Voltage reducers

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  • Lachie
    Junior Member
    • Aug 2018
    • 5
    #1

    Voltage reducers

    Hey gang. I recently acquired a second 170W hand solar panel that used to be used on a house. I am hoping to be able to use it on my van to charge me auxiliary battery. I currently run a ctek d250s in the van which has a solar controller built in so I am hoping to be able to use that. Problem is the panel is 36V and the max input for the ctek is 23v. So in my research I have found a few voltage reducers on eBay that look like they will do the job of reducing the voltage from 36v to 12v but I am unsure of how many amps it needs to be?? I found one that I will attach a photo of that reduces to 12v 15A 180W but I'm not sure if 15A is way too much. Especially considering the panel is only 5amp to begin with... The ones I have found that reduce to 12v 5A only say 60W which coming from a 170 watt panel kind of defeats the purpose . I'll attach some photos below.
    thank you in advance for any help.
    Attached Files
    Tags: None
    • PNPmacnab
      Solar Fanatic
      • Nov 2016
      • 425
      #2
      Depends on what you want to do with that 12V. Those modules put out almost precisely 12V. Fine to run 12V things, but you can't charge a battery which can need almost 15V. I use a number of 180W converters like that which come in a rectangular box and only cost $5. Don't expect to get even half the amps specified.

        Comment

        • jflorey2
          Solar Fanatic
          • Aug 2015
          • 2331
          #3
          Originally posted by Lachie
          Problem is the panel is 36V and the max input for the ctek is 23v. So in my research I have found a few voltage reducers on eBay that look like they will do the job of reducing the voltage from 36v to 12v but I am unsure of how many amps it needs to be??
          You need an MPPT charge controller. The DC/DC you show won't work because the panel's impedance will be too high. They are available for ~$100.

          To figure out current:

          Take your solar panel (170 watts.) That means your realistic power output is (170*80%) = 136 watts. Now divide by voltage (13.8 volts) Result - 9.8 amps.

            Comment

            • Lachie
              Junior Member
              • Aug 2018
              • 5
              #4
              Originally posted by jflorey2
              You need an MPPT charge controller. The DC/DC you show won't work because the panel's impedance will be too high. They are available for ~$100.
              I'm not sure I get what you mean. Are you saying I can't use the ctek at all? Or are you saying I need to use another charge controller as well as the ctek?? I'm confused. As far as I can tell the panel is currently to big for the ctek charger but if I can reduce the voltage to a more something like 15V then it should work??

                Comment

                • Mike90250
                  Moderator
                  • May 2009
                  • 16020
                  #5
                  I'll say you cannot effectively use a 'voltage reducer' or any ordinary DC-DC converter to reduce PV array voltage to acceptable limits for battery charging.

                  Just get a decent MPPT Charge Controller and let it do the work properly. Ordinary DC-DC converters cannot manage the varied current output from a PV panel, and will collapse the voltage and just shut down.
                  Powerfab top of pole PV mount (2) | 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

                    Comment

                    • Lachie
                      Junior Member
                      • Aug 2018
                      • 5
                      #6
                      Originally posted by Mike90250
                      Just get a decent MPPT Charge Controller and let it do the work properly.
                      could I not just use a PWM like the one attached? As the main reason I got the second hand panel as apposed to buying new is to save some coin. Are these PWM modules still going to do a decent job?? I'll attach a link too for more info.
                      jaycar.com.au
                      https://www.jaycar.com.au/12-24v-10a-solar-charge-controller-with-usb/p/MP3750
                      Attached Files

                        Comment

                        • Mike90250
                          Moderator
                          • May 2009
                          • 16020
                          #7
                          Originally posted by Lachie

                          could I not just use a PWM like the one attached? As the main reason I got the second hand panel as apposed to buying new is to save some coin. Are these PWM modules still going to do a decent job?? I'll attach a link too for more info.
                          https://www.jaycar.com.au/12-24v-10a...h-usb/p/MP3750
                          No.

                          panel puts 170W @ 36V. That works out to 4.7A

                          A PWM module will give you 4.7A @ 14V which is only 66w from your panel

                          A MPPT controller will give you a genuine down-conversion and you will get about 165 watts with just a few % loss.
                          The morningstar 15A sunsaver MPPT
                          SunSaver MPPT - Morningstar Corporation
                          https://www.morningstarcorp.com/products/sunsaver-mppt/
                          SunSaver MPPT, Morningstar Corporation, Solar, Charge Controller, 15 Amp, Maximum Power Point Tracking

                          will give you 14V at about 11.7A
                          Powerfab top of pole PV mount (2) | 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

                            Comment

                            • jflorey2
                              Solar Fanatic
                              • Aug 2015
                              • 2331
                              #8
                              See below for longer answer.
                              Last edited by jflorey2; 09-04-2018, 05:53 PM. Reason: Updated answer below

                                Comment

                                • jflorey2
                                  Solar Fanatic
                                  • Aug 2015
                                  • 2331
                                  #9
                                  Originally posted by Lachie
                                  I'm not sure I get what you mean. Are you saying I can't use the ctek at all?
                                  You can use the CTEK in its original application. You can't use it to get much power from the panel.
                                  Or are you saying I need to use another charge controller as well as the ctek??
                                  Well, you could connect an MPPT controller to the battery in parallel with the CTEK. Then the CTEK wouldn't control solar charging but it would do all its usual stuff.
                                  could I not just use a PWM like the one attached?
                                  Sure. You will lose 60-70% of the panel's energy, but it will work (as long as the PWM controller has a high enough standoff voltage, and most PWM controllers go to at least 50 volts.) You CANNOT use a cheap DC/DC to get more power. That's what a PWM is for.
                                  As the main reason I got the second hand panel as apposed to buying new is to save some coin.
                                  Yep. You bought some cheap stuff and then found out it's not as good as you hoped. In the end you would have saved money by buying appropriate equipment.
                                  Last edited by jflorey2; 09-04-2018, 05:57 PM.

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