Using a DC power charger to acharge a 12v Battery via a non MPPT solar controler

Atlas123
Atlas123 Registered Users Posts: 3
Hello,

I wasn't sure if to go to the newbie area but I found a similar question in this section of the forum, which is: http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/off-grid-solar-battery-systems/22364-using-a-16vdc-power-supply-with-a-pwm-charge-controller

[FONT=&quot]So I have a 12V portable battery (9ah) that I want to charge with solar or DC via a charge controller. The solar part I am good but I have seen a few comments that DC to charge controller could be an issue (at least for MPPT).

So, if on one side I have a non MPPT controller (Max 10a) and on the other I have a manually regulated universal charger with 4amps output max, specs as follows:[/FONT]

Output voltage no-load or with load: 12V 15V, 16V, 18V, 19V, 20V, 22V and 24V (-0.9/+0.8V)
Output current: 15V, 16V, 18V, 19V, 20V, 22V at 4.5A 90Watt, 22V, 24V at 4A 100Watt

So if I set-up the DC output at 15V, am I good without overheating/damaging something? Would I still need to add a resistor between the DC power and the charge controller?


[FONT=&quot]Thanks![/FONT]


Comments

  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    I do it regularly with a standard PWM charge controller and have had no issues to date. Obviously don't do it with an MPPT charge controller on a transformer type charger/power supply as the MPPT may overload the charger especially if the charger voltage is significantly higher than the battery voltage. Also make sure you put a big smoothing capacitor on the charge controller input as they don't like ripple currents...
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    It also depends on the type of DC output power supply you have... Some will current limit (i.e., 15 volts @ 4 amps or 12 volts @ 4 amps). Others will "hiccup" (try to take output to ~15 volts, see excessive current, shut down current output, try again).

    If your DC charger overheats or otherwise behaves badly, you may have to add a resistor to limit the output current to below 4 amps:
    • Voltage = Current * Resistance
    • R= V/I = (15 volts - 14.2 volts charging) / 4 amps = 0.2 Ohms
    • Power = I2R = (4 amps)2 * 0.2 Ohms = 3.2 Watt minimum power resistor rating
    And if your battery is significantly discharged (i.e., ~12.5 volts when charging), you may need a larger Ohm (and Wattage) rated resistor.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Atlas123
    Atlas123 Registered Users Posts: 3
    Hello all,
    Thank you for the info.

    So what I understand is:

    -From CALLD:
    An AC to DC converter may cause a ripple effect that the Charge controller may struggle with (which is not the case with Solar DC current, I guess the ripple with solar is less?)

    -From Bill:
    If the DC charger overheats that means there is an issue between the DC output amp and the Charge controller amps input and therefore may need a resistance to help dissipate the heat outside the DC charger.

    On CALLDs point: The AC to DC charger is designed for variable outputs to laptops (different voltage dependent on the laptop power requirements and swapping jacks) therefore I was assuming the DC current generated would be stable enough for a laptop (therefore also for a charge controller?). I read Inverters with modified Sine wave DC output could be risky for laptops (and pure sine too expensive). Of course I may be being too optimistic (or foolish :) ). Here is the detail about the charger that I am hoping has the necessary capacitors inbuilt for DC output:
    http://www.ebay.es/itm/251533900420?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
    I guess there is no way to check this without an oscilloscope or similar?

    On Bills point: Is this again something relevant to an AC to DC charger but not relevant if from a solar panel? I was hoping that with a 10amp charge controller that it could handle the amp variation from solar but also from the AC to DC charger.

    Just if interested, the setup I am planning is as such:
    -Solar panels (max 40W) or adjustable AC to DC charger 15V max 4 amps-->15a fuse--> 10a Charge controller --> Diode-->15a fuse-->12V Battery (9ah or 20ah)-->(maybe 15a fuse)-->Load
    -The load will have USB outputs and car plug output--> The same AC to DC charger has a car plug that can be used for DC to DC adjustable Voltage output depending on the laptop model.

    Thanks again!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    W OK, lots of questions... I take a stab at a few (others may have different answers):
    Atlas123 wrote: »
    -From CALLD:
    An AC to DC converter may cause a ripple effect that the Charge controller may struggle with (which is not the case with Solar DC current, I guess the ripple with solar is less?)

    There are lots of different types of power supplies... Some are simply a transformer and AC rectifier--And output lots of ripple current. If you have good size loads + ripple current on a Lead Acid Battery--It can cause the battery to get warm or even "micro cycle" (i.e., pull the operating voltage down below ~12.7 volts every 1/2 cycle--Then >12.7 volts on the other 1/2 cycle--discharging/charging ~60x a second).

