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Old 09-17-2021, 02:40 PM   #1
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Small Pet Heater for Under Thin bed

Our 16 year old cat gets pretty grumpy when it gets cold but is far too proud to let us cover him with anything. So, he chooses to jump around all night making sure we can't sleep either.

Here is a super cheap and easy way to heat a bed for a cat or small dog. These pads are available on Amazon, https://www.amazon.com/dp/B075WVPP5Y...roduct_details 4 for $20.

I hooked two pads in series to a standard 12V plug wire (cigarette lighter plug, also available on Amazon or Ebay for cheap). Plug into your interior 12V socket outlet.

The two pads together get very warm, almost too hot to touch but a great temperature if under something like a fleece blanket and will heat a small area. They use 14 watts total, just slightly over one amp. Running on a typical winter night might cost 10-12 Ah from your battery. I like that the pads can be placed separately such that some areas can be warmer than others. If more heat or a bigger heated area is needed, you could hook the other two panels in series as well and then join both sets in parallel - 2A total.

Warm happy cat = better sleep for everybody!
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Old 09-17-2021, 07:18 PM   #2
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A question, please.
Stamped on the pads is 25 watts.
You measure 14 watts total.

Please clarify.

I’m looking for something to keep lithium batteries warm during sub-freezing temperatures. These look promising.
Lots of the comments on Amazon indicate that is a common use for this product.

I know nothing about electricity. With that said, could I put an alligator clip on each wire and simply clip those to the appropriate battery terminal as needed? Wouldn’t be 12 volts but might be warm enough. Maybe.
Thank you
Ed
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Old 09-17-2021, 08:11 PM   #3
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Originally Posted by EdColorado View Post
A question, please.
Stamped on the pads is 25 watts.
You measure 14 watts total.

Please clarify.

I’m looking for something to keep lithium batteries warm during sub-freezing temperatures. These look promising.
Lots of the comments on Amazon indicate that is a common use for this product.

I know nothing about electricity. With that said, could I put an alligator clip on each wire and simply clip those to the appropriate battery terminal as needed? Wouldn’t be 12 volts but might be warm enough. Maybe.
Thank you
Ed
Hi Ed, by hooking them in series, the power is cut in half. So, I think if everything were measured very accurately it would probably be 12.5 watts, if the 25 watts per pad is accurate and it seems like it is.

I am also thinking of using these to warm LFP batteries. You'd need a temperature controlled off/on. I am leaning towards using a Morningstar RD-1 relay driver. It's very nice because it can drive 4 different relays on user programmed values for voltage and it has an internal temperature sensor which can also be used to trigger a relay. That makes it perfect for turning pads off/on and also operating relays for high and low voltage cutoffs if you need that. The RD-1 puts out a low current so I will pair that with a small relay (cheap on Amazon, I can provide link if this interests you) which will be able to connect and disconnect the current to the pads.

The electrical hook ups are very simple and I can also help you with that if you want.
In terms of hooking directly to the battery, it will work because the battery voltage is fine but there will be no circuit protection. An advantage of the cigarette lighter plug is that it has a small internal (replaceable) fuse to provide circuit protection.

Let me know if I can help you with this stuff.
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Old 09-17-2021, 08:12 PM   #4
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You might want to have a means of regulating the temp on that.............comments indicated 155 degrees F.
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Old 09-17-2021, 08:17 PM   #5
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I should mention that I first hooked two in parallel but they got too hot in my opinion. I wouldn't feel comfortable leaving them on overnight in a cat bed.
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Old 09-17-2021, 08:24 PM   #6
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You might want to have a means of regulating the temp on that.............comments indicated 155 degrees F.
I think even hotter than that, I think I read 195 or a bit higher. When I hooked them in parallel (each at full power) they got too hot to touch. In series, they were hot but not too hot to hold, I'd guess between 105 and 110. I will take a temp sensor and try to measure when I get a chance. I like the simplicity of not having to regulate them but we'll see.
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Old 09-17-2021, 09:08 PM   #7
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“ I like the simplicity of not having to regulate them but we'll see.”

Your great solution in post #3 is way past my electronic pay grade.

Wondering.

Two in series to keep the temperature down plus a 3 amp fuse and alligator clips.
I would only use this when the trailer was in storage and the weather guessers we’re thinking of temps in the teens.

Thoughts?
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Old 09-17-2021, 09:22 PM   #8
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Quote:
Originally Posted by EdColorado View Post
“ I like the simplicity of not having to regulate them but we'll see.”

Your great solution in post #3 is way past my electronic pay grade.

Wondering.

Two in series to keep the temperature down plus a 3 amp fuse and alligator clips.
I would only use this when the trailer was in storage and the weather guessers we’re thinking of temps in the teens.

Thoughts?

