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Thread: Charge Controller - Load Connection

  1. #1

    Default Charge Controller - Load Connection

    So I'm shopping for a better charge controller... Something in the area of 20-30 amps/12 or 24v/PWM.

    Here's my question:

    If a charge controller has a "load" port... Does this mean the max load going through that port is the max load of the charge controller (usually indicates the max input)?

    Also, what is your preference; charge controller with or without load port? I noticed on some controllers with the load port, you really cant use a thick cable from the battery...


    Thanks in advance,

  2. #2
    Join Date
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    Default Re: Charge Controller - Load Connection

    i believe you are referring to the low voltage disconnect (lvd) and at most i believe that it is around 10a draw. it will switch out the load if the voltage dips real low, but by then you've pretty well drained that battery anyway. you are correct that it is limited in its wire size abilities. we usually tap the battery with a good gauge wire and proper fusing.

    hmmm, i'm confused because you are shopping for a "better charge controller" and are going to pwm controllers so what do you have now that the pwm is a step up? i prefer the series type controllers rather than the shunt type. the series type will just act like a switch closing when power is needed, but a shunt type sends the power to ground until needed so it is constantly loaded and producing heat. if the shunt fails all power goes to the load while if a series fails the circuit opens.
    NIEL

  3. #3

    Default Re: Charge Controller - Load Connection

    Niel: I'm referring to the load connection on a charge controller. So you have I have three connections on this controller, 1. Solar Panels, 2. Load and 3. Batteries.

    My question is simply; If my charge controller says it can handle 10 amps max.. does this mean that input AND output (load) must be under 10amps? OR does this mean that only the input is limited to 10 amps? Not to sure about this 'LVD' you're talking about.

    Oh, and my current CC is a 10amp PWV CC. What I meant to say was I want to upgrade this CC to one that can take more amps.

  4. #4
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    Default Re: Charge Controller - Load Connection

    Quote Originally Posted by SolaRAC View Post
    Niel: I'm referring to the load connection on a charge controller. So you have I have three connections on this controller, 1. Solar Panels, 2. Load and 3. Batteries.

    My question is simply; If my charge controller says it can handle 10 amps max.. does this mean that input AND output (load) must be under 10amps? OR does this mean that only the input is limited to 10 amps? Not to sure about this 'LVD' you're talking about.
    The answer to your question is no. Please re-read Niel's response as he explains it well. Some rather low end controllers have a "load" terminal that might be used for a couple of lights or whatever, and are turned "on" under conditions determined by the controller manufacturer and possible customer settings, and should be explained in the owners manual. The more common thing is a LVD (Low battery Voltage Disconnect) connection, which is often how the so-called "load" output is configured to work.
    1900 watts PV, (1000 watts PV feeding MidNite Classic 150; 900 watts PV + 160 watts micro hydro both feeding into a single shared Morningstar TS-MPPT-60) ; Xantrex Pure Sine 1800/12 for heavy loads; Xantrex Pure Sine 1000/12 on 24/7 for everything else; six Rolls Surrette 2 volt L16 @ 12 volts.
    Domestic hot water totally provided by the sun 8 months out of every year via thermal panel.

  5. #5

    Default Re: Charge Controller - Load Connection

    In the case of the small Morningstar and Steca PWM CCs the PV in and the Load out have the same current rating. This means that if you have properly sized your battery circuit wiring for the controller's PV rating it is also properly sized for the controller's DC load rating. There are some exceptions for specific models. Below is a a SunSaver Spec sheet which shows PV and Load ratings are the same for all but the smallest unit:
    http://lib.store.yahoo.net/lib/wind-sun/sunsaver.pdf


    Not all PV/Load controllers are designed with the same logic or programmable for your desired DOD. Some are intended to be "lighting" controllers which do not turn on the load until dark. They also may have a fairly low Low Voltage Disconnect (LVD) setting, (+/-11.5 for example) which may be fine if your load is large enough to pull the battery voltage down enough while the DOD is still at a reasonable level. If your loads are very light, however, your DOD can get very low before the voltage falls enough to trigger the LVD setting.

