not including the losses at fuse holders, breakers and connections.

[ClassicCrazy]

Are you using flooded lead acid batteries ? If so set your absorb and ending amp setpoints and use the specific gravity of the cells to verify that you have it set up so they are 100% full when it goes from absorb to float .  I will assume you have a Whizbang on shunt - that makes monitoring and controlling a lot easier.

Larry

[dgd]

 
Current System:
Cable Length 2.5m 70mm2 core diameter.
Enters absorb at 49.2V 40A: voltage drop = 0.051v
Exits absorb at 49.2V 5A: voltage drop = 0.0064v

Moved Battery Bank System:
Cable Length 5.5m 70mm2 core diameter.
Enters absorb at 49.2V 40A: voltage drop = 0.11v
Exits absorb at 49.2V 5A: voltage drop = 0.014v

Losses mentioned are not including the losses at fuse holders, breakers and connections.

So you are measuring from the actual battery connection to where?
The main +ve bus and -ve bus connections in your DC distribution box/MNDC/Epanel ? as I imagine a 70mm2 cable coud not really terminate elsewhere.
or perhaps the inverter inputs or Classic outputs?
My one metre 90mm2 cables from battery bank goes to MNDC, -ve to Deltec shunt, +ve to 250A breaker, never noticed any significant voltage drop, my Fluke measures none.

I do see 0.07 V drop over 450mm of #4 from MNDC 100A breaker to Classic 150 when working over 80amps. I often wish the Classics had bolt down power terminals instead of those wire squash screw down types so that cables could terminate in decent copper ring connectors.

dgd

[mike90045]

Simply plugging in a correction factor will not do the job properly.  As the current lessens, so does the voltage drop.  When you get to the last 5A or so of current, the voltage differential will be so low, it can be ignored compared to the drop at 80A.

[australsolarier]

i agree with dgd about them connectors in the midnite classic.

they are too small.
if you want to connect thin strand copper wire in those screw down terminals in the midnite in some countries rules say you need an adapter to connect.
biggest size is something like 20mm2 that fits into those mini terminals. (at 96amps you want at least 50mm2 wire)
you cannot apply counter force when you screw down those mini terminals.
for some strange reason the earth terminal is much larger.(for a smaller sized wire)

i found most voltage drop does not come from the wires, but the breakers. (chinese dc breakers are bad in that respect)

i found that voltage drop does create some minor problems in a highly powered 12V system with lifepo4 battery.
for example it can go into absorb at 65% SOC.  (it is not much of a problem for me, the timer is set to 3h and absorb changes to float  at the end ampere level.
it does however level off too early.
keeping it at float when a discharge occurs because of cloud or high usage it takes a very long time to bring it back up to 98/99% SOC. (unless it rebulks)

with the 48 Volt system however the problems described above are much reduced so as not to be much of a problem in my opinion.

to check the battery voltage in my 12v system i have to really go out to the shed and measure the voltage at the battery terminals. unless the whizzbang jr is going at near 0 amps.

[offgridQLD]

Yes that terminal block is something that needs attention on the classic for all the reasons mentioned.

What they need is a row of threaded studs with a flat plate. That way we can use hydraulic crimped terminal lugs and torque a nut down on the stud compressing the lug firmly onto the plate for max surface area, strength and cable diameter acceptance. Just like you see on your inverter's battery terminal inputs or any high amp industrial termination always uses a (threaded stud and Lug) arrangement or a tapped hole in a plate with a bolt through a crimped cable lug.

Not door bell wire poked into speaker terminals ... some of us run 4000w + arrays into our classics.

[BobWhite]

Yes that terminal block is something that needs attention on the classic for all the reasons mentioned.

What they need is a row of threaded studs with a flat plate. That way we can use hydraulic crimped terminal lugs and torque a nut down on the stud compressing the lug firmly onto the plate for max surface area, strength and cable diameter acceptance. Just like you see on your inverter's battery terminal inputs or any high amp industrial termination always uses a (threaded stud and Lug) arrangement or a tapped hole in a plate with a bolt through a crimped cable lug.

Not door bell wire poked into speaker terminals ... some of us run 4000w + arrays into our classics.

I will agree with Kurt on that, but I'm also known for overkill and I'm ok with that becouse I feel comfortable with what I've done in the end.

[zoneblue]

Youll get absolutely no argument from me.

[Westbranch]

++ 1   

[Jacotenente]

Got an idea: Take the Classic's wiring block and put it into the Kid. The Kid's wiring block is pathetic. And the mounting with a faceplate is another weak point. Redesign it to sit flat with mounting holes...and not have to feed battery and PV cables through two holes. Otherwise, the Kid is a great unit.

As for the Classic's wiring block...they are "okay" but I do like the idea of a "standard" post that can accommodate battery terminal lugs with eyelet holes.

Midnite Solar - If I was a manager there and read these comments, I would thank each one of us that comments and provide direct feedback on your products. Good/bad...FWIW, valuable.

Chris

[binkino]

Ohm's law. check it out.

A voltage drop is dependent on the energy you daw.

So, as more energy you draw over a cable, so more the voltage will drop, caused by the resistance of the cable.
Better calculate your cable better.
If you set a difference to high, you might overvoltage your batteries while charging.


meassure at the batterie terminals in the charger, not at the batteries, and compare the reading with the displayed voltage in the classic.
Thats all.

[australsolarier]

binkino

you cannot over charge a battery because of long cables. more likely undercharge. all it means is it might take longer for  a full charge. i don't think it is much of a problem for lead acid batteries. more so for lifpo4's because they are so "stiff". and mostly for 12v systems.

as you near absorb the current lessens and consequently the voltage loss drops. as you near 0 amps the voltage drop disappears altogether.
so much for ohm's law.

most resistance does not come so much from the wires but the breakers. at least that is my experience.

basically there is not much you cannot do besides installing A1 quality breakers. and i would not worry about it too much. unless you are really enthusiastic about it.

so to let you know about my measurements of my 12V system of the voltage drop, from midnite terminals to battery terminals:
0.23V  at 40A
0.40V  at 70A
i estimate about 95% of this voltage drop is from the breakers. as described before this 0.4 voltage drop triggers abosorb in the midnite classic as low as 65% SOC. as it hits the programmed absorb voltage it limits current to the midnite's voltage not the actual battery voltage. so it takes somewhat longer to go to float (full charge)

the 48v system behaves totally differently, the voltage losses there seem not to have such a big influence.