Battery DC Disconnect?

quiquequique Solar Expert Posts: 252 ✭✭
I have a 6 battery bank. Each battery is 6V so I connected each pair in series. Then each 12v pair (which i checked and they are 12V) is then connected in parallel pos-pos-pos and neg-neg-neg.

Attachment not found.

My question is, I had this plan to add a DC Disconnect between the solar panels and the battery bank as I've seen in my textbooks.

But I ended up adding the DC disconnect between the cables that run from the ChargeController to the BatteryBank.

I was about to disconnect it when I started thinking if I may want to leave it there anyway. The weird thing is that I tested the voltage between the + DC DISCONNECT BOX && - CC-to-battery lead and I got a 12V reading whether the breaker is up or down. Why is that?

Comments

  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Battery DC Disconnect?
    quique wrote: »
    I tested the voltage between the + DC DISCONNECT BOX && - CC-to-battery lead

    Which side of the disconnect box did you measure - Battery or CC?
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery DC Disconnect?

    I put the

    >>> neg tester lead on the CC's out to battery bank negative &

    >>> pos tester lead on the DC disconnect panel pos incoming cable from the battery bank

    oh wait...that makes sense...the disconnect only occurs at the bottom of the breaker, not in the incoming top part of the breaker!
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Battery DC Disconnect?
    quique wrote: »
    I have a 6 battery bank. Each battery is 6V so I connected each pair in series. Then each 12v pair (which i checked and they are 12V) is then connected in parallel pos-pos-pos and neg-neg-neg.

    My question is, I had this plan to add a DC Disconnect between the solar panels and the battery bank as I've seen in my textbooks.

    But I ended up adding the DC disconnect between the cables that run from the ChargeController to the BatteryBank.

    If your batteries are hooked up as shown in your diagram, they will be short lived. The current to each of your strings passes through a different length of cable. That will exacerbate all the other issues that come up with parallel batteries.

    I don't know which charge controller you have, but disconnecting the battery while leaving the PV connected can damage some of them.

    You should have a circuit breaker (which can serve as a disconnect) between the battery and the charge controller. (actually, you should have a circuit breaker between the battery and anything and everything connected to the battery).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery DC Disconnect?

    Ok so #1: the battery to CC dc disconnect is fine. I just need to continue and add my pv-CC dc disconnect.

    As for #2: how should they be wired then? I don't see different length cables. Could you help me out?
  • animattanimatt Solar Expert Posts: 295 ✭✭✭
    Re: Battery DC Disconnect?

    Attachment not found. I did a quick edit of your diagram. This is more in line. Other can explain more in depth.

    matthew
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery DC Disconnect?

    In this case you have three parallel battery strings. Not the best idea because of the current sharing problems which may arise and will be particularly noticeable on a 12 Volt system.

    Enter the Smart Gauge diagrams: http://www.smartgauge.co.uk/batt_con.html

    For three parallel strings you should be using Method #3; each battery string connected through equal length wiring to common connection point. Ideally each string will have its own post terminal fuse as well.
    The weird thing is that I tested the voltage between the + DC DISCONNECT BOX && - CC-to-battery lead and I got a 12V reading whether the breaker is up or down. Why is that?

    This is not unusual. Charge controllers have circuitry in them that can retain Voltage even after the battery is disconnected. As such with the negative common you will read +12 VDC on the battery side and +12 VDC on the controller side even though the positive connection between the two is broken. If you wait long enough the Voltage in the controller will dissipate, providing it is not being replenished by batteries or PV.

    It is normal to have a disconnect on the PV side and the battery side, depending on the controller used. The PV disconnect is not essential as it is fairly easy to kill their output by covering or waiting for dark, making it safe to pull a wire and do whatever work is needed. Battery side always has power on it so it's best to disconnect this with a switch or breaker. The breaker will provide both disconnect function and over-current protection.

    Most of the time you will never have to disconnect anything; once it's working it should stay working. :D
  • quiquequique Solar Expert Posts: 252 ✭✭
    Re: Battery DC Disconnect?

    Antimatt:

    So you are taking the neg from the top and the pos from the bottom? That's the only difference?

    Caribocoot:

    Method 3 in that page would give me a 6v bbank. I guess what you mean was that I leave my 3 series pairs as is, and then wire all positives to a common point and all negatives to a common point and then go to the inverter?

    Like this:

    Attachment not found.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery DC Disconnect?

    The methods shown on the Smart Gauge site assume individual batteries. It does not matter is you connect two 6 Volt batteries in series to make a 12 Volt battery: essentially all these batteries are individual 2 Volt cells anyway.

    This drawing shows the same type of wiring method but with two parallel strings of two batteries in series each.
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