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DC-DC buck converter to reduce voltage to loads. was : I'll share this with you

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  • DC-DC buck converter to reduce voltage to loads. was : I'll share this with you

    I'll share this with you maybe someone will find this useful If you use a 24VDC to 12vdc converter you will save 15% of your charge when using it because it lowers the voltage of a charged battery 14.5VDC to 12.3VDC saving energy. Some voltage controller will not work this way I just returned and got a different brand. They are about 20 dollars for a 40 amp/480 watt converter. Doing this save energy (15%) , lowers temp of your devices and reduces stress on the system.

    I hope someone finds this useful.
    Last edited by Mike90250; 12-25-2020, 03:29 PM.

  • #2
    Don't get how this saves money or helps. I think you're selling a PWM controller or suggesting to use a buck converter for a charge controller.

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    • #3
      No, I 'm using a buck converter off the battery bank to lower the full charge of battery bank from around 14VDC to 12.3VDC saving 14 - 12.3 = 1.7 /14 = 8.235%. Also running @ 12.3VDC is cooler(makes less heat) and less stress on the devices. This mod isn't for ever body but the system is going in my van and I'm doing ever thing I can to reduce heat.

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      • #4
        I know you have your reasons and don't want to come across wrong, just trying to understand. Maybe you've got other than FLA.

        Why are you trying to save heat? I thought heat would be a problem with charging my battery 440 ah FLA bank at 45 amps, but I don't see a temp increase when the temps outside are around 70 F. Maybe in the summer, but I have not been there yet. I have the batteries enclosed in a plastic box with a thermometer on them. I've seen the batteries get 4 degrees warmer than air temp.

        What does your battery bank manufacturer spec sheet say to charge the batteries at?

        Also, for my FLA Batteries, 12.3 volts = 65% SOC. I must be missing something on this. I would think chink charging the battery to 100%, 12.74 volts, and then being sure to deplete it as little as possible, to say 80%, 12.50 volts, would get me twice as many discharges as compared to going down to 50% every cycle. At least that's what my spec sheet says.

        There's also the 13.6 to 13.8 volts needed to put on a battery so that amps out = amps in. That way, when a load gets turned on, the amps come from the alternator not the battery. First heard about this point when fixing cars. Saw this demonstrated on a YouTube video where a clamp meter was placed at the battery, the load, and the alternator to measure where the amps were coming from. This also lines up with my float voltage from my battery's spec sheet.

        MPPT charge controllers are "supposed" to be more efficient than PWM controllers in most circumstances, 15% to 25%, and buck converters are not a good choice. At least that's conventional wisdom. I'm planning a second build now, where I will be confined by space, and if you're on to something, I may incorporate this.

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        • #5
          We may be over-thinking his idea. I think he is simply using a switching regulator to slightly reduce the voltage (14.5V to 12.3V) so that the lights draw less power. This won't do any good for electronic loads that pull constant power or a refrigerator that has temperature control, but would save power in incandescent lamps.

          Of course, when an incandescent lamp is run at a lower voltage, it draws less power and puts out less light. More importantly, incandescent bulbs are less efficient at lower voltages, so with old-fashioned 12V bulbs, you need more bulbs and more watts at lower voltage to get the same amount of light. The bulbs will also last longer.
          7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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          • #6
            Voltage controller don't effect the battery bank voltage because I'm running the voltage controller off the battery bank. The heat I'm concerned about isn't the battery heat it is inside the van heat I'm concerned with. Power is heat the less used the less heat you have its direct relation one to the to the other. Lower power means less charging cycles. I have tested this with the bank of LED lights I will install they are just as bright @ 12vdc as 14.3VDC and they measured 10% less power draw. Voltage controllers are 98% efficient converting from 27VDC to 12.3VDC I assume the efficiency is much better at 14.3VDC to 12.3VDC. I'm using the voltage converter just on the DC bus nothing to do with the AC. Thank You for the info you given ideas to think about.

