Using a 16VDC power supply with a PWM charge controller

soylentgreen
soylentgreen Solar Expert Posts: 111 ✭✭
I have a camper van with an 85W solar panel and SunSaver Duo charge controller, which nicely will charge both the house (RV) battery and starting battery independently.

Unfortunately, the van is mostly parked in a garage, and although the van has a built-in charger, it is shot.

So, in the name of Science, about a year ago, I purchased a cheap adjustable voltage DC power supply, set it to 16VDC and plugged it in lieu of the solar panel. It worked great (the SunSaver charge controller thought it was getting solar DC, would charge up both batteries, etc).

However, the power supply ran very hot, and after about 20 uses, it died.

My guess is, although solar panels don't care if they are being chopped with a PWM waveform, perhaps DC power supplies do?

Now, I'm thinking I can either
(A) buy a purpose-built charger that has 2 battery charging capability
(B) buy a high-quality 16VDC power supply

In the name of Science, I like option (B) although I can see many reasons to go with (A).

Any thoughts about whether my failing was "buying a cheap DC power supply" vs. "hooking any DC power supply to a PWM charge controller"? If I go with option (B), would a big honking capacitor in-line perhaps help the power supply not be killed by the PWM chop?

Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    The big problem is that a PWM controller does nothing to regulate the peak current drawn from the source.
    If the source is a PV array, that current will be limited by the available sunlight and no damage will occur.
    If, on the other hand, you have a "stiff" power source like a regulated power supply, the current will go far above the rated output.
    Even if the power supply has fuses or other protection, the problem, as you suspected, is that the peak current can damage the supply even if the average current is within limits.

    You might be able to salvage the situation by putting a power resistor in series with the 16V supply output to limit the peak current.

    If you use an MPPT CC instead, the problem is even worse in some ways: The CC will keep trying to draw more and more current until it gets the maximum available power (up to the limit of what it can supply to the batteries). It will deliberately overload the power supply and kill it at part of that operating mode.

    A capacitor will do you no good except perhaps to kill the CC instead of the power supply.
    SMA SB 3000, old BP panels.
  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    Interesting, thanks.

    My thought was that perhaps some sort of transient spikes from the PWM chop was hurting the DC power supply (much as, I've read, you can easily fry your 12V alternator if you disconnect it while at full load).

    If I am understanding, it sounds like you are saying the problem is different: that while the PWM is in the ON state, the power supply is basically delivering over it's rated wattage. This sort of makes sense, although on the other hand the PWM is not dead-shorting it, rather it's being connected to a 260AH 12V battery which is sitting at around 12V. Is 16V into that receptacle really enough to cause a power supply overload?

    Any thoughts about whether a better power supply would be happy about this? I quite expect cheap junk power supplies to die while mistreated, I guess I'm just not sure what "mistreated" is in this context...
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    I suspect you would be best off with option C) buy two standard battery chargers. But you can buy current limited power supplies that will never deliver more current than they can handle.

    I am available for custom hardware/firmware development

  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    Re: Using a 16VDC power supply with a PWM charge controller
    jonr wrote: »
    I suspect you would be best off with option C) buy two standard battery chargers. But you can buy current limited power supplies that will never deliver more current than they can handle.

    I'm not sure that adding two more charging circuits to my van which already has 3 is the way to go, but I am intrigued by the idea of a power supply that won't kill itself.
    Here's one I'm thinking of: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2102211_-1

    It's from the well-regarded "Mean Well" brand. Have you hear their advertising jingle? "When you hear "Mean Well", you know we are really very sorry your house burnt down!"
  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    A new question: Why 16V? The PWM charge controller has a peak of 14.8V for "boost" (equalization) voltage. I figured a diode was probably involved, so I added 0.7V and rounded up. It seems as if matching the DC power supply voltage to the charging voltage would be good - reduce the PWM chop. Anyone know how these PWMs actually work? Is there a voltage loss in the "ON" state?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a 16VDC power supply with a PWM charge controller

    In itself, 16 volts is fine.

    The problem is the AC to DC regulator... Some are designed to limit output current, and others will output as much current as they can until they overheat/fold back (like a short circuit).

    Some, can through a "crowbar" across the output... Of course, "crowbaring" the output when connected to a good size battery is not going to give happy results (crowbaring into a computer/other load, it protects the loads from damage from a run away power supply).

    Battery charging systems are designed (usually) to output full current and no more (current regulation) until the battery reaches a set point (say 14.5 volts), then it goes into voltage regulation.

    Placing a PWM controller between the "wrong type" DC supply and the battery bank--You will probably have problems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    And in case all of the above isnt clear enough placing a 16V power supply across a 12v battery pretty much amounts to 4v placed across a dead short. Current will flow! You want either something with in built current limiting, ( not foldback as noted above), OR add a beefy power resister to limit the current. Youll need to experiment / math the exact value of resistance required.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller
    Now, I'm thinking I can either
    (A) buy a purpose-built charger that has 2 battery charging capability
    (B) buy a high-quality 16VDC power supply

    You can have your cake and eat it too with these:
    http://www.samlexamerica.com/products/ProductsList.aspx?cid=S14

    You can choose power supply, or battery charger that can handle multiple banks by flipping some switches.

