R-A
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batterry powered Pi in hot areas

Thu Sep 20, 2018 10:32 am

Hi,

I want to install a Raspberry Pi in a hot location (ambient temperature can reach 50-55 degrees celsius) and have a form of backup, for at least 3 hours. Lithium would be the way to go, but I don't trust them in the heat.

Any other suggestions?
I'm using a Raspberry Pi 3 Model B with 7" LCD Touch screen and Mini USB Wireless Keyboard

Paul Hutch
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Location: Blackstone River Valley, MA, USA

Re: batterry powered Pi in hot areas

Thu Sep 20, 2018 7:22 pm

AFAIK there are no standard battery types that can be charged above about 45°C. NiMH, NiCad and LiPO all can be discharged at up to 60°C and there are some high temp NiMH & NiCad good for up to 70°C.

If I was looking to solve this I think I'd probably just make sure the battery never gets charges when the temperature is above 40°C.

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Joel_Mckay
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Re: batterry powered Pi in hot areas

Fri Sep 21, 2018 7:57 am

The safe operating range for the different LiIon/LiPol cells is usually 4'C to 52'C.
Using or changing outside this zone is extremely unwise, as lipol are also exothermic during discharge.

Some sites regurgitate manufacturer specified limits as the range limits, but decent charge managers will fault if you try to exceed the SOA:
https://batteryuniversity.com/index.php ... mperatures
(you would never want to leave a Li cell cooking at 70+'C as they claim on some pages)

In general for Li cells:
below SOA temperatures cause capacity degradation, reduces discharge current limit, and charging can cause catastrophic failure.
above SOA temperatures cause capacity degradation, increase discharge current limit, and charging can cause catastrophic failure.

SLA glass pack pb batteries are #1 for standby systems, as these can:
1. Be constantly trickle changed (for a 12v pack at 25'C, that would be 13.4v at 10% Ah rating to prevent H2 gas venting.)
2. Will survive very low temperatures if fully charged (your electronics will fail before the battery)
3. There are temperature adjusted smart chargers for pb packs (and gel cells). In general some brands can do 64'C with some capacity loss, but their current output limit actually increases.
4. the cells can take abuse (think about the loads required to start a car), and most don't require smart chargers or fuel-chips to manage the pack
5. they usually fail "open" as they tend to boil off electrolyte (or swell if a gel cell), and can simply be checked with a volt meter
6. they are cheap for their capacity, and can be cycled for years if you never discharge below 11.2v on a 12v pack.

If your project doesn't care about weight, power density, or vertical mounting restrictions....
than SLA packs are the best value for capacity (gel cells are #2 as they only last a few years).

I would recommend splitting your project into two metal enclosures, and still use a SLA setup.
(we have some tested packs from 2006 still in operation today in 2018.)

Best of luck,
J

R-A
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Re: batterry powered Pi in hot areas

Fri Sep 28, 2018 7:20 am

Joel_Mckay wrote:
Fri Sep 21, 2018 7:57 am
The safe operating range for the different LiIon/LiPol cells is usually 4'C to 52'C.
Using or changing outside this zone is extremely unwise, as lipol are also exothermic during discharge.

Some sites regurgitate manufacturer specified limits as the range limits, but decent charge managers will fault if you try to exceed the SOA:
https://batteryuniversity.com/index.php ... mperatures
(you would never want to leave a Li cell cooking at 70+'C as they claim on some pages)

In general for Li cells:
below SOA temperatures cause capacity degradation, reduces discharge current limit, and charging can cause catastrophic failure.
above SOA temperatures cause capacity degradation, increase discharge current limit, and charging can cause catastrophic failure.

