help needed for charge controllers

Hi there,

I am from Pakistan. I have a little technical question related to connecting charge controllers in series.

Currently I have 2 charge controllers. one is of 48V and other is of 12/24V. I want to know is it possible to connect these controllers in series to get 72v charge controller?

And if no, can I connect three cheap charge controllers of 12/24v in series to get 72v charge controller?

If both of situations are not possible, then what cheap solution is possible to cut battery charging when batteries are full?

Thanks in Advance

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: help needed for charge controllers

    Welcome to the forum.

    Connecting charge controllers literally in series is asking for trouble. This is because the negative side of most of them is "through put" (the same on the in as the out) and as such it becomes all too easy to create as short across one and the battery it is connected to.

    In order to do it, the PV on each controller must be kept entirely isolated for both negative and positive from the other controllers. The output would be made to the batter bank at the corresponding Voltage points, not strung together so that one controller connects to (-) on the bank and another to (+).

    Using different controllers at different Voltages to divide up the bank is bound to produce uneven results too. It is possible, for example, to do this with a 36 Volt bank charging each 12 Volt 'section' with identical panels & controllers. If you were to do the same for your 72 Volts it would be three 24 Volt arrays and controllers.

    72 Volts is an unusual Voltage, may I ask what this is for?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: help needed for charge controllers
    72 Volts is an unusual Voltage, may I ask what this is for?

    I'm also curious to know what you do with 72 volts. Since you can't usually put charge controllers in series, you might consider a Midnite Classic charge controller which can charge 72 volt battery banks.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: help needed for charge controllers
    Badar wrote: »
    Currently I have 2 charge controllers. one is of 48V and other is of 12/24V. I want to know is it possible to connect these controllers in series to get 72v charge controller?

    Generally won't work for several reasons, including that neither controller will see the battery's actual (or even divided) voltage once the other one opens (or throttles.)
    If both of situations are not possible, then what cheap solution is possible to cut battery charging when batteries are full?

    For low cost use a simple relay with a voltage comparator. When the voltage is over the battery's maximum charge voltage, open the relay for a short but fixed time.
  • BadarBadar Solar Expert Posts: 38
    Re: help needed for charge controllers

    I am sorry I didn't explain my objective very clearly.

    heheheh it is actually little stupidity involved.

    Actually I have 1600 watt solar panels installed on my home. Originally it was 12v system i.e. with single battery and a 12v UPS (Inverter).
    After few months I shifted it to 24v system i.e. solar system with 2 batteries and a 24v UPS (Inverter).
    Charge controller used in both of above cases was 12/24v auto detect. A simple PWM charge conroller.

    This year I shifted it to 48v system i.e. system with 4 batteries and a 48v (1500Kva) UPS. I purchased used Tarom 48v Charge controller.

    But now I am interested to expand my solar system so that it could be capable enough to power my whole electric system in day time.
    I am interested to purchase a used MGE 3200 Pulsar EXtreme Inverter from market. its almost free i.e in just PKR 15000/- (US $15)
    It operates on 6 batteries. I will purchase 6 new Lead-acid batteries and modify this inverter to use these batteries.

    but unfortunately there is no 72v charge controller available in market. So i need to do something.
    I need no high tech charge controller. I just need a controller that can cut battery charging when batteries are full. ( I know importance of MPPT, but I am very well aware of my pocket as well )

    Since I have one 24v and one 48v charge controller, so i read some where that two charge controllers can be used in series.

    Hope you will understand my problem and will help me.

    thanks
  • BadarBadar Solar Expert Posts: 38
    Re: help needed for charge controllers
    Generally won't work for several reasons, including that neither controller will see the battery's actual (or even divided) voltage once the other one opens (or throttles.)



    For low cost use a simple relay with a voltage comparator. When the voltage is over the battery's maximum charge voltage, open the relay for a short but fixed time.

    perhaps I am getting your point.
    I have one circuit that show battery level with little LEDs. should I energize relay with LED showing battery full?
    will it work?

    Please forgive me for my English :(
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: help needed for charge controllers

    So you've found an oddball 72 Volt inverter for cheap and now need to supply 72 Volts for charging the battery bank from solar. You have a 48 Volt charge controller and a 24 Volt charge controller.

    If you divide the bank up into a 48 Volt section and a 24 Volt section for the controllers (but connected in series to provide 72 Volts for the inverter) it will work, to a degree. As I mentioned before the charging systems must be kept entirely isolated from each other on both positive and negative. But the two sections will be charged 'independently' as the two controllers will not work in concert; they won't see the battery bank as a whole and they won't have identical charging profiles.

    As such it will be important to keep an eye on the bank and make corrective charging measures (such as equalization) whenever the batteries become uneven in their state of charge.
  • BadarBadar Solar Expert Posts: 38
    Re: help needed for charge controllers

    Please correct me, if I am wrong: As per your suggestion I should do as following picture shows?

    Attachment not found.

    So you've found an oddball 72 Volt inverter for cheap and now need to supply 72 Volts for charging the battery bank from solar. You have a 48 Volt charge controller and a 24 Volt charge controller.

    If you divide the bank up into a 48 Volt section and a 24 Volt section for the controllers (but connected in series to provide 72 Volts for the inverter) it will work, to a degree. As I mentioned before the charging systems must be kept entirely isolated from each other on both positive and negative. But the two sections will be charged 'independently' as the two controllers will not work in concert; they won't see the battery bank as a whole and they won't have identical charging profiles.

    As such it will be important to keep an eye on the bank and make corrective charging measures (such as equalization) whenever the batteries become uneven in their state of charge.
  • mike95490mike95490 Solar Expert Posts: 9,261 ✭✭✭✭✭
    Re: help needed for charge controllers

    Looks like the photo will do that, but you will have to be SURE that there is no shared ground, through the panels, or internal controller grounding. And you will need to monitor the balance between segments, as the harvested wattage from 2 different sized arrays will never, ever, be the same.
    I'd say you will tire of it after a year, and spend the $ for the Midnight Classic that can do 72V.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: help needed for charge controllers

    in addition to the ground issue you will need to have dedicated pvs for each controller so that no pv sees more than 1 cc.
  • BadarBadar Solar Expert Posts: 38
    Re: help needed for charge controllers

    I would surely shift to midnight classic, but problem is that I am in Pakistan. Solar system is relstively new, most of solar installers are just stupid with no information and skills, and Alas!...... no Ecommerce culture here :(

    mike95490 wrote: »
    Looks like the photo will do that, but you will have to be SURE that there is no shared ground, through the panels, or internal controller grounding. And you will need to monitor the balance between segments, as the harvested wattage from 2 different sized arrays will never, ever, be the same.
    I'd say you will tire of it after a year, and spend the $ for the Midnight Classic that can do 72V.
  • BadarBadar Solar Expert Posts: 38
    Re: help needed for charge controllers
    niel wrote: »
    in addition to the ground issue you will need to have dedicated pvs for each controller so that no pv sees more than 1 cc.

    :blush:
    Yumyumyumyumyum..........
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: help needed for charge controllers
    Badar wrote: »
    :blush:
    Yumyumyumyumyum..........

    Niel is saying each charge controller must have its own panels. You cannot share either positive or negative connections on the inputs or outputs to the controllers; they must be completely isolated from one another.
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