Powering two Steca fridge/freezers from a 48 volt battery bank

ajagman1ajagman1 Posts: 3Registered Users
I have two Steca fridge/freezers that run on 12 or 24 volts and was wondering what the best way was to power them from a 48 volt battery bank.
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  • jcheiljcheil Posts: 719Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    You would need to get a voltage converter to go from 48vdc to 24vdc.

    There are lots of somewhat cheap ones ($30) but they will only handle a very small amount of current and I seriously doubt they would run your fridge/freezers.

    The higher power ones are in the several hundred dollar price range. At that point, in my opinion, you could just go out and but a new energy efficient 110v fridge/freezer and save the hassle.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    jcheil wrote: »
    You would need to get a voltage converter to go from 48vdc to 24vdc.

    There are lots of somewhat cheap ones ($30) but they will only handle a very small amount of current and I seriously doubt they would run your fridge/freezers.

    Why not? The danfoss compressor only draws about 4-6 amps at 12 volts or 2-3 amps at 24 volts. They do not have startup surges like conventional AC fridges.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jcheiljcheil Posts: 719Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    vtmaps wrote: »
    Why not? The danfoss compressor only draws about 4-6 amps at 12 volts or 2-3 amps at 24 volts. They do not have startup surges like conventional AC fridges.

    --vtMaps

    Because I don't know what the ratings are on his equipment...but the small converters I briefly looked at for that cheap price only handle like 5 amps. I guess I just figured if my little shurflo was drawing 7-8 amps that his compressor would certainly draw more.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    jcheil wrote: »
    Because I don't know what the ratings are on his equipment...but the small converters I briefly looked at for that cheap price only handle like 5 amps. I guess I just figured if my little shurflo was drawing 7-8 amps that his compressor would certainly draw more.

    The Steca spec sheet claims it draws MAX of 100 watts. At 24 volts that would be less than 5 amps. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jcheiljcheil Posts: 719Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Well then in that case he only has $30 to waste if it doesn't work :)
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • mmagmmag Posts: 57Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    is it possible to wire them both in series straight from the batteries?
  • BB.BB. Posts: 27,444Super Moderators admin
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    I would not... Too many unknowns and compressors tend to have high starting current--If one "starts before" the other, then you will have unbalanced voltage across the motors. Motors tend to be non-linear (lower voltage/higher current).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Trying to run 2 12/24v fridges off a 48v battery wont work of course if connected in series.
    The only way to do it is buy a 48 to 12 or preferably 24v voltage converter. 30a if 12v and 20a if 24v.
    I would buy 2 x48 to 24 v 10a ones.. more reliable and most likely cheaper than a 2oa single one. and you can use smaller wiring..
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    BB Iguarantee that 97.62 % (approx give or take 10 cents .)of the time they would try to start at different times.
  • BB.BB. Posts: 27,444Super Moderators admin
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    I guessed that he would put the thermostats in parallel so that both pumps and freezers would start/stop "at the same time" when either freezer needs cooling.

    In theory, the two thermostats would be in series in the 48 volt connection (not looking at thermostat maximum working voltage ratings)--So only when both freezers need cooling would the circuit be on--If one need cooling and the other does not--Then both will be off (the old logic And vs Or function.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    BB. wrote: »
    I guessed that he would put the thermostats in parallel so that both pumps and freezers would start/stop "at the same time" when either freezer needs cooling.

    Those Steca units have electronic controls. I expect you will need an external thermostat (like those used in freezer conversions) if you want to do that. Also, I suspect the units will not work properly if hooked in series.... upon startup the danfloss compressor self configures for 12 or 24 volts. They have two low voltage disconnects (depending on 12 or 24 volts). They also have proportional control of the compressor motor.

    I predict that at best they will not work properly. I think its quite possible that you will damage them if you put them in series. If you call Steca to ask about this, please let us know what they say.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CDN_VTCDN_VT Posts: 491Solar Expert ✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Here is my BF, Use a morningstar MPPT 15 on a 24 volt battery setup & the 48 volt system keeps the 24 volt system up ..
  • ajagman1ajagman1 Posts: 3Registered Users
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    CDN_VT wrote: »
    Here is my BF, Use a morningstar MPPT 15 on a 24 volt battery setup & the 48 volt system keeps the 24 volt system up ..
    That was my thought and I have a brand new one in the box here but was told by NAWS that it would not work. I am tempted to try it but if it doesn't work I will be out $223.00.
  • BB.BB. Posts: 27,444Super Moderators admin
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    The MorningStar MPPT should work--But it would do it by charging your smaller/ 12 or 24 volt battery from your 48 volt source. You cannot/should not run the MPPT charge controller without a "buffering" 12/24 volt battery bank. The controller will not work as a "down converter" by itself.

