DC-DC charger as an alternative to generator?

[crazysccrmd]

Fair enough. This is what I'm looking at getting unless someone can think of another one in a similar price range that is better:

View attachment 857182

Self-heating because it will be mounted on the outside of our trailer and we live in Colorado. I like that it has a built in SOC monitor that also works on Bluetooth.

If I'm understanding it correctly, this should mean no need for a shunt to measure SOC and power use, is that right?

Keep in mind that self heating requires constant input of power in order to heat. On cold winter nights in Colorado my self heating lithiums wouldn’t begin charging until around noon each day after several hours of solar input to power the heaters. During extended 0° periods the batteries sometimes took 10+ hours with a generator powering the trailer before they were warmed enough to accept a charge.

 

[FAW3]

Keep in mind that self heating requires constant input of power in order to heat. On cold winter nights in Colorado my self heating lithiums wouldn’t begin charging until around noon each day after several hours of solar input to power the heaters. During extended 0° periods the batteries sometimes took 10+ hours with a generator powering the trailer before they were warmed enough to accept a charge.

Thats a good observation. For a typical trailer the standard exposed plastic box on the front rails is likely not the best location for your lithium batteries. A typical rig in hard winter use would normally be heated at all times to at least a minimal freeze protection level to protect the plumbing. Inside a heated area is where you want lithium batteries even those with internal heaters.

 

[Dave in AZ]

Keep in mind that self heating requires constant input of power in order to heat. On cold winter nights in Colorado my self heating lithiums wouldn’t begin charging until around noon each day after several hours of solar input to power the heaters. During extended 0° periods the batteries sometimes took 10+ hours with a generator powering the trailer before they were warmed enough to accept a charge.

Uhm. Interesting, but it makes me want to say that your engineered solution is obviously insufficient to the task? The whole purpose of self heated setup is that the battery stays warmer than the 0f charge cutoff, at all times. Not to warm up above that the next morning. It doesn't really sound like your batteries were sufficiently self-heating to do anything?

In my mind, the absolute basics of a heated battery setup is that there is first sufficient insulation, and second sufficient heat, to keep batteries above the 0C charge cutoff. If you don't have enough of one or the other to achieve the job, it's kind of like mounting a USB fan to your car, and then complaining that it isn't much of a plane since it doesn't get airborne...

Some info on how much power they use to self heat, over say 12 hrs at some known temps, and what your battery insulation setup is, would be helpful for folks. Your report is interesting, but I need more info to make use of it. Thx!

 

[crazysccrmd]

Uhm. Interesting, but it makes me want to say that your engineered solution is obviously insufficient to the task? The whole purpose of self heated setup is that the battery stays warmer than the 0f charge cutoff, at all times. Not to warm up above that the next morning. It doesn't really sound like your batteries were sufficiently self-heating to do anything?

In my mind, the absolute basics of a heated battery setup is that there is first sufficient insulation, and second sufficient heat, to keep batteries above the 0C charge cutoff. If you don't have enough of one or the other to achieve the job, it's kind of like mounting a USB fan to your car, and then complaining that it isn't much of a plane since it doesn't get airborne...

Some info on how much power they use to self heat, over say 12 hrs at some known temps, and what your battery insulation setup is, would be helpful for folks. Your report is interesting, but I need more info to make use of it. Thx!

My assumption was you’d be mounting them on the exterior of a trailer where they’d be exposed to cold temperatures. If you put them inside the heated cabin area then self heating would not be a requirement.

The Renogy batteries use 50wh to power the heaters but if there is no incoming charge they do not heat. That’s why each night they drop in temperature since there’s obviously no solar input. An insulated box would help but without a source of heat at night the temperature would still drop before morning unless you built something extremely bulky. At that point it would be easier to just modify the trailer wiring a bit and place the batteries inside.

The charge cutoff is also not at 0°F but 0°C (32F) for lithium. Might just be a typo since you said both F and C but want to make sure. Discharge is fine at temps well below 0°F though.

 

[crazysccrmd]

Maybe better in a new tread but what do we think of the Canbat heating system ? Uses power from the charger rather than from the battery. I like these batts. They are local. But I don't like the retro price (~695 to 770USD per 100Ah, incls Can/USA shipping)

I would really like the option to locate batts outside the camper in a storage box. Even if insulated heating will still be necessary.

LOW-TEMPERATURE LITHIUM BATTERIES – LT SERIES​

Canbat Low-Temperature lithium batteries are cold-weather rated, and designed for Canada’s cold climates. The heated lithium batteries can safely charge and discharge at temperatures as low as -20°C (-4°F). How? LiFePO4 low temperature batteries have a built-in heating system featuring proprietary technology that draws power from the charger. No additional components are required. The entire process of heating and charging is completely seamless. The heating system automatically activates once charging below 0°C is attempted, and deactivates when it’s no longer needed. The heating system does not take power from the battery, but rather from the charger, ensuring the battery is not discharging itself. Plug the battery into the lithium charger and the internal heating and monitoring systems take care of the rest...

https://www.canbat.com/product-cate...battery-lifepo4/cold-weather-lithium-battery/

NO AFFILIATION

That’s how most heated lithium batteries function. They use input charging power to heat themselves rather than stored power. You have the same limitation I described - at night when temperatures drop and the batteries cold soak there is no input solar charge and you probably won’t be running your truck to keep the DC-DC charger on either. As a result the batteries don’t heat and in the morning when the sun comes up or you start your truck again it requires time to heat a cold battery before charging starts.

 

[Dave in AZ]

My assumption was you’d be mounting them on the exterior of a trailer where they’d be exposed to cold temperatures. If you put them inside the heated cabin area then self heating would not be a requirement.