    If you need to increase the wire size for longer distance load wiring runs or if you are trying to provide an adjustable LVD circuit for a DC load panel (30-60 amps) you may want to look at the Xantrex C-series controllers in "Load Control" LVD mode. They accept up to AWG #2 wire. If you go this route, you will still need a seperate controller for the PV.

    Alex Aragon
    Last edited by SolaRevolution; April 29th, 2012 at 10:57 PDT. Reason: Add increased load wiring for long distance runs

  6. #6

    Default Re: Charge Controller - Load Connection

    It all makes sense now.

    I do alot of video searches on youtube and saw alot of people connecting their battery bank directly to the inverters. Is LVD also a common feature for inverters (ie built in LVD)?
    Whats your preference either way? Battery to CC or battery to Inverter? Or is it 'Whereever the LVD is'?


    Thanks,

  7. #7
    Join Date
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    Default Re: Charge Controller - Load Connection

    Inverters typically have LVD function built in... Typically around 10.5 volts for a 12 volt inverter.

    The LVD is not really to protect the battery bank, but to protect the inverter instead. Inverters are constant power devices--P=I*V

    With constant power output (your AC load), and falling battery voltage (from ~15 volts high to 10.5 volts low), I must increase in order to meet the demands of the load. If the battery voltage falls too low, the inverter could otherwise be damaged by too much current and overheat.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  8. #8

    Default Re: Charge Controller - Load Connection

    I was looking forward to using this feature to prevent my battery bank from going beyond 50% DOD.

    If I understand you correctly, are saying saying I shouldnt rely on a customizable LVD?

  9. #9
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    Default Re: Charge Controller - Load Connection

    Yep--Measuring Battery Voltage is very inaccurate during charging and discharging cycles as an estimate of state of charge (also varies with battery bank temperature too).

    If you want/are able to set an LVD/Alarm based on voltage--You can start with ~11.5 volts as the floor and see what happens (many LVD's have a timer too--like 1/2 a minute to 10 minutes or so below set point).

    A Battery Monitor (Victron is another brand with some happy users here too) is much better at ESTIMATING state of charge while the battery is under charge/discharge. However--They do drift and typically reliy on some conditions to reset back to 100% capacity (like 14.5 volts for more than 2 hours, etc.).

    While there are a few monitors that estimate state of charge via voltage only--Most "true" battery monitors put a shunt in the negative/return lead of the battery bank to measure total Amps*Hours in/out of the battery bank (against your programmed AH capacity and various "models/parameters" in the battery monitor CPU.

    MidNite Solar MNBCM Battery Capacity Meter
    www.smartgauge.co.uk

    The Midnite, for example, will tell you if your battery bank has not had a "full charge" in the last few days (good for warning of possible system problems).

    A few Battery Monitors (Xantrex and Victron are two that I am aware of) have a programmable external contact that you can connect to "something" if your battery bank is below (for example 50%) a set state of charge. It could set an alarm, start a generator, turn off an inverter, etc.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #10

    Default Re: Charge Controller - Load Connection

    Quote Originally Posted by SolaRAC View Post
    I was looking forward to using this feature to prevent my battery bank from going beyond 50% DOD.

    If I understand you correctly, are saying saying I shouldnt rely on a customizable LVD?
    The customizable LVD is what you want to protect your batteries.

    The ProWatt SW has a preset 10.5 LVD. Very low for the sake of protecting batteries. It may help protect them if your loads are 20% of the battery capacity. If you're trying to protect against deep discharge caused by light loads such as inverter idle current, I'm afraid that 10.5v will be way too late.

    The 60 amp C-series controller will only handle 60 amps at the battery voltage. If you go as low as 11.5vdc this would only be 690 watts for your inverter input. Less at 90% efficiency for the output. I'm not too sure about the surge capabilities of the C-series in Load Control mode. I've used the Morning Star 300watt inverter with a C-40 successfully.

    Alas, these issues are not usually adequately addressed until you get into the more expensive, fully programmable range of inverters.

    I suggest you be sure your inverter is disconnected from the battery when you leave. (not just off at the inverter's on/off switch.) And keep the charge controller and PV on with proper settings and temp comp.

    Alex Aragon

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