Sure, I definitely understand that. I don't see any reason your proposal wouldn't work. I think especially if you had some insulation around the battery to keep the heat in, 14 watts should help. You could also consider doing them in parallel (same as two individual pads) because 25 watts would probably be ok. I am wondering about just getting an old 25 watt incandescent light bulb and using that to heat the area? You have 120V power to where it's stored?
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Old 09-17-2021, 09:38 PM   #9
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I
I am wondering about just getting an old 25 watt incandescent light bulb and using that to heat the area? You have 120V power to where it's stored?”

Thank you, thank you. What a wonderfully simple solution. I’ll have the lithium batteries plus an inverter. Plenty to run a small lightbulb all night as needed. I can even put a timer on the bulb. That’s in my skill set.

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Old 09-17-2021, 11:08 PM   #10
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Originally Posted by EdColorado View Post
Two in series to keep the temperature down plus a 3 amp fuse and alligator clips.
I would only use this when the trailer was in storage and the weather guessers we’re thinking of temps in the teens.

Thoughts?
The only limitation with lithium is charging below freezing. The integral BMS should protect from that. If you are in storage just disconnect/minimize your loads and the lithium should be fine. You can discharge and store at some pretty low temperatures. Check your battery specs. If the heat source is powered directly off the battery bank or via inverter you will eventually deeply discharge the lithium which would be worse than just disconnecting it. Unless of course you have solar that can keep up with the demand on a daily basis through a long cold spell.
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Old 09-18-2021, 12:00 AM   #11
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The only limitation with lithium is charging below freezing. The integral BMS should protect from that. If you are in storage just disconnect/minimize your loads and the lithium should be fine. You can discharge and store at some pretty low temperatures. Check your battery specs. If the heat source is powered directly off the battery bank or via inverter you will eventually deeply discharge the lithium which would be worse than just disconnecting it. Unless of course you have solar that can keep up with the demand on a daily basis through a long cold spell.
Thank you. Everything you say is exactly what the installer says about storage.
The battery literature says the battery is good down to -4F.
On the odd occasion, we get temperatures well below that plus I’ll start to get nervous when the temperature gets into the teens. Who knows just how accurate that -4* is? I was looking for a worse case scenario solution. I’ll have sufficient solar and battery storage so I should be just fine with the simple light bulb solution.

Thank you for your ideas.

Ed


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Old 09-18-2021, 01:01 AM   #12
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Hi Ed, by hooking them in series, the power is cut in half. So, I think if everything were measured very accurately it would probably be 12.5 watts, if the 25 watts per pad is accurate and it seems like it is.
Connecting them in series cuts the voltage to each pad in half, and the power for each pad to one quarter of what the pad would be by itself. So the power (if 25 W per pad at 12 V) would be 6.25 W each; that's 12.5 W total for two, instead of 50 W total for two in parallel. Maybe that's what you meant (12.5 W for two).

Resistance depends on temperature, so it won't actually be simply 1/4 power at 1/2 voltage.
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Old 09-18-2021, 01:13 AM   #13
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A question, please.
Stamped on the pads is 25 watts.
You measure 14 watts total.

Please clarify.
If rated at 24 watts each @ 12 V (to make the math of the example easier), they would have a resistance of 6 ohms... meaning that a current of 2 A at 12 V or 1 A at 6 V (because current = voltage / resistance). The power for each pad at 6 V is 6 watts (because power = current x voltage, or power = voltage squared / resistance).

They're actually rated at 25 watts each (not the 24 of my example), the actual voltage is probably over 12 V, and resistance is probably different at the lower temperature resulting from half voltage, so 12 W or 14 W... close enough.
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Old 09-18-2021, 07:38 AM   #14
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Connecting them in series cuts the voltage to each pad in half, and the power for each pad to one quarter of what the pad would be by itself. So the power (if 25 W per pad at 12 V) would be 6.25 W each; that's 12.5 W total for two, instead of 50 W total for two in parallel. Maybe that's what you meant (12.5 W for two).

Resistance depends on temperature, so it won't actually be simply 1/4 power at 1/2 voltage.
Thank you for putting the number to it, that is what I meant.

I agree with Rubicon as well that the battery on its own should be fine. I don't know if there is a temperature cutoff for storage or it's simply a charging issue. It's also clear that if the battery is down close to freezing, but still above the cutoff, it should be charged very slowly. That means that leaving a trailer plugged into shore power in cold temps might not be a great idea. And these batteries don't need to be kept full, and in fact should not be full in storage.



The lightbulb on inverter should work if there is a real danger of damaging low temps (if that's even an issue) but a big 1500W inverter is so inefficient at low loads that it would definitely use lots more than 25 watts. Ed would definitely need to keep an eye on battery level to ensure it doesn't discharge below 30% or so.



As mentioned above (since we've gone off to lithium land), it is not a good idea to put these batteries into storage at full charge. Typical recommendation is that they be between 30-70% charge if they are not being cycled. What works for me is to charge it up before a trip and then run the frig on DC on the way home to get it back down under 80% SOC by the time it gets mothballed for a few weeks again.
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Old 09-18-2021, 08:01 AM   #15
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I appreciate all the comments.
Lithium is new to me. I’m reading everything I can come across about good maintenance practices. At the cost per battery, A fatal error is quite expensive.