The Renogy batteries use 50wh to power the heaters but if there is no incoming charge they do not heat. That’s why each night they drop in temperature since there’s obviously no solar input. An insulated box would help but without a source of heat at night the temperature would still drop before morning unless you built something extremely bulky. At that point it would be easier to just modify the trailer wiring a bit and place the batteries inside.

The charge cutoff is also not at 0°F but 0°C (32F) for lithium. Might just be a typo since you said both F and C but want to make sure. Discharge is fine at temps well below 0°F though.

Ahh yah, typo, 0C
Renogy batteries, that explains it... what a poor design choice they made there. Well, it's a poor design for what we are discussing, and absolutely the wrong battery heat design. But there are other ones.

Most self heated battery I have looked at don't require input to heat, and will use up their charge as required to maintain the set temp. All the Redodo work that way, and the LiTime I've looked at. Here is the Redodo self heating, they are ACTUALLY self-heating, not "charger input heating":


Redodo 12V 100Ah LiFePO4 battery heater is equipped with 100W dual heating pads. This self-heating function automatically activates when the temperature of battery drops below 41°F (5°C). Once the temperature hits 50°F (10°C), heating stops, and the charing to the battery resumes normally. This revolutionary technology ensures effortless charging in cold environments.

Yah the basic requirements everyone I know with a truck camper uses are: LFP inside, in a well insulated box, stays heated overnight above 0C. A lot of folks use a reptile matt or floor heating pads to wrap battery, inside of an insulated case. They all still need to be self heated inside your camper, unless you're somehow heating camper constantly. Most folks I know actually have a self heated battery to ensure they can fire up a diesel heater after driving to camp in the cold.

It sounds like you are assuming a nice homey heated trailer setup, while I am thinking of overlanding and pickup truck camping, cold until you set up camp.

The insulation needed isn't that bulky for a single 100Ah LFP, which is all you need to bootstrap your system to start heating. Another option that I have used is a small 12V AGM that allows me to get diesel heater started, then I pipe the hot air around my LFPs as needed. Most LFP will discharge down to -20C or -4F, so you don't have to keep them that warm to draw on them to get a heater going. However, if you get below that and the BMS shuts off discharge, most folks I know report it doesn't turn back on until above 0C.

Just some more info for folks.

 

[crazysccrmd]

Ahh yah, typo, 0C
Renogy batteries, that explains it... what a poor design choice they made there.

Most self heated battery don't require input to heat, and will use up their charge as required to maintain the set temp. All the Redodo work that way, and the LiTime I've looked at.

I saw that choice as a benefit actually. While they took longer to begin charging the next day I didn’t lose up to 600wh (half an 100ah battery) overnight keeping the battery warm for charging when I wasn’t trying to charge anyway (no sun).

 

[Dave in AZ]

I saw that choice as a benefit actually. While they took longer to begin charging the next day I didn’t lose up to 600wh (half an 100ah battery) overnight keeping the battery warm for charging when I wasn’t trying to charge anyway (no sun).

Gotcha. Everyone always has different needs we forget about that don't match ours I just want to keep battery above -20C, so I can get diesel heater started when needed... then allll my heat issues are gone. 10 min after firing up my heater, I could solar charge if desired, but I absolutely want to spend battery power on ensuring my heater setup always works.

 

[Martinjmpr]

As far as relocating the batteries goes, that is in the future, but in the meantime we are less than 4 weeks from our big trip to the Southeast and the Lithium batteries have to be in place before that so as of now the plan is to keep them on the trailer tongue. While I expect sub-freezing temps I don't expect anything lower than probably the mid- to high 20's. And even that will probably only be at the beginning and end of our trip when we are close to Colorado. I expect that when we're down in Florida the temps will stay above freezing most of the time.

So here's another option: I'm looking at replacing the cheap battery box on the tongue (which currently has 2 x 12v Group 24 FLA batteries) with something like this:



There will likely be enough extra room in the box that I could put in some insulation. Do you think that would keep the batteries sufficiently warm that they wouldn't get damaged by cold weather? Once the trip is over and we're back home I have the option of taking the batteries inside the garage.

 

[rruff]

I saw that choice as a benefit actually. While they took longer to begin charging the next day I didn’t lose up to 600wh (half an 100ah battery) overnight keeping the battery warm for charging when I wasn’t trying to charge anyway (no sun).

Sorry, I went back and read more... and I agree with you! It's wasteful to keep the batteries warm when you don't need to. I'd definitely prefer batteries that only heat themselves up in the morning when you are trying to charge. The amount of energy that takes will always be less than it took to keep them warm overnight.

 

[pcstockton]

Wind chill does not affect the actual temperature. That is a human "feeling" thing only.

 

[crazysccrmd]

You're right. Apologies to the OP, my post wasn't helpful.

It's just that I think the insides of that steel box will lose heat faster if it is exposed to wind. Wind chill was my bad example. The OP need not worry of anything that extreme.

At least that has been my experience, with water in tanks starting to freeze up - exposed vs sheltered. But that might have been my bad luck.

Wind will cause whatever it is to lose heat faster than without wind so the time to cool will be faster and the time to heat will be longer. It’s still a valid concern.

 

[pcstockton]

Wind will cause whatever it is to lose heat faster than without wind so the time to cool will be faster and the time to heat will be longer. It’s still a valid concern.

Well wind will replace warmer air with colder air, but it will not change the temperature. Nothing will get colder than the air temp.

 

[crazysccrmd]

Well wind will replace warmer air with colder air, but it will not change the temperature. Nothing will get colder than the air temp.

That’s basically what I said. The batteries (and their housing if applicable) will cool faster with the added convective cooling caused by the presence of wind rather than just conductive and radiated cooling in a no wind situation.

 

[pcstockton]

Sure, but something like sunshine would balance that out.