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ceengland7(at)gmail.com
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 Posted: Sun Sep 27, 2020 1:59 pm Post subject: How do you figure C-Rating of a battery? |
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On Mon, Sep 14, 2020 at 1:09 PM rparigoris <rparigor(at)hotmail.com (rparigor(at)hotmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "rparigoris" <rparigor(at)hotmail.com (rparigor(at)hotmail.com)>
Hi Bob Thank you for your review. I will post schematic when it's completed. A few points: I'm not too worried about LiFe batteries getting thermal runaway, but I am about LiPo batteries getting to a thermal runaway. You posted a link to: https://tinyurl.com/y4oulfy9 As far as LiFe batteries go, I think mfg has done a reasonable amount of homework but fact is there is potential for problems that Lead Acid does not have and they can still fail opened. Good enough for me to use. I'm not worried about soldered and crimped connection to aluminium wires, but the terminal connections can get a high resistance. Keeping connections clean and tight mitigate majority of problems, but not all. As far as keeping NiMh pack charged, using one of my AstroFlight delta peak chargers (110D or 112D), once or twice a year will give them a C/10 for ~ 15 hours to balance, then delta peak charge the rest of the times. Unless battery is very flat, peaking at 1C takes less time than a pre-flight. 1x!
a year will capacity test down to 1V per cell and fuel pump equivalent load. BTW have you ever used an AstroFlight Whatt Meter (Whatt is correctly spelled)? Pretty slick meter that shows volts, amps and watt hours. Pricey though, here's an alternative that works pretty good: https://hobbyking.com/en_us/turnigy-180a-watt-meter-and-power-analyzer.html?queryID=7b349d17e0c87dff11877b2ea51342de&objectID=42854&indexName=hbk_live_magento_en_us_products Ron P |
Ron,
I may have stumbled upon your solution. I know you don't want LiPo in the cockpit (I can understand that). But if you're comfortable with LiFe for your main battery....
This:
https://www.harborfreight.com/lithium-ion-jump-starter-and-power-pack-62749.html?_br_psugg_q=jump+starter
At 1st glance, I was sure that it was LiPo. There's nothing in the HF ad that tells us anything different. But I just saw a video that shows it's actually a LiFePO4 battery.
https://www.youtube.com/watch?v=EbIQhskJho0&t=636s
The video shows both the label on the back of the case and the label on the battery module itself, inside the case. Now, I'm not defending the 'installation technique' he used, but the video does show what you'd be buying. You can see the case at around 3:30 in the video.
It should easily serve the dual requirements of running the fuel pump alone, or supplying an emergency jump start if you're off-airport somewhere. I'd find $85 hard to argue with....
Charlie
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rparigoris
Joined: 24 Nov 2009
Posts: 780
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| Posted: Mon Sep 28, 2020 9:13 am Post subject: Re: How do you figure C-Rating of a battery? |
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Hi Charlie Thank you for thinking of me! For back up I need something small to fit in headrest. The HF unit is too big and too heavy.
FWIT here's my take:
Harbor Freight in my experience has been less than truthful when it comes to specs and quality / reliability is an issue. I was working on a project a while back and they offered a 18aH jump start pack. It had a battery that was marked 18aH. It was a 12aH battery in a 18aH case! We took out the supplied chargers and I had a pile of them for a while. After 25 uses failure rate was 10 or 15%. Just awful. Since we took apart hundreds of units, workmanship was also awful.
Northern tools isn't any better.
For another project I needed 100 amps for a short time. I purchased from Northern Tools one of their 4,000 amp jump packs. At room temp it would put out 40 amps for 3 seconds. If it was cold out probably only 20 or 25 amps.:https://www.northerntool.com/shop/tools/product_200676383_200676383
Their# is 216-464-8131
Their 4,000 amp unit can put out ~ 40 amps for 3 seconds at minimum of 10.9 volts, after 15 seconds down to ~35 amps and if it were cold probably 20 or 25 amps.