SLA glass pack pb batteries are #1 for standby systems, as these can:
1. Be constantly trickle changed (for a 12v pack at 25'C, that would be 13.4v at 10% Ah rating to prevent H2 gas venting.)
2. Will survive very low temperatures if fully charged (your electronics will fail before the battery)
3. There are temperature adjusted smart chargers for pb packs (and gel cells). In general some brands can do 64'C with some capacity loss, but their current output limit actually increases.
4. the cells can take abuse (think about the loads required to start a car), and most don't require smart chargers or fuel-chips to manage the pack
5. they usually fail "open" as they tend to boil off electrolyte (or swell if a gel cell), and can simply be checked with a volt meter
6. they are cheap for their capacity, and can be cycled for years if you never discharge below 11.2v on a 12v pack.

If your project doesn't care about weight, power density, or vertical mounting restrictions....
than SLA packs are the best value for capacity (gel cells are #2 as they only last a few years).

I would recommend splitting your project into two metal enclosures, and still use a SLA setup.
(we have some tested packs from 2006 still in operation today in 2018.)

Best of luck,
J
Thanx for your input.

Do you get small enough SLA batteries for a Raspberry Pi? I don't need 12V/7A capacity, as this is the smallest I can see.
I'm using a Raspberry Pi 3 Model B with 7" LCD Touch screen and Mini USB Wireless Keyboard

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Joel_Mckay
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Re: batterry powered Pi in hot areas

Fri Sep 28, 2018 7:50 am

R-A wrote:
Fri Sep 28, 2018 7:20 am
Do you get small enough SLA batteries for a Raspberry Pi? I don't need 12V/7A capacity, as this is the smallest I can see.
Spill-proof Absorbed Glass Mat (AGM) type of SLA/VRLA 12v batteries come in every capacity, but minimally a 2.3 Ah or larger battery should be used.
The shipping cost is usually why you want to find a local retail source like Walmart, digi-key, or Amazon prime.

You may also see popular alarm system replacement batteries will have higher capacity, and actually lower cost than most lower-capacity packs.

R-A
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Re: batterry powered Pi in hot areas

Fri Sep 28, 2018 9:06 am

Joel_Mckay wrote:
Fri Sep 28, 2018 7:50 am
R-A wrote:
Fri Sep 28, 2018 7:20 am
Do you get small enough SLA batteries for a Raspberry Pi? I don't need 12V/7A capacity, as this is the smallest I can see.
Spill-proof Absorbed Glass Mat (AGM) type of SLA/VRLA 12v batteries come in every capacity, but minimally a 2.3 Ah or larger battery should be used.
The shipping cost is usually why you want to find a local retail source like Walmart, digi-key, or Amazon prime.

You may also see popular alarm system replacement batteries will have higher capacity, and actually lower cost than most lower-capacity packs.
Hi,

No, I meant, does one get a 5V SLA battery? Those 12V batteries are rather big and I don't have enough space to fit it.
I'm using a Raspberry Pi 3 Model B with 7" LCD Touch screen and Mini USB Wireless Keyboard

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Joel_Mckay
Posts: 177
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Re: batterry powered Pi in hot areas

Fri Sep 28, 2018 10:08 am

Battery cell voltages change under discharge, so one should use a USB 5A 5v DC-to-DC buck-converter like the XL4015 modules on e-bay.
Note these often claim 5A output, but it is usually more like 3A at best due to the components used (unless you plan to fry eggs).

The voltage on the regulator module input can vary from 24vDC to 7vDC, often achieves >85% efficient step-down power conversion, and outputs a regulated 5vDC to a USB port. If your power density requires something smaller, you could probably get away with a 1.2 Ah 12vDC battery with a reasonably efficient buck-converter. This works as it could still safely provide 1.8A at 5vDC for a Pi3B+, but only because it would draw around 0.9A from the 12V battery due to the power conversion efficiency.

In general, you never want to discharge a pack in less than 1 hour with high loads, as it could potentially off-gas/explode or reduce battery life. Thus, the power output demand sets the physical size options due to the power-density offered by the battery chemistry. i.e. This is about as small as it should get with an SLA... ;-)

As I don't know the parameters of your project, it is impossible for me to comment further.
> +60'C will certainly limit your options... ;-)

Best of luck,
~J~

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