48 to 12v with Heating Pads connection

[wtrey613]

All, See attached proposed diagram for connecting Heating pad for my Lithium phosphate batteries

I bought at 48v to 12v step down converter, it comes with a 20 amp fuse connected to the 48v hot side.
We already have 2x 48v batteries but our problem is that they get very cold during the winter months and we need to keep them heated.
We bought TWO Facon 13.5V 65watt heating pads we would like to attach to our batteries. (Attach in Parallel)

Any thoughts on this? not sure if i've missed anything with this set up. the heating pads should shut off at 68F and turn on at 45F.

Is there a wiring diagram or any other videos i could look at to get a guide? i just don't have the confidence for this at this time.
Again, a bit of a novice here. would love some help/feedback

48-12v link
facon water heating pad

 

[MisterSandals]

We bought TWO Facon 13.5V 65watt heating pads we would like to attach to our batteries. (Attach in Parallel)

You should attach the heating pads to the output of the 48V to 12V converter (as pictured in your attached PDF).
Is there temperature control built into the heating pads or how do you expect to control turning the heating on and off?
Or will you manually turn them on and monitor the temperature of your batteries?

 

[MurphyGuy]

You might want to consider dumping the 48v-12v converter and just using 4 smaller 12vdc heaters wired in series. Far more reliable and efficient that way.

 

[MisterSandals]

Far more reliable and efficient that way.

Really? If one failed, it would bring down the other 3 if all in series. And, if i'm trying to warm batteries, i'd rather have some redundancy.

But yes for efficiency if running directly without a converter at 48V series.

Not sure I've seen 24v or 48V tank heaters or the likes (i did a quick search on Amazon and did not see any on the first page of results).

 

[OffGridInTheCity]

I use several 48vdc -> 12vdc converters with good success. Heat pads under my batteries in my camp trailer are one example. Agree with @MisterSandles, they're wired in parallel

I don't notice what I would consider significant conversion losses with converters like this - https://www.amazon.com/360W-Converter-Voltage-Regulator-Waterproof/dp/B07J274LZD/ref=sr_1_2 This one says ".....High Conversion Efficiency: up to 96%...." which means 4% loss? So a 68w heating pad would require 71w of power - e.g. 3w loss.

Maybe someone has actual specs - I'd be interested to see them.

 

[MurphyGuy]

Really? If one failed, it would bring down the other 3 if all in series. And, if i'm trying to warm batteries, i'd rather have some redundancy.

But yes for efficiency if running directly without a converter at 48V series.

Not sure I've seen 24v or 48V tank heaters or the likes (i did a quick search on Amazon and did not see any on the first page of results).

Heaters almost never fail. 500 voltage converters will usually fail for every heater that fails.

Heaters have a higher failure rate when they are operating at higher temperatures, like those in water heaters, space heaters, or kilns. For a heater on a battery bank that never really gets hot to begin with, the failure rate is ridiculously low, almost zero.

Far more common is the failure of the controller, or in this case, failure of the voltage converter.

 

[MisterSandals]

Far more common is the failure of the controller, or in this case, failure of the voltage converter.

Agreed in terms of the heating element.

However, in the heat pads the OP is considering, each has a temp controller, which as you indicate (I trust your assessment), is far more common to failure (than the heating element).
So if one temp controller fails, I suspect all others in series would be brought down (it likely depends on the nature of the failure and how the power series is wired). Definitely lower redundancy.

 

[MurphyGuy]

Agreed in terms of the heating element.

However, in the heat pads the OP is considering, each has a temp controller, which as you indicate (I trust your assessment), is far more common to failure (than the heating element).
So if one temp controller fails, I suspect all others in series would be brought down (it likely depends on the nature of the failure and how the power series is wired). Definitely lower redundancy.

I think his choice of heater pad device is not what I would have gone with.

I would have probably gone with either a 2 inch wide carbon fiber cloth-tape or some heat trace cable like the type they use in gutters or to keep water pipes from freezing.
The carbon fiber would be my preferred choice since it is intrinsically safe when cut to the right length.

With 48vdc systems, you can wire up regular 120 volt AC heater elements and they work just fine, albeit at a slightly lower power level..

I would also suggest using a snap disc switch/thermostat with a high level snap-disc in series just in case. And you'd have to put a gun to my head to get me to install a cheap Chinese heater.. heck no.. no way, not even in a dream would I allow that piece of crap Falcon heater to keep my batteries warm while unsupervised. If that thermostat welds itself closed, his batteries are going to be hard boiled at best, and burn his house down at worst.