    Also if using a PWM charge controller to keep the battery properly charged, these are "on/off" cycling too... Again can cause micro cycling in some cases (float voltage ~13.6 volts or so, generally the battery is kept above 12.7 volts and does not micro cycle).

    Adding some electrolytic capacitors at the battery can help reduce "ripple current" in the battery and keep it cooler too (that how I understood CALLD's answer).
    -From Bill:
    If the DC charger overheats that means there is an issue between the DC output amp and the Charge controller amps input and therefore may need a resistance to help dissipate the heat outside the DC charger.

    "It depends". If you have an electronic power supply, they generally will "protect" themselves against excessive current and overheating. How they do this can be very different between supply models and vendors. Some will keep at "4 amps" and simply let the output voltage drop--Not problem.

    However, others may try to regulate to 15.00 volts and if it takes more than 4 amps, they "shut down the output" for a short period of time (fraction of a second to a few seconds) and they try again. This type of supply may need a power resistor to prevent it operating in the "over current" output protection mode. Using a power resistor is a waste of energy--And is only used if there is no other method to fix the problem.

    A standard battery charger actually has two regulation modes. A maximum output current regulation mode (near dead battery, low voltage) that holds a maximum of "4 amps". And once the battery gets most of the way charged, it has a voltage regulation mode that holds 14.40 volts--And the battery charging current falls of naturally.
    On CALLDs point: The AC to DC charger is designed for variable outputs to laptops (different voltage dependent on the laptop power requirements and swapping jacks) therefore I was assuming the DC current generated would be stable enough for a laptop (therefore also for a charge controller?).

    Don't know... If you have a charger designed for a specific function (laptop charging) or is a "smart charger" that can configure itself for different applications--Most of the time, these are not designed for direct connection to a DC battery pack. Lead Acid batteries are pretty rugged--But improper charging can shave years off the life of a lead acid battery (over charging, boiling dry, under charging, etc.).
    I read Inverters with modified Sine wave DC output could be risky for laptops (and pure sine too expensive). Of course I may be being too optimistic (or foolish :) ).

    Another relatively complex subject. AC to DC switching power supplies typically had a full wave rectifier and a high voltage capacitor (~380 volts) to supply power do the switching output.

    If you fed these types of power supplies with MSW (modified square wave) Inverter power, the "sharp edges" of the MSW would cause excessive current to flow in the diode bridge and capacitors (ripple current)--And because of I2R heating... The high peak currents could overheat and damage the power supplies.

    If you had power supplies with small transformers--The poor "power factor" again can cause over heating of the step-down transformer (and circulating currents in the steel core).

    Newer/higher power switching power supplies have a "power factor corrected" front end which can work very nicely with MSW inverters--However, it can be difficult to tell which type power supply you have--So, I like to recommend TSW/PSW (True/Pure Sine Wave) inverters for people that need "reliable power" for their electronics/LED lighting/refrigerators... It is more expensive, but it can save you a bunch of money in the long term... Something like 80% of the AC appliances will work fine and 10% will have an early failure--Trying to figure out the difference is not easy.

    On the other hand, there are lots of MSW inverters out there running lots of loads/cabins out there--And the folks are reasonably happy with their installations.
    Here is the detail about the charger that I am hoping has the necessary capacitors inbuilt for DC output:
    http://www.ebay.es/itm/251533900420?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
    I guess there is no way to check this without an oscilloscope or similar?

    I see:
    Supports input voltage worldwide 100-260V

    Generally, this "wide range" of AC power (not 120/240 VAC with a "switch" but a broad input of 100-260+ VAC Input indicates that this is a PFC (power factor corrected) power supply. So, from my experience, this would be OK on a MSW power supply.
    On Bills point: Is this again something relevant to an AC to DC charger but not relevant if from a solar panel? I was hoping that with a 10amp charge controller that it could handle the amp variation from solar but also from the AC to DC charger.

    You are used to Lead Acid Batteries, DC power supplies, and utility power--Etc.... These are "voltage sources". The supply attempts to hold a fixed voltage no matter the current (until it is over loaded). Even an AC Utility outlet is a "voltage source" (just an AC voltage source).

    Solar panels are, more or less, "current sources". The solar panel will attempt to output a fixed current from ~zero volts to ~17.5 volts (for a 12 volt solar panel). No matter the voltage.