Now I’m thinking perhaps a portable Buddy Heater for those rare occasions of potentially damaging temperatures. They cost a fraction of a new battery.

Thanks again.

Ed
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Old 09-18-2021, 08:29 AM   #16
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I appreciate all the comments.
Lithium is new to me. I’m reading everything I can come across about good maintenance practices. At the cost per battery, A fatal error is quite expensive.

Now I’m thinking perhaps a portable Buddy Heater for those rare occasions of potentially damaging temperatures. They cost a fraction of a new battery.

Thanks again.

Ed

I agree it's quite a learning curve, but so worth it, imo. If you come across something definitive about low temp problems in storage (not charging), please post it because as Rubicon Dave mentioned, the issues I have seen are with charging the battery at or below freezing.
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Old 09-18-2021, 08:32 AM   #17
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“As mentioned above (since we've gone off to lithium land), it is not a good idea to put these batteries into storage at full charge….”


And that’s another point where I read conflicting opinions from trusted sources.

Progressive Dynamics.

https://www.progressivedyn.com/frequ...hium-charging/

How Should I Store My RV Lithium Battery During the Winter?

Another advantage of Lithium Iron Phosphate Batteries is that they do not require a trickle charge during long periods of storage. In fact, disconnecting the charger during winter storage or long term inactivity and allowing the battery to rest is actually beneficial and will improve long term battery life. Before putting your RV into winter storage, simply connect it to 120 VAC power for up to 10 hours for large battery packs and fully charge the battery, then remove AC power and hit the battery disconnect switch. In the spring it will be ready to accept a full charge before your first camping trip. Lithium Batteries have a very low self discharge rate and only loose 2 to 4% of their charge per month.“
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Old 09-18-2021, 06:57 PM   #18
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“As mentioned above (since we've gone off to lithium land), it is not a good idea to put these batteries into storage at full charge….”


And that’s another point where I read conflicting opinions from trusted sources.

Progressive Dynamics.

https://www.progressivedyn.com/frequ...hium-charging/

How Should I Store My RV Lithium Battery During the Winter?

Another advantage of Lithium Iron Phosphate Batteries is that they do not require a trickle charge during long periods of storage. In fact, disconnecting the charger during winter storage or long term inactivity and allowing the battery to rest is actually beneficial and will improve long term battery life. Before putting your RV into winter storage, simply connect it to 120 VAC power for up to 10 hours for large battery packs and fully charge the battery...“
I see the conflict, but I would not consider Progressive Dynamics a trusted source regarding lithium-ion batteries... since they don't make or even sell them. On the other hand, while starting storage at a lower state of charge (than fully charged) is better, starting at fully charged is certainly better than starting at nearly discharged - I wouldn't worry about it.
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Old 09-19-2021, 07:43 AM   #19
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I see the conflict, but I would not consider Progressive Dynamics a trusted source regarding lithium-ion batteries... since they don't make or even sell them. On the other hand, while starting storage at a lower state of charge (than fully charged) is better, starting at fully charged is certainly better than starting at nearly discharged - I wouldn't worry about it.
Agreed.
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Old 09-19-2021, 12:50 PM   #20
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been discussing offline with Ed but i thought this might be useful generally. as to why GoPower and other manufacturers still say their banks need to be above -4F, my only guess is that because they cannot ensure a user won't charge or discharge below that temp, they provide that limit for storage to be super conservative. i have found nothing reliable that indicates the batteries cannot be stored at very low temps. Brian B-P knows a lot about the differences and advantages/limitations of the various lithium battery types and hopefully he'll weigh in.
here's a summary from solacity:
https://www.solacity.com/how-to-keep...tteries-happy/


Storing Lithium-Ion Batteries


The very low self-discharge rate makes it easy to store LFP batteries, even for longer periods. It is no problem to put a lithium-ion battery away for a year, just make sure there is some charge in it before placing it in storage. Something between 50% – 60% is ideal, that will give the battery a very long time before self-discharge brings the Voltage close to the danger point.
Storing batteries below freezing is fine, even at very low temperatures such as -40 Centigrade (that is the same in Fahrenheit), or even less! The electrolyte in LiFePO4 cells does not contain any water, so even when it freezes (which happens around -40 Centigrade, depending on the particular formulation) it does not expand, and does not damage the cells. Just let the battery warm up a bit before you start discharging it again, which is OK at -20 Centigrade and above. You will see an apparent loss of capacity when discharging at below-freezing temperatures that reverses when the battery gets above freezing, and there is a slightly accelerated effect on aging. Storing them at low temperatures is certainly much better than storage at high temperatures: Calendar aging slows down dramatically at low temperatures. Try to avoid storing them at 45 Centigrade and above, and try to avoid storing them completely full if possible (or nearly empty).
If you need to store batteries for longer periods, be sure to simply disconnect all wires from them. That way there can not be any stray loads that slowly discharge the batteries.
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