About the only positive thing here is that it's a 12x18 pad with only 65 watts going through it... the energy density seems pretty safe on that front, but that's also assuming the entire pad is used and its not just a few hot spots within the pad. You can never trust the junk made in China, its a gamble every time.

 

[MisterSandals]

snap disc switch/thermostat

Cool, I learned something today, thanks.

I came across this product in my search results (on at 35F, off at 45F):

https://www.amazon.com/Thermostat-Switch-Circuit-Large-Flange/dp/B0026S6WGK

Sorry for the slight detour…

I use a cheapo thermostat for our seed trays (works flawlessly, started as a test prototype but it did the job). Will cut over to a snap disc (~75F) to make it safer.

 

[time2roll]

All, See attached proposed diagram for connecting Heating pad for my Lithium phosphate batteries

I bought at 48v to 12v step down converter, it comes with a 20 amp fuse connected to the 48v hot side.
We already have 2x 48v batteries but our problem is that they get very cold during the winter months and we need to keep them heated.
We bought TWO Facon 13.5V 65watt heating pads we would like to attach to our batteries. (Attach in Parallel)

Any thoughts on this? not sure if i've missed anything with this set up. the heating pads should shut off at 68F and turn on at 45F.

Is there a wiring diagram or any other videos i could look at to get a guide? i just don't have the confidence for this at this time.
Again, a bit of a novice here. would love some help/feedback

48-12v link
facon water heating pad

Diagram and equipment look good. Make the connections and let it rip.
Will get slightly lower heat as the supply voltage is about 10% lower than pad rating. Maybe 20% lower heat. I would not worry about it.

 

[MurphyGuy]

Cool, I learned something today, thanks.

I came across this product in my search results (on at 35F, off at 45F):

https://www.amazon.com/Thermostat-Switch-Circuit-Large-Flange/dp/B0026S6WGK

Sorry for the slight detour…

I use a cheapo thermostat for our seed trays (works flawlessly, started as a test prototype but it did the job). Will cut over to a snap disc (~75F) to make it safer.

Snap discs are super reliable. Pretty much every clothes dryer ever made has three or four of them inside. Don't waste your time though, they're all set for really high temperatures.

If you install them in a DIY project, you have to make sure that 1) it has good contact with the surface you are monitoring and 2) there must be some insulating value around the outside edges for it to work accurately. Good insulation isn't required, but some type of insulation is. A lot of manufacturers will seat them into a plastic cradle and allow the cradle to provide the insulation. A 3d printer would come in handy for that.

 

[wtrey613]

You should attach the heating pads to the output of the 48V to 12V converter (as pictured in your attached PDF).
Is there temperature control built into the heating pads or how do you expect to control turning the heating on and off?
Or will you manually turn them on and monitor the temperature of your batteries?

SO the heating pads Kick on at 45 degrees and kick off at 68 degrees. I may install an additional temperature on/off switch see below
Switch
that way They will default to this if the internal temperature module craps out

 

[wtrey613]

Cool, I learned something today, thanks.

I came across this product in my search results (on at 35F, off at 45F):

https://www.amazon.com/Thermostat-Switch-Circuit-Large-Flange/dp/B0026S6WGK

Sorry for the slight detour…

I use a cheapo thermostat for our seed trays (works flawlessly, started as a test prototype but it did the job). Will cut over to a snap disc (~75F) to make it safer.

SO with the snap disk, i am not sure how i would wire that or where to place that? It would have to be in our open battery box but the temp of the box could be lower that the actual batteries where the heating pads are attached....
again just not sure where i would wire it in so the heat would be felt on the snap ....

 

[wtrey613]

You might want to consider dumping the 48v-12v converter and just using 4 smaller 12vdc heaters wired in series. Far more reliable and efficient that way.

So something like this?? if so what type of amp Breaker? a 20 amp Breaker? or something bigger? it should only be 5 amps with the circuit.

 

[MurphyGuy]

So something like this?? if so what type of amp Breaker? a 20 amp Breaker? or something bigger? it should only be 5 amps with the circuit.

Yup.
The current draw through a single heater will be the same when you connect 4 in series. So if one of the 12v heaters is rated for 5 amps, then it will still be 5 amps when all 4 are connected to a 48 volt source.

The only caveat to this would be the fact that you're not really hooking a 48 volt source to a series of 12 volt heaters, your lithium battery source can actually be as high as 56 volts or more. As you increase voltage, the current draw from the heaters will also increase. Ohms law not very forgiving.

 

[wtrey613]

I think his choice of heater pad device is not what I would have gone with.