    This adds the cost of the controller plus that of a second (albeit smaller) "low voltage" battery bank to run the DC refrigerator/freezers--And all the losses/costs that entails (a second battery bank that will need watering and eventual replacement down the road).

    Of course, you can go with a 48 volt to 24 or 12 volt DC to DC down converter (costs and around ~85% efficiency) that is rated to support the DC loads (and surge current).

    Is this better than just going with a 48 to 120 VAC inverter and an energy star rated cold box? Only you can decide that one.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ajagman1ajagman1 Posts: 3Registered Users
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Just to let everyone know, I tried the morningstar MPPT 15 with a 12 volt battery and it has been working great.
  • zonebluezoneblue Posts: 1,218Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    vtmaps wrote: »
    Why not? The danfoss compressor only draws about 4-6 amps at 12 volts or 2-3 amps at 24 volts. They do not have startup surges like conventional AC fridges.
    --vtMaps

    Those danfoss compressors are a thing of beauty alright. But they do have start up surges, at one sec sample rate I occasionally see 350W or so.

    Attachment not found.

    72.5W @27% there. I have seen it run as low as 370Wh/day. And its not even one of the thicker insulation models.
    mmag wrote: »
    is it possible to wire them both in series straight from the batteries?

    Forget it. That will fail horribly.

    There arent that many 48-12 VDC converters, but another approach you could try if you are attached to those Stecas, is a 120AC - 24V power supply. Take a wander through these;
    http://www.ebay.com/bhp/24v-power-supply
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    zoneblue wrote: »
    Those danfoss compressors are a thing of beauty alright. But they do have start up surges, at one sec sample rate I occasionally see 350W or so.

    Interesting... how much energy under those spikes? It the spike is narrow enough I don't see why a DC to DC converter will not work. I guess that like everything else it needs to be tested.
    zoneblue wrote: »
    72.5W @27% there.

    huh? what is 27% ? Is that the duty cycle? If so, the fridge is drawing 470 watthours per day. Very good!

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zonebluezoneblue Posts: 1,218Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    I dunno vtmaps, 1 second isnt fast enough to tell much about it, only catchs it by chance from time to time. But i think you are right, theres not much to it. Also most of them have an in built converter of some sort to cope with 12 or 24 volts. I can see its heatsink, but couldnt say how it works. Tho it must be pretty simple, because when the sun comes out you can hear the compressor speed up.

    27% duty yes, at about 18*C ambient. At 30*C ambient duty goes up to 50%, which would be nearer 1000Wh/day i guess.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Hill_CountryHill_Country Posts: 91Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    I will be in almost the exact same scenario when I go off-grid. We plan on purchasing two Steca chest Fridge/Freezers (a PF240 used as a freezer and a PF166 used as a fridge). We will have a 48v system (battery bank). However, instead of using the solution suggested in this thread (i.e. a Morningstar PPT w/ a separate 12v battery bank), what do you all think of using two of these DC-to-DC step down transformers to turn the 48v system voltage down to 24 volts so the Stecas can run? See link: http://www.solarconverters.com/index.php/products/84-dc-dc-step-down-controllers-ppt/163-ppt-48-10-rxx I realize the cost is somewhat high...about $250 or so for a single DC-to-DC transformer (so $500 total for both).

    I was planning on wiring these two Steca's on separate circuits with a DC-to-DC step down transformer near the first load (so as to take advantage of the higher voltage of a 48 volt system (i.e. smaller wire size) up to that point. We will also be using some DC fans on the same DC circuits, but I don't anticipate any issues as the fans draw a max of 0.78 amps at 24 volts on high speed (Nextek Vari-Cyclone fans).

    Thoughts or comments on this?
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    However, instead of using the solution suggested in this thread (i.e. a Morningstar PPT w/ a separate 12v battery bank), what do you all think of using two of these DC-to-DC step down transformers to turn the 48v system voltage down to 24 volts so the Stecas can run?

    I would definitely choose the DC to DC step down over an additional battery bank (I would do almost anything to avoid another battery). Solar Converters makes high quality products.

    But... why have a DC fridge when AC fridges can be just as efficient and much less expensive?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jcheiljcheil Posts: 719Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    vtmaps wrote: »
    But... why have a DC fridge when AC fridges can be just as efficient and much less expensive?
    --vtMaps
    I agree and I remember a few weeks ago a LONG thread about this same comparison and although the DC fridges did use less energy, it was not a significant amount and even still would be hard to justify the SIGNIFIGANT cost difference between an Ac and DC fridge. It really only comes into play if you are not going to have an inverter or if you want to just have a very small (300w) inverter such as in a 12v RV type situation.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Hill_CountryHill_Country Posts: 91Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    vtMaps, thanks for your response!