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            • #7
              Large LEDs are used extensively in the indoor gardening industry. This method of running them at 80% or less capacity is often used to save power and extend life. Most manufacturers like Cree publish extensive documentation. I believe current limiting is used more often because of the minimum voltage needed. Nominal voltage of an LED IS 3.5 Volts so there may already be some conversion going on in your fixture or bulb.
              Last edited by Ampster; 12-24-2020, 02:20 PM.
              9 kW solar. Driving EVs since 2012

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              • #8
                Hello,

                When I get the system up and running I'll test it by turning on all the 12VDC devices and measure the watts and amps. Then I'll bypass the two main solid state relays which will bypass the two voltage converters and then I'll share the results. Then I'll get a good idea of its performance. My guess right now is 8%. I have been bypassing the power supply on some devices that run on ACV and most of the time internally they power down to a 12VDC so their more efficient because they don't have to convert from VAC to VDC. Thanks

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                • #9
                  Volt and Amp measurements will give you more usefull data.
                  9 kW solar. Driving EVs since 2012

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                  • #10
                    The voltage controllers keeps the voltage fixed 12.3 all the time except for a major screwup. That's one of nice things about them its always 12.3 regardless of the load. If load is much over 40 amps it may very but it should always stay at 12.3VDC all the time as long as load is under 40 amps. Its a voltage device. Thanks
                    Last edited by Rover; 12-27-2020, 02:21 AM.

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                    • #11
                      Originally posted by Rover View Post
                      I'll share this with you maybe someone will find this useful .....
                      I found it much more useful to update your post header with something more accurate.
                      Mod

                      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

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                      • #12
                        Originally posted by Rover View Post
                        I'll share this with you maybe someone will find this useful If you use a 24VDC to 12vdc converter you will save 15% of your charge when using it because it lowers the voltage of a charged battery 14.5VDC to 12.3VDC saving energy. .
                        How many years did it take you to become that stupid?

                        1. You lose energy down or up converting voltage.
                        2. Unless you have a purely resistive load like an incandescent light bulb, today loads are constant power consumption. Lower voltage means higher current. Higher current means higher wiring losses.
                        Last edited by Sunking; 12-26-2020, 09:47 PM.
                        MSEE, PE

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                        • #13
                          Manufacturer claims this device is 98% efficient at stepping down voltage from 27VDC to 12.3VDC. I'm assuming they are a lot more efficient converting from 14VDC to 12.3VDC my guess is they are greater than 99.7%. I'm wiring a van with a front and back 12.3 volt panels feed by 4 feet 2/0 cable the longest run from the 12.3 VDC boxes is 6 feet I'm not concerned about losses because their will not be any that anyone beside you would be concerned about. The two 12VDC boxes are fused with 30 amp mains.
                          Last edited by Rover; 12-27-2020, 02:43 AM.

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                          • #14
                            Originally posted by Rover View Post
                            Manufacturer claims this device is 98% efficient at stepping down voltage from 27VDC to 12.3VDC. I'm assuming they are a lot more efficient converting from 14VDC to 12.3VDC my guess is they are greater than 99.7%. I'm wiring a van with a front and back 12.3 volt panels feed by 4 feet 2/0 cable the longest run from the 12.3 VDC boxes is 6 feet I'm not concerned about losses because their will not be any that anyone beside you would be concerned about. The two 12VDC boxes are fused with 30 amp mains.
                            And I can claim magical thinking. Seriously, the mfg will have power curve charts. Check them. My guess is they jibber jab talk using the highest point of their curve (all of them do, up to 98% of them) and any other point on the curve is going to be less.
                            My concern is you have been fed a line of BS from some vendor, and because you want something to work that way, you are taking it hook line and sinker.

                            What does the mfg's published chart show ? It's OK to post link to Mfg data sheet - your vendor should be able to give you that. Without expensive gear, an individual is unlikely to be able to measure the difference between 90 and 98% with any confidence.

                            Another factor is where is all this power coming from ? You are talking about "lots of heat" and if saving 4 or 5% of power is going to make a great reduction, how long are the batteries going to last ?

                            Here's a couple snippets from a 300w class DC -DC from a major maker, just so you can see what your vendor is supposed to show you. In plain english, they say 96% peak, a couple mid range #'s and an average under different loads 80%. A good data sheet is 20 pages of charts, tables and graphs, otherwise, you are getting smoke blown at ya.
                            I found no reputable DC-DC in the 27 - 12V range without getting into >$400 parts. Ignore the voltages listed, read the efficiency %, - power is power, and low voltages are higher losses !


                            VicorEffTable.jpg

                            VicorEffGraph.jpg

                            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


                            • #15
                              I'm sorry I should say to the group that this device comes in 36 and 48 VDC models also if you have the higher voltage system like 48 VDC use a 48 to 12 VDC or what ever your needs are but that I choose a 12 VDC system because the devices in that voltage range are easy to find cheap and I'm proud to say I'm cheap.
                              Last edited by Rover; 12-27-2020, 06:23 AM.

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