    From an engineering point of view, these are a "very different" type of power source and the rules governing how to use them are quite different. They are not simply "solar batteries" in the sense that most people understand.
    Just if interested, the setup I am planning is as such:
    -Solar panels (max 40W) or adjustable AC to DC charger 15V max 4 amps-->15a fuse--> 10a Charge controller --> Diode-->15a fuse-->12V Battery (9ah or 20ah)-->(maybe 15a fuse)-->Load
    -The load will have USB outputs and car plug output--> The same AC to DC charger has a car plug that can be used for DC to DC adjustable Voltage output depending on the laptop model.

    The details matter... I would be hesitant to use a universal laptop power supply as your DC power source--Unless it is really cheap and you don't mind experimenting/possibly ruining the supply.

    Also, the input voltage to the Prostar.... 15 volts is about the very minimum that would work with a small 12 volt battery (that probably needs around 14.2 volts to charge). And Lead Acid batteries can require anywhere from 14 to 15 volts to properly/quickly recharge... It depends on the battery type (flooded cell, AGM, GEL, SLA/VRLA), temperature, etc. What works on a warm battery may not if the battery is near freezing or below. And holding 14.2 volts for days on end can overcharge and damage the battery too.

    Connecting a bunch of different devices together may not work out well.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Atlas123 wrote: »
    Just if interested, the setup I am planning is as such:
    -Solar panels (max 40W) or adjustable AC to DC charger 15V max 4 amps-->15a fuse--> 10a Charge controller --> Diode-->15a fuse-->12V Battery (9ah or 20ah)-->(maybe 15a fuse)-->Load

    There's not much left to say after Bill's reply except: You don't need that diode. I've never heard of a charge controller that needs a diode. A diode will cause voltage drop and will interfere with the ability of most charge controllers to regulate the charge.

    Also, the fuse between the battery and the load is not 'maybe', it is mandatory. A fuse between the solar panel and the charge controller is optional, but a switch or circuit breaker is a great convenience... most charge controllers must be connected to a battery BEFORE being connected to the solar panel.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Jake48
    Jake48 Registered Users Posts: 11
    or you can possible try to somehow, (magnets, specific magnet cables, or make your own wind turbine) make your own power supply. note: save the ends of the appliance good for something still right?.
  • Atlas123
    Atlas123 Registered Users Posts: 3
    [FONT=&quot]Thank you very much for the responses and specially to Bill for the detailed information and the time spent on it :).

    I will look into having 2 power entry points:
    - one for solar (direct to charge controller)
    - and the other for the AC to DC charger, for this second one I will look into adding something like this to reduce the ripple:
    http://www.ebay.com/itm/DC-CC-280W-Step-Down-Buck-Converter-7-40V-To-1-2-35V-Power-module-/321576507977

    It should help with ripple, probably also dissipating heat and can further help with regulating the voltage into the Charge controller (I think there was also something about it making nice cocktails if the current was right...)

    BTW it all goes into a box as a portable generator. In principle I would only have 1 load being used: or USB devices or a laptop (an old one for the time being just in case). The idea is to have this charge with a total of 10W from solar from home or outdoors (only as top-up, best case it will charge 4 amps in a day I think), but if I need to charge faster before going out then I have the option to use the mains.

    I still have to think abut the process to maintain the life of the battery but the DC charger for the 12V battery is a punctual thing (not plugging always the battery on AC to DC). The part that would be plugged most of the time would be the 10W solar.

    vtmaps: On the Diode question probably the placement is not accurate and it should just be between the solar panel and the charge controller. (to avoid discharge during the night etc) I had though that the charge controller could also drain the battery although I am hoping that the switch would turn off the charge controller and avoid discharge, I will test when I have all the parts. Thanks also on the fuses part.

    Jake48: At the moment building this "mostly" solar portable battery to get acquainted with some of the basics of solar & electricity, then thinking about building a small array for specific house needs (office PC etc set-up). Other projects to look into before wind turbines (not sure if even legal where I am due to regulation, national or local). So probably enough hobby work time for a few decades :)

    Thank you all, I will try to give an update that hopefully does not involve burning stuff out...

    [/FONT]





  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Atlas123 wrote: »
    vtmaps: On the Diode question probably the placement is not accurate and it should just be between the solar panel and the charge controller. (to avoid discharge during the night etc) I had though that the charge controller could also drain the battery although I am hoping that the switch would turn off the charge controller and avoid discharge,

    The diode is not needed there (between the panels and the controller) either.

    You are correct that most charge controllers will have a slight draw at night to power their electronics. If you wish to power down the controller, you must first disconnect the panels from the controller, and then disconnect the battery from the controller.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i