I would have probably gone with either a 2 inch wide carbon fiber cloth-tape or some heat trace cable like the type they use in gutters or to keep water pipes from freezing.
The carbon fiber would be my preferred choice since it is intrinsically safe when cut to the right length.

With 48vdc systems, you can wire up regular 120 volt AC heater elements and they work just fine, albeit at a slightly lower power level..

I would also suggest using a snap disc switch/thermostat with a high level snap-disc in series just in case. And you'd have to put a gun to my head to get me to install a cheap Chinese heater.. heck no.. no way, not even in a dream would I allow that piece of crap Falcon heater to keep my batteries warm while unsupervised. If that thermostat welds itself closed, his batteries are going to be hard boiled at best, and burn his house down at worst.

About the only positive thing here is that it's a 12x18 pad with only 65 watts going through it... the energy density seems pretty safe on that front, but that's also assuming the entire pad is used and its not just a few hot spots within the pad. You can never trust the junk made in China, its a gamble every time.

Wait so what do you mean by wiring a regular 120 volt AC heater elements? could you give an example? Is that like wiring a heating pad i would plug into my house, stripping the wires and then hooking it up directly to the Bus bar? Also, any recommendations to heaters/heating pads that aren't Chinese made?

Yup.
The current draw through a single heater will be the same when you connect 4 in series. So if one of the 12v heaters is rated for 5 amps, then it will still be 5 amps when all 4 are connected to a 48 volt source.

The only caveat to this would be the fact that you're not really hooking a 48 volt source to a series of 12 volt heaters, your lithium battery source can actually be as high as 56 volts or more. As you increase voltage, the current draw from the heaters will also increase. Ohms law not very forgiving.

So in this case, if my batteries are running at say 52 Volts.... would that ruin the heating pads? or they would run at a higher voltage? if you could clarify that would be great!

 

[MurphyGuy]

Wait so what do you mean by wiring a regular 120 volt AC heater elements? could you give an example? Is that like wiring a heating pad i would plug into my house, stripping the wires and then hooking it up directly to the Bus bar? Also, any recommendations to heaters/heating pads that aren't Chinese made?

So in this case, if my batteries are running at say 52 Volts.... would that ruin the heating pads? or they would run at a higher voltage? if you could clarify that would be great!

Heater elements are resistive, which means you can pump ac or dc current through them. Since lithium batteries in the 52 to 56 volt range are almost half of 120 volts AC is, the heater will still put out about 25% of its rated power. Then figure in the fact you're going from AC to DC, and the heater will put out even more power.

If your heater is rated for 4x12v = 48 volts and you start pumping in 52 volts, a 65 watt heater will be more in the range of 70 watts. As voltage goes up, so does current through the resistive load.

If your battery has a full charge at 56 volts, it gets even worse as your 65 watt heater will probably pump out about 75 watts. If you're running in a high temp environment, it is likely to shorten the life of the heater. Heating a battery in the cold of winter, probably not a big deal.

 

[justgary]

Then figure in the fact you're going from AC to DC, and the heater will put out even more power.

Probably not since "120V AC" is 120V RMS, or equivalent DC voltage. Peak voltage on "120V AC" is 1.41 times higher, or around 170 volts.

I like this solution the best since it has one heater pad. It does still need a thermostat, but the snap disc sounds like the solution to that (provided it is rated to switch 50VDC).

 

[wtrey613]

I use several 48vdc -> 12vdc converters with good success. Heat pads under my batteries in my camp trailer are one example. Agree with @MisterSandles, they're wired in parallel

I don't notice what I would consider significant conversion losses with converters like this - https://www.amazon.com/360W-Converter-Voltage-Regulator-Waterproof/dp/B07J274LZD/ref=sr_1_2 This one says ".....High Conversion Efficiency: up to 96%...." which means 4% loss? So a 68w heating pad would require 71w of power - e.g. 3w loss.

Maybe someone has actual specs - I'd be interested to see them.

question on this, the wire used to connect From the 48v bus bar to the 48v-12v converter... is there a certain gauge i need for the high voltage?
The converter has 16 gage wire... My batteries to the bus bar to my growatt are all 2 AWG.... SO should i just stick with 16 Gage?

 

[OffGridInTheCity]

question on this, the wire used to connect From the 48v bus bar to the 48v-12v converter... is there a certain gauge i need for the high voltage?
The converter has 16 gage wire... My batteries to the bus bar to my growatt are all 2 AWG.... SO should i just stick with 16 Gage?

The wire size on the converter is perfectly adequate. Let's say you buy a 30a@12v converter - e.g. 360w max. 360w / 48v = 7.5a max which means 16awg is reasonable.