    In regards to AC vs. DC fridge/freezer and power usage...do you have any suggestions? I know the subject has been discussed heavily on these forums and the trending consensus seems to be to go the AC route because the performance gap between AC and DC has closed considerably. However, I've been looking around and can't find an AC freezer that comes close to the performance of the DC Steca PF240 in terms of energy usage. If you've found an AC freezer (or fridge, or "freezer" turned into a fridge via a thermostat) that comes close, please let me know. I'm weighing the cost of the extra solar/battery that would be necessary to run an AC freezer vs. the added cost of a DC freezer. I still feel like the DC freezer has the edge...but I'm all ears right now, as we have not purchased anything yet!
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Define "extra solar & battery".

    I designed my system specifically for the refrigerator. It also runs everything else I need. So; at 700 Watts/232 Amp hours 24 Volts is it larger or smaller than you expect to need?
  • Hill_CountryHill_Country Posts: 91Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Cariboocoot, good question!

    Although we have not purchased our system, we defined our system based on our expected loads. Inclusive in these loads are the two Steca PF240 (acting as a freezer) and PF166 (acting as a fridge). Based on Steca's published specs, our expected ambient temps., etc., it looks like our estimated daily W-h usage for the PF240 will be about 300 Wh, while the PF166 will be about 280 Wh daily. Yes, they can use more energy (higher ambient temps, opening/closing often), and they can use less energy (cooler ambient temps, not opening/closing), but this is an average and seems fair based on our anticipated usage. Most of the AC freezers that I've seen are in the 550 Wh to 850Wh daily usage range. So the difference would be anywhere from 200 Wh to 500 Wh per day in usage. On our system (estimated daily load of ~1.9 KWh/day without the fridge or freezer included) that difference would be about 10% to 26% of our system...and that's just the increase in usage. For someone with a relatively small system (our estimated usage is about 2.5 kWh/day with both Steca PF240 and PF166), small changes in loads can have a big effect.

    Now whether the cost of having the additional PV panels and battery capacity to run the AC fridge and freezer would equal the increased cost of the DC fridge and freezer, I'm not sure. I'm guessing it's close.

    Like I said, I'm open to discussion and advice...I'm still new at this and have eagerly enjoyed reading your posts, as well as the other experts on this forum for guidance and advice!
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • westbranchwestbranch Posts: 5,024Solar Expert ✭✭✭✭
     
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  • jcheiljcheil Posts: 719Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank
    Cariboocoot, good question!

    Most of the AC freezers that I've seen are in the 550 Wh to 850Wh daily usage range.

    Now whether the cost of having the additional PV panels and battery capacity to run the AC fridge and freezer would equal the increased cost of the DC fridge and freezer, I'm not sure. I'm guessing it's close.

    And remember, ambient temp has everything to do with it. My EE fridge claims 1kw per day but seems to average out to more like 1.5 per day since it is in non-ac space and higher outdoor temps.

    And IMO, unless you are trying to just use a super small inverter, better to invest in more panels. The other thing to think about is service/repair. When (if) that dc fridge breaks, you only have ONE PLACE to get parts and only certain repair techs to fix it. Which means those parts/service are at a premium. With an ac fridge there are 100's of repair places/parts available at a fraction of the cost. Again,just my opinion, but I like to keep it simple. After years and years of service, when my fridge dies in the middle of the night and needs to be replaced, I can go to Home Depot the next morning and be back up and running in couple of hours or call ANY repairperson and they can get me back up and running and likely have the parts in their van!
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • Hill_CountryHill_Country Posts: 91Solar Expert ✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Awesome, thank you westbranch! The "CEE" link looks great...I'll be taking a look.

    And jchell, thanks. You've brought up an excellent point in terms of replacement/service.
    100% Off-grid with: 8 Solarworld 275 Watt Panels, 8 Concorde SunXtender 405aH 6v AGM Batteries, MS-4448PAE 48v Inverter, MidNite Solar Classic 200 Charge Controller, 10,000 gallon rainwater collection system, etc.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    If your inverter is big enough to run an AC fridge, the inverter itself will consume a few hundred watthours every day.

    As a general rule of thumb, if your inverter is big enough to run an AC fridge, you are probably better off buying an AC fridge, and with the money you save (compared to a DC fridge) buy a couple of extra solar panels. On the other hand, if you can get by with a small inverter (very low tare losses), it might make more sense to buy a DC fridge.

    The inverter's tare losses are the same whether you run one or two AC fridges, but the cost of going DC is doubled if you buy 2 DC fridge/freezers.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Posts: 27,444Super Moderators admin
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    You need to do two paper designs and see which will be best for you...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SlappySlappy Posts: 251Solar Expert ✭✭✭✭✭✭
    Re: Powering two Steca fridge/freezers from a 48 volt battery bank

    Also keep in mind that inverters adds to a system for another point to fail. No inverter = no fridge.
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