Best way to convert voltage?

backroadbackroad Solar Expert Posts: 185 ✭✭✭✭✭
I'm now at the point where I'm needing to install my 24 volt water pump and my 12 volt coolers(could be upgraded to 24v).

Am I better off to convert from 120v to 24 and/or 12v or should I be considering a power converter from 48v to 24v.

I used to just pull 12v for my coolers from 2 of the batteries in my old 24v battery bank. I PROMISE THAT I WILL NOT DO THAT AGAIN....:):):)

THANX....

Comments

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Best way to convert voltage?

    Power Converter 24 to 12 or Look at using the Morning Star 15 Amp MPPT charge controller and a small 12 volt buffer battery (assuming 15 amps of 12 volt is enough).

    -Bill

    If you have need for 120 VAC anyway--a good TSW inverter is probably the most convenient.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Best way to convert voltage?

    The definition of 'best' may depend on your personnal opinion.

    The best from a pure power conversion would be a DC-DC switching converter like:

    http://www.rpelectronics.com/Default.asp?Main=/English/OnlineCat.asp?Menu=/English/Content/Categories/CatM_68.asp%26Detail=/English/Content/Items/SDC23.asp

    At $140 it may not be viewed as 'best' solution.

    If your 12v coolers are Peltier junction coolers you are already throwing away a lot of power for cooling.

    The lowest cost solution would likely be a 120vac to 13.8vdc adaptor if you already have an inverter.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭✭✭✭✭
    Re: Best way to convert voltage?

    In addition to "personal opinion", "best" also depends on the amount of power that's required.

    A switch mode power supply, such as you might find in a DC-to-DC converter is going to be very efficient, but also very expensive. They are available in a wide range of sizes -- but cost-per-amp can be excessive for small loads.

    An MPPT charge controller and buffer battery might be cost-effective compared to a DC-to-DC converter. For an intermittent load you could use a smaller MPPT controller than the load, allowing the battery to charge and discharge during cooler cycles. I'd compared the cost of that route with the first option I listed, then decide based on cost.

    For low power applications, a 120VAC wall-wart type power supply would be cheap, but inefficient. On the other hand, if the load isn't that great, lousy efficiency isn't as much a problem as with a larger load.

    If you post more info, you'll get more opinions!
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Best way to convert voltage?
    tallgirl wrote: »
    If you post more info, you'll get more opinions!
    We have lots of issues around here--However, lack of opinions around is not one of them. :p

    -Bill ;):D
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • backroadbackroad Solar Expert Posts: 185 ✭✭✭✭✭
    Re: Best way to convert voltage?

    Funny thing... Me thinks that's why I asked the question. Bring on the opinions please.
    My battery bank is 48v.............so....48v > 24v
    BTW....The water pump says on the label that it pulls no more than 6 amps at 24 volts.

    ....The 24v coolers say they pull about 130 watts each and I had planned on running two.

    Check my if I'm wrong, but that seems to need 10-15 amps for all 3?
  • halfcrazyhalfcrazy Solar Expert Posts: 717 ✭✭✭
    Re: Best way to convert voltage?

    could you run the 2 coolers in series thus using 48vdc?
  • backroadbackroad Solar Expert Posts: 185 ✭✭✭✭✭
    Re: Best way to convert voltage?

    I don't think so. That would still be 48v to 24. Actually my current coolers are still 12v, but am planning on buying the others, which could be bought in 48v also.
  • backroadbackroad Solar Expert Posts: 185 ✭✭✭✭✭
    Re: Best way to convert voltage?

    From what I'm finding so far is that DC>DC and AC>DC converters are really in the same ballpark cost wise. AC>DC produces 25 amps for about $250. DC>DC produces about 15 amps for $235.
  • mike95490mike95490 Solar Expert Posts: 7,286 ✭✭✭✭
    Re: Best way to convert voltage?
    RCinFLA wrote: »
    If your 12v coolers are Peltier junction coolers you are already throwing away a lot of power for cooling.

    You could series connect the 2, 12V gadgets if they are identical, and run form 24V.
    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 ,

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Best way to convert voltage?
    mike90045 wrote: »
    You could series connect the 2, 12V gadgets if they are identical, and run from 24V.
    Hmmm... About the only appliances I would series connect would be filament light bulbs...

    Filament lamps are one of the few products out there that, roughly, run as constant current loads.

    Most of our other appliances are closer to Constant Power devices (electronics, motor driven loads, florescent lamps, etc.)...
    • P=I*V
    If you have two 12 volt devices in series sharing a 24 volt source... say 5 amps * 12 volts = 60 watts...

    And one device decides it needs a bit more current (load went up). Now, it share of the 24 volts will drop. But, since it needs the same power, current must go up to compensate. Causes voltage to drop more... "positive feed back loop"... Basically, you have the beginnings of a very large and expensive "digital flip flop". The voltage of one device will crash to zero... And the other one, seeing is voltage rise, will reduce current flow--worsening the operating voltage for the first device... The second device now sees near 24 volts--and fails.

    Don't do it...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 7,286 ✭✭✭✭
    Re: Best way to convert voltage?
    BB. wrote: »
    ....Basically, you have the beginnings of a very large and expensive "digital flip flop". The voltage of one device will crash to zero... And the other one, seeing is voltage rise, will reduce current flow--worsening the operating voltage for the first device... The second device now sees near 24 volts--and fails.

    Don't do it...

    -Bill

    I guess I was thinking thermalelectric coolers. Which never seem to work well enough to cool properly, and always pull full power.
    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 ,

  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Best way to convert voltage?
    backroad wrote: »
    ....The 24v coolers say they pull about 130 watts each and I had planned on running two.

    What kind of 24vdc coolers draw 130 watts each? That's almost as much as a full sized refridgerator/freezer.
  • solarvicsolarvic Solar Expert Posts: 1,043 ✭✭✭
    Re: Best way to convert voltage?
    RCinFLA wrote: »
    What kind of 24vdc coolers draw 130 watts each? That's almost as much as a full sized refridgerator/freezer.

    Yes my sears 18 cubic foot only uses 90 watts @125v S8)larvic
  • backroadbackroad Solar Expert Posts: 185 ✭✭✭✭✭
    Re: Best way to convert voltage?

    When I said "COOLERS", I meant swamp coolers from solar chill. I'm currently using a couple of standard evaporative coolers that are converted to 12v motors, but still using 120v water pumps.

    The water pump that i was referring to is a shurflo drawing 6 amps.

    Maybe this helps a bit.


    My current thinking is to go with one of the Iota regulated chargers in the 25 amp range. They also offer a 15 and a 40 amp.
  • MenaMena Registered Users Posts: 4
    in my eyes, I though power converter can just converts AC power to DC power or DC power to AC power like power inverter. Here I know there are also DC to DC power converter. I wanna know is there a kind of converter that can convert DC 12V to DC 24V? 
  • BB.BB. Super Moderators Posts: 26,837 admin
    Yes, those are called "boost converters" (boost converters "raise voltages" and buck converters "drop voltages". Then there are buck/boost converters that can do both).

    A quick place to start is EBay and search for "dc to dc boost converter". That will get you started.

    You do need to know how much current at 24 VDC you will want (i.e., 5 amps * 24 volts = 120 Watt converter). They generally run around 85% to 95% efficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 859 ✭✭✭✭
    Also note that a lot of the low cost ebay stuff is optimistically rated.  Ie, if you need 5 amps, consider buying one rated for 10A.
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