The battery is only 8aH. (I didn't test capacity but question that as well).
Ron P.
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ceengland7(at)gmail.com
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| Posted: Mon Sep 28, 2020 10:09 am Post subject: How do you figure C-Rating of a battery? |
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On 9/28/2020 12:13 PM, rparigoris wrote:
| Quote: |
Hi Charlie Thank you for thinking of me! For back up I need something small to fit in headrest. The HF unit is too big and too heavy.
FWIT here's my take:
Harbor Freight in my experience has been less than truthful when it comes to specs and quality / reliability is an issue. I was working on a project a while back and they offered a 18aH jump start pack. It had a battery that was marked 18aH. It was a 12aH battery in a 18aH case! We took out the supplied chargers and I had a pile of them for a while. After 25 uses failure rate was 10 or 15%. Just awful. Since we took apart hundreds of units, workmanship was also awful.
Northern tools isn't any better.
For another project I needed 100 amps for a short time. I purchased from Northern Tools one of their 4,000 amp jump packs. At room temp it would put out 40 amps for 3 seconds. If it was cold out probably only 20 or 25 amps.:https://www.northerntool.com/shop/tools/product_200676383_200676383
Their# is 216-464-8131
Their 4,000 amp unit can put out ~ 40 amps for 3 seconds at minimum of 10.9 volts, after 15 seconds down to ~35 amps and if it were cold probably 20 or 25 amps.
The battery is only 8aH. (I didn't test capacity but question that as well).
Ron P.
Yeah; if you watched the entire video, he shows the 2,800mAH battery in
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the 12,000mAH case. Unfortunately, finding truth in marketing,
especially while discussing starting batteries, is a fool's quest.
Having said that, can you really fit the same power *and capacity* in
the same space, with nimh batteries? The battery itself looks to be less
than a third the volume of the case.
--
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rparigoris
Joined: 24 Nov 2009
Posts: 780
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| Posted: Mon Sep 28, 2020 10:35 am Post subject: Re: How do you figure C-Rating of a battery? |
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Hi Charlie I already have my headrest fabricated and wired. If I were to do it again I would do things differently. Energy density of LiFe batteries is better than that of NiMh. My NiMh pack fits like a glove. You can see the cutout in the aluminium plate:
http://www.europaowners.org/main.php?g2_itemId=27332
My requirement if I were to switch from NiMh to something else is to have ability for battery and BMS to fit in existing space.:
http://www.europaowners.org/main.php?g2_itemId=30608
Capacity of NiMh is less than the HF jump pack (according to Mfg. specs.), but size and weight is a lot less. NiMh pack will weigh under 2lbs. Original old cells were rated for 2.2aH which would accomplish the task, newest cells are rated for 5.0aH.
Ron P.
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ceengland7(at)gmail.com
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| Posted: Mon Sep 28, 2020 11:01 am Post subject: How do you figure C-Rating of a battery? |
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On Mon, Sep 28, 2020 at 1:46 PM rparigoris <rparigor(at)hotmail.com (rparigor(at)hotmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "rparigoris" <rparigor(at)hotmail.com (rparigor(at)hotmail.com)>
Hi Charlie I already have my headrest fabricated and wired. If I were to do it again I would do things differently. Energy density of LiFe batteries is better than that of NiMh. My NiMh pack fits like a glove. You can see the cutout in the aluminium plate:
http://www.europaowners.org/main.php?g2_itemId=27332
My requirement if I were to switch from NiMh to something else is to have ability for battery and BMS to fit in existing space.:
http://www.europaowners.org/main.php?g2_itemId=30608
Capacity of NiMh is less than the HF jump pack (according to Mfg. specs.), but size and weight is a lot less. NiMh pack will weigh under 2lbs. Original old cells were rated for 2.2aH which would accomplish the task, newest cells are rated for 5.0aH.
Ron P.
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Looks nice!
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