    When you use a power supply not specifically designed to charge batteries, the load they see appears almost like a dead short. If they don't throw crowbars or other protection circuitry, they run very hot into a near-short.

    A pwm CC doesn't really do much until it reaches the terminal voltage limit you have set. Thus in the bulk cycle, it is as if you have connected the panels directly to the battery. Once the battery terminal voltage rises during charge, when it gets close to the voltage setting, it starts to merely switch the connection on and off really fast, the off time being the "width" of pwm. The end effect is that it is not really clamping the voltage per se, but due to the speed of the switching, the net result is a voltage regulation.

    Most of the damage to the cheap power supply is done in the bulk stage, so the chopping effect of pwm actually helped the supply live just a little bit longer than a linear regulator would.
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    > the chopping effect of pwm

    Some battery charging specifications refer to a low limit on allowed ripple. Doesn't a PWM controller exceed this? Maybe not so much in this case (only 16V and will probably have a reasonable current limit), but in cases where the supply voltage and current are higher.

    I am available for custom hardware/firmware development

  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    I can tell you that the IOTA power converters work just fine with the plug in the Jack on a Xantrex C-35 without issue, You can crank voltage up to 15.5V / 31 V and and set the Bulk / Absorb & Float in the controller and EQ from the CC. They are constant voltage, not constant current. It's a expensive way to have a nice battery charger though and the C-35 only Absorbs for a hour, but you can control the voltage.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    you're kind of going around in circles just to be able to use a pwm controller. just replace the stuff that went bad and use the cc for solar.
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Using a 16VDC power supply with a PWM charge controller
    jonr wrote: »
    > the chopping effect of pwm

    Some battery charging specifications refer to a low limit on allowed ripple. Doesn't a PWM controller exceed this?

    Nope. If it did, then every single charge controller manufacturer would be out of business. Note that even mppt-controllers use pwm in absorb to regulate voltage. Of course it ALSO has maximum power point tracking, which a standard low cost pwm type doesn't. Different technology, but the point is that pwm is there as well.

    If that is a really big concern for whatever reason, then one can fall back on hysteresis-charging, which is not efficient. That would just be allowing the battery to ping-pong between a low and high voltage window. Old / cheap solar controllers do this. In a way, you could consider this pwm, but the duty cycle is so low that it is not really in the same category. :)
  • Sun Dog
    Sun Dog Solar Expert Posts: 115 ✭✭
    Re: Using a 16VDC power supply with a PWM charge controller

    I have also been looking into using a power supply as a battery charger (in my case, for an odd size voltage). The most economical solution I have come up with is the EX line from Volteq/Mastech. This one looks like a good match for you. Set the voltage at 14.8V and the amps at 20A and away you go. Of course you will have to monitor it and if you want to be able to run an equalization voltage you will need a model with a higher voltage capacity. http://www.mastechpowersupply.com/dc-power-supply/switching-power-supply/volteq-power-supply-hy1520ex-15v-20a-over-voltage-over-current-protection/prod_77.html

    With something like this you could charge pretty much any battery under 12V and up to ~400Ah (based on a charging rate of C/20)
  • sfpcservice
    sfpcservice Registered Users Posts: 1
    http://youtu.be/QeXHlhIr1hA

    I actually did this with a morningstar Mppt controller. I made a video showing my setup.
  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    edited November 2020 #16
    To follow up on an old thread:  I ended up purchasing the MeanWell power supply https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2102211_-1  
    Set it to about 15.0V, and plugged it into the input of the SunSaver Duo, and plugged the MeanWell into the van's shore power input.

    It's been functionally working great for years, and is super convenient:
    1. When I get home, just plug the van into shore power.  That's it.  No switches to flip.
    2. All charging/monitoring is handled via the SunSaver Duo + Remote monitor.  I don't have to worry about multiple systems.
    So I like it.

    However, I recently did some upgrades:
    1. Changed house battery from flooded lead acid to LiFePO4.
    2. Added interior strip LED lighting controlled by a a PWM dimmer
    3. Upgraded to a pure sine wave inverter.
    After the upgrades, I notice some weird behavior when charging:
    1. the LED lights have a noticeable flicker.
    2. the inverter, when powering a heavy load (600 watts) seems to have brief a periodic dip, (you can hear the fan slow down for a blip).  The dip happens almost exactly once per second.  The load is a pure resisitve load (electric water heating element) so it should not be doing anything weird.

