Cable Connections: Battery Bank

TexasOffGrid · April 2017

I recently added two more batteries to my VmaxTank battery bank, now having 6-Batteries in a parallel/series configuration. I have 6, 12-volt batteries wired for 24V. I can't seem to find any description of how to connect my charge controller to this battery bank? Some diagrams show connection the +, - cables at the end of the array, some show the +, - cables splitting the array at each end. Does the charge controller care? I think I just burned out my EPSolar Charge controller and just ordered the Midnight kid to replace it. Help

mcgivor · April 2017

Vmax tank battery!?? What is that? You need to give more information such as Ah ratings flooded or AGM etcetera , sounds like 3 strings of 2 in series, adding new? batteries to older ones? is not the best thing to do, why all the question marks? Details, the more the better.Edit. You are new to the forum, welcome, hope we all can help.

BB. · April 2017

Here is a quick wiring diagram:

http://www.smartgauge.co.uk/batt_con.html

There are several ways to connect to the battery bank--Basically, you want the same length of wiring from the load/charging connection to the batteries. If you have more resistance (longer wiring) to one set of batteries vs another set, the higher resistance will prevent the "remote set" from properly supporting your loads/getting proper charging voltage/current.

When you are working with Lead Acid and larger battery banks, you want to have proper circuit breakers/fuses between the batteries and your loads... Even a relatively small battery bank can supply 100's to 1,000's of amperes into a dead short and start a fire.

-Bill

TexasOffGrid · April 2017

Thanks for the quick response. Apology for not being specific. They are AGM batteries, all of the same load, and design. Maybe this picture will be more descriptive: Does this look correct? Thank You.

Image: https://us.v-cdn.net/6024911/uploads/editor/gj/zqpwmvkw2efh.png

BB. · April 2017

What will the charging current and load current be? I.e.;

30 amps * 0.80 NEC derating for continuous current for Breaker/Branch circuit wiring = 24 amps max continuous charging current
200 amps * 21.0 volts battery cut off * 0.85 AC inverter eff * 0.80 NEC derating = 2,856 Watts (VA) max recommended AC inverter load

In general, the leads from the charge controller to the battery bank and from the AC inverter to the battery bank should be kept very short and run in parallel ("looping" wiring can emit radio interference and pick up lightning/static discharge interference).
-Bill

jonr · April 2017

With 465 AH of battery in most situations/batteries, I'd want to charge at more than 46.5A + loads. And even then I'd check that they were getting fully charged on a weekly basis. Consider a second Midnite Kid + panels to match.

I would use "method 3" (see link above) and use a clamp on DC RMS ammeter to check/adjust balance. Even more so with a mix of old and new batteries.

bsolar · April 2017

my system 'was' wired like your diagram, it works ok .. the problem with that scenario long term is what the other guy was talking about and thats keeping the batteries in a balanced state .. its next to impossible to keep the loads and charge rate the same across all the batts because current will take the easiest path like water downhill, and once you wind up with a low batt or two in the bank it gets detrimental to their health pretty quick .. if it were me, i would keep the system configured so you can easily take down the wiring, monitor and charge the batts at least in pairs, run them through a load/charge cycle once a month like that to keep an eye on them ..

TexasOffGrid · April 2017

Thank you for the feedback. The system seemed to be working okay for a few days, but my 30 AMP fuse from the charge controller to the battery blew.....and then a few days later blew again. I was worried that the charging cables were hooked up at the wrong ends. Currently using the Tracer 3215RN (30 AMP) charge controller. Perhaps I need a 40AMP controller?

westbranch · April 2017

Do you have a DC clamp meter to measure the Amps in each cable? that will tell you which string is going high...

TexasOffGrid · April 2017

No, do not have a clamp meter....I guess I need to get one though.

BB. · April 2017

Here is one that is "Good Enough" for our needs. Only $60:

http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

-Bill

Horsefly · April 2017

This one is also a good one, and has a "Max" feature that managed to capture the inrush current for our well pump. That feature is really handy, and not common in cheap clamp meters.

https://www.amazon.com/gp/product/B019CY4FB4

jonr · April 2017

As Bill explains, you don't want to run 30 amps through a 30 amp breaker or fuse.

BB. · April 2017

30 amps x 1.25 nec derating = 37.5 amps ~ 40 amp breaker + wiring minimum rating

- Bill

mcgivor · April 2017

To add to the above, it is important to understand that the purpose of an overcurrent protection device, be it a fuse or circuit breaker, is to protect the conductors downstream in the event of an overcurrent event such as a short, not to protect the device being fed. Another point to keep in mind is generally breakers and fuses rated for AC do not work for DC, with a few exceptions, make sure they are DC rated if used on DC circuits.