    Things I've tried:
    • I built a home-made RC (resisitor / capacitor) low pass filter with a 100Hz cutoff frequency, and plugging the LED lights into this does help, but does not eliminate the flicker.  
    • I tried two different brands of LED dimmers, and both show the issue.  One uses 100Hz PWM, the other uses 180Hz PWM.   The 180HZ model is better.
    • I tried adjusting the Voltage of the power supply (from 13.7 up to 18.0).  At the lower voltage, the charging current drops closer to zero, and at the higher voltage the current gets high enough to hit the limiters (the power supply claims a 22A limit, and SunSaver duo claims 25A).   I've seen the SunSaver Duo go into "failure" mode around 25A : it disconnects the charger, waits a bit, then tries again.  I have not seen the Power supply clip to 22A.   Regardless of the voltage, I still see the flicker on LED and surge on inverter, though it is worse as the voltage and amps go higher.
    • Turned off the charger, and moved the van into the sun.  On solar panel, I can still see the flicker (but not the 1 per second surge).  The LED flicker is much more sublte, but still there. My solar panel is only delivering about 3 amps at the moment.
    • Tried fliping the "regulation method" switch on the SunSaver Duo, which is supposed to change it between 300Hz PWM or "slow switching" (10Hz PWM).  I expected this to change things but seemed to have no effect, which doesn't seem right. 
    So I think I have two issues:
    1. PWM charge controller inhernetly gives dirty power, and using a PWM LED dimmer is sensitive to this dirty power - worsened by the fact that the frequency ranges of the two PWMs are close (300Hz vs 180Hz).
    2. Some other issue causing the "one per second" dip/surge.  I almost wonder if there is some complex interaction?   The battery is a BattleBorn 100AH 12v which has a BMS, which is supposed to tolerate 100A for 30 seconds, so in theory it shouldn't be doing anything. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    First your charging setup... 13.7 to 18.0 volts? I don't understand.

    The charging voltage for Battle Born is:
    https://battlebornbatteries.com/product/12v-lifepo4-deep-cycle-battery/
    • Charging voltage: 14.2 – 14.6 V
    • Float voltage: 13.6 V or lower
    What is your battery bus voltage when charging? What is the voltage when the LEDs are flickering?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    The voltage on the battery side is fine: the SunSaver Duo aims for 14.1 bulk and 13.7 float.  

    What I’m adjusting is the voltage on the DC power supply which is simulating a solar panel.    

    My theory is that if the supply voltage matches the target voltage then the charge controller will stop doing PWM modulation, giving me less noise or ripple. 

    I just had an idea. The “Duo” part of SunSaver Duo means it supports charging two batteries: a house battery and a starting battery, and is currently set to give 90% of the charge to the house battery and 10% of the charge to the starting battery.  

    This 10:90 ratio is awfully similar to the once per second voltage dip that I’m seeing. I had assumed the charge controller would charge both batteries at the same time. Maybe it alternates between the two batteries, once per second?

    I have an oscilloscope, I need to see if I can get some readings on what’s actually going on and will report back.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited November 2020 #19
    Do not put a power supply to the input of a charge controller.   A solar panel is a CURRENT SOURCE device and a charge controller is designed to work with that.
      A power supply is a VOLTAGE SOURCE and will not work well.

    So you do what the pros do, you decide what the float voltage for your batteries is  and you connect your preset power supply to the batteries.
    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 ,

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    You could always refer to Morningstar, this is from their website's FAQ section.

    Using a DC power supply as a PV panel substitute?

    Morningstar PWM controllers are not designed to properly process input from a DC power supply. This type of input is not recommended and is connected at the user’s risk. DC power supplies have considerably more output capacitance than PV panels and connecting a DC power supply to a Morningstar PWM controller may cause excessive heating and premature failure.

    MPPT controllers can be used for this application with no issue

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    > MPPT controllers can be used for this application with no issue
    Beware - this is a Morningstar document.  It's not applicable to other brands.
    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 ,

  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    Great info, thanks.   I was actually wondering if putting more capacitance on the DC power supply output would help, but it sounds like that's the exact opposite of what's needed.

    1. I've seen a few comments that some MPPT controllers may still use PWM in certain situations.  Is that true?  If so, seems like the problem of dirty power might still be an issue.  Is there any way to tell which MPPT controllers do that?

    2. Searching around for "Flickering LED RV" I've seen a number of other people having similar problems, even if they are using the proper charge controllers and not trying to do something weird like I am.   It sounds like one solution is to get a small DC-DC converter and use that for sensitive loads such as LED dimmers.

    3. Does anyone make a dual-battery MPPT charge controller?   


  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    AFIK, ALL MPPT controllers, fall back to PWM when the additional energy from downconversion is not required.

    Flickering LED's are from a cheap PWM with very low frequency ( under 100hz) modulation. or using Low RF noise  mode

    https://www.morningstarcorp.com/products/sunsaver-duo/   PWM though.

    Lousy LED driver design can also cause flicker, using better LEDs would help.



    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 ,

  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    edited April 2021 #24
    I found a pretty decent solution to my flickering LED problem:   https://www.amazon.com/gp/product/B07WFMG11F   which is a DC-DC buck/Boost voltage converter.  I picked the version that outputs 13.8VDC at up to 10 amps.    Now, my dimmable LEDs are bright and completely flicker-free.  Things which used to cause flicker (charging via PWM charge controller, or turning on/off a water pump) no longer cause any visible change to my LED lighting.  

    I still plan to move to a MPPT charge controller, but for the moment the biggest headache is fixed.