TexasOffGrid · April 2017

Thank you for the advice and comment. I have ordered the Amazon Ammeter to check current levels. I guess I'm still confused over how my 30-Amp Charge Controller can generate more than 30 Amps when charging the batteries and blow my 30-amp fuse? I understand the the math from Bill....but I am running 6 AWG wire from the charge controller to the Battery (less than 4 feet). Am I getting current flow back to the controller? What's really happening on my pictured setup? Thank you.

jonr · April 2017

The charge controller isn't producing more than 30 amps, it's that the 30 amp fuse is really less than 30 amps.

TexasOffGrid · April 2017

Okay....so i ordered some 40AMP fuses...any risk of fire if I replace the 30AMP with a 40? the 6 AWG wire should handle the load, right?

mcgivor · April 2017

The current rating for 6 Awg copper is 55A thereabouts, depending on insulation rating, ambient temperature, in a raceway, or free air, but for your situation a 40A fuse would be reasonable choice, personally I prefer fuses, others may disagree, as it's handy to have a means of disconnect and protection in one package with a circuit breaker.

TexasOffGrid · April 2017

Well, I finally got my Midnight Kid charge controller hooked up. With the inverter switched off, the batteries seem to charge evenly. When I turn on the inverter (under the setup depicted above), the "Kid" amperage starts to jump all around, occasionally hitting over 30AMPS and giving me an over-voltage fault on the "Kid" charge controller???? I must be getting feedback from the inverter when it is pulling power? Appreciate any thoughts on this. IS there a better way to hook up the charge controller to the battery bank? Thank You.

jonr · April 2017

What type of load is on the inverter when this happens?

mcgivor · April 2017

What is the array size and configuration, there was no previous mention, but it sounds like inverter load is promoting the CC to make up the deficit but the array can supply more than the CC can handle. Just theroy, a detailed description including full panel specs and array configuration would be helpful to those who would like to help.

TexasOffGrid · April 2017

I included another picture with the array specs. I have a Go-Power 3000 watt pure-sine wave inverter that powers two freezers (1.2A and 1.7A). The system worked great when I only had 4 batteries in the bank...I added two more to make six (all the same batteries and AH rating, and that is when my problems started....not sure why, unless the CC leads need to placed differently? Really appreciate the help!

Image: https://us.v-cdn.net/6024911/uploads/editor/fr/mvv0zgpuej0j.jpg

mcgivor · April 2017

There have been two changes, the additional batteries and a replacement CC, is this correct? Your wiring according to the diagram looks good, array wise, perhaps 3 panels in series 2 strings parallel would be better, more head room for the MPPT to operate efficiently, just an observation, perhaps someone with MS Kid experience could have some input.

Estragon · April 2017

Overvoltage on the CC? It looks like pv is 3 strings of 2 panels. Combined should be ~36Voc and 15a. The kid handles much higher voltage.

Did you connect the kid to the batteries first and to the pv after? Is it set for any sort of load diversion. Any chance you connected the batteries to the load terminals on the kid (not a hard mistake to make).

I would also recheck and retorque all connections. They can get surprisingly loose with cold flow in the day or so after initial connection.

TexasOffGrid · April 2017

Thanks to both mcgivor and Estragon. Yes, connected the batteries first and pv after. Connections are in accordance with the Kid set up manual, on the right terminals. The Kid is charging the batteries just fine...then when I turn on the inverter, the amps on the Kid display start jumping all over the place, spiking above 30 at times....I am bewildered.

jonr · April 2017

Does the problem not occur when the freezers remain off? Long shot, but I'm thinking a reactive load putting pulses of power back into the batteries, causing a battery over-voltage (vs over voltage on the PV side). And confusing the Kid about charge level.

Estragon · April 2017

Just to clarify - in your original post you said the kid had an overvoltage fault, but amps > 30 in last post would be overcurrent.

Have you tried plugging in the reefers one at a time (with the inverter already on). What does the kid read with the inverter on but with no load, and with each of the reefers plugged in separately in turn.

Also, when doing this, don't unplug and plug back in right away. Short cycling can cause back pressure - increased start load.

mcgivor · April 2017

Additionally if an inverter is left off for a period of time, the capacitors will discharge, the switching on will take a bite out of the battery, then two refrigerators stating together may sag the battery voltage and confuse the CC momentarily, once running dose everything settle down?

Estragon · April 2017

I was wondering about inverter startup as well. My Outbacks take 30sec or so to charge. BTW, did the breaker issue get sorted out? I wonder if related?

Estragon · April 2017

Also, I assume the reefers run ok with the inverter running off battery and no solar?

Cable Connections: Battery Bank

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