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Apr 16, 2021, 07:19 AM
Tragic case
davidleitch's Avatar
Quote:
Originally Posted by ptxman
We used battery heater boxes (and post race cooler tubes! in F5D back in the day. I can probably dig up some pics from the archives. A good way of building a controllable toaster is using power resistors lined up on either side of the box. I fed it with same 12V supplying the charger bus bar. A cheapo digital thermometer with probe. And either a control potentiometer or just switch a certain number of resistors on, low/high/medium. The box itself can be quite unsophisticated. I just used a simple wood construction sized to the packs. Avoid metal foil type insulation because all it takes is a inadvertent contact to mains or balancing plug & you have a short & fire. You might find a suitable heating blanket but most of the ones I looed at were more trouble then they are worth given low wattage or mismatched input voltage etc. I would not incorporate a heater into a charge box personally, but these packs are quite small and 'less' dangerous.

I'm assuming the intent is to lower internal resistance & therefore increase voltage? The thing is, batteries IR is getting so good these days as evidenced by high C-ratings (if you believe the sticker). I'm kind of curious as to why? I can see pre-heat on a frosty 0-degC day, but things start changing as soon as you button up the canopy. The pack is cooling off even as you walk to the flight line to start. In flight is being cooled by ambient air & simultaneously heated by its own IR, the relative rates depending on a bunch of variables that may well vary flight to flight. Thats why you can get puffed packs on hot days. And unlike racing, F5J climb is all over with in max 30 seconds assuming a full climb duration at max power, but typically less. Just some random thoughts FWIW.
According to a presentation on RC Groups, titled "Lithium Polymer Battery Technology - An introduction with special consideration RC model lithium batteries" by Frank Siegert which is about 78 slides long and I found a very good read and reference although it only reflected technology as of 2019. it goes into anode and cathode chemistries, dendrites and all the stuff that an electricity analyst like me reads about in relation to electric cars. Anyhow back on topic "Cell performance is highly affected by temperature, performance numbers of a of a cell are valid only for temps at or above 30 celsius . C rates drop dramatically below 20 celsius bot for discharge and especially charge rates". HEAT THE CELL to 30 CELSIUS before use. Equally at high temperatures > 55 Celsius degenerate effects set in and cell ageing is accelerated.

And I would add performance is more predictable if you always warm the cells to the same temperature before flying.

F5J batteries are almost trivially cheap so I guess it doesn't matter than much but if you want to maximise their value and performance you need to manage them.

Long life tips:
Store cool, dry and empty (less than 20 celsius)
Never over charge
Never over discharge
Optimal working temperature range 30 celsius to 40 celsius
Only keep at working temperature during use as short as time as possible (good luck with that in australian summer)
Cycle lifetime doubles if you only charge to 4.1 volts
Cycle lifetime doubles at less than 70% depth of discharge

most advice is well known but I repeat it anyway.
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Apr 16, 2021, 08:32 AM
Subliminal User
Jubz's Avatar
Quote:
Originally Posted by dutchsoarer
This bag has all the components you need besides a little spare time:
https://hobbyking.com/nl_nl/catalogs...=lipo%20warmer

I made this of it. Cd-case, isolation, a cheap bec and ready.

Small enough to put everything (transmitter, tools) in just one (stanley) toolbox when I go out flying.
Main battery is a 4S 10Ah lifepo4, always ready charged.
Less is more, no risk to forget something (besides parts of the plane ;-) )

Jan
Very nice. Do you have a link to source the CD case?
Apr 16, 2021, 11:20 AM
Registered User
Quote:
Originally Posted by Jubz
Very nice. Do you have a link to source the CD case?
Well, the brand is called leitz. The product however is not produced anymore , bought mine about 5 years ago for 3 euro in a local junk shop.

The point I have tried to make is that one of the big plusses of F5J - for me - is that you don't have to lug around so much junk. Put all the things you need for flying in just 1 (small) toolbox.

Jan
Last edited by dutchsoarer; Apr 16, 2021 at 11:30 AM.
Apr 16, 2021, 06:16 PM
Registered User
Thread OP
Hereís a picture of whatís going inside my box. Iím putting this aside for now but I hope it helps folks with ideas. Iím not going to charge through the BMS but you could.
Apr 16, 2021, 06:57 PM
Tragic case
davidleitch's Avatar
Good photo. I like to see the kit parts like that.
Apr 17, 2021, 11:15 AM
Registered User
Thread OP

Just thinking out loud


So the SLA battery I ordered for the charging box is a few pounds. From a design stand point that means it needs to be clamped down securely in the case. In my mind the clamps for the battery will also act as supports for the deck. The deck will need supports since the case I purchased from Amazon does not have supports molded in. If you are familiar with Nanuk cases or even the Progressiverc cases, deck supports and lid supports are molded in. If you wanted to make a deck you could just use 1/4 plywood and screw it to these posts. The deck design ends up being pretty simple.

1. Mount for m6d
2. Posts for 12v out and to charge the SLA
3. DPDT switch for 12V on / off / external battery
4. Three XT60 connectors panel mounted for port 1, port 2, and external battery
5. Two 6s balance port extensions
6. Some holes for ventilation. I am not adding external fans.

I decided for safety I would add a 30A push button breaker. I used these in a few race cars and they are okay. You can only reset them. There are DC marine breakers that you can throw on and off. These are actually better but they are $15. I will probably use this in my own charger box.

Oh by the way I will more than likely donate this box to raise funds for Team USA F5J. Look for that later.
Apr 18, 2021, 05:40 AM
Registered User
Thread OP
First print was pretty close. I designed a lip so the deck just sits inside without support and it works great. You can see how much larger the box for the gel battery is compared to the case for the lithium batteries.
Apr 24, 2021, 07:13 PM
Registered User
Thread OP

Teaser


Ver. 1 is done! If you are a maker often times this is the point where you stop. But part of the joy of sharing your makes is evolving and honing your design so you can feel satisfied that others enjoy it as much as you. A few more hours and this should come out really nicely. I decided to use 2 machine screws to secure the deck. Gives it a more robust feel.
Apr 24, 2021, 07:15 PM
Tragic case
davidleitch's Avatar
Cool digger. Looks smooth
Apr 26, 2021, 09:11 AM
Registered User
Thread OP

Final build list and assembly instructions


I finally got the design where I think it needs to be and the final print is running now. I'm using a PET but a PLA+ should work just as well. Normal PLAs tend to shrink over time if exposed to moderate heat cycling. Also considering we leave these outside in the sun a normal PLA with it's lower glass temperature may warp easily. Printing the deck in a light color like white or natural should help. I wish these cheap cases came in light color plastics but typically they do not so the case itself will draw and hold more thermal energy.

One thing of note, thanks to the crazy times we live in today, the price of the parts has increased about 5-10% in the last week. For example the case increased $6 which is 20%.

Toolkitrc M6D - $59
https://www.progressiverc.com/produc...8055c1b1&_ss=r

The case on amazon, yes the price increased - $36:
https://www.amazon.com/dp/B07SL3CS3Y...roduct_details

12V SLA, yes the price increased too !!! -$40
https://www.amazon.com/dp/B00KC39BE6...roduct_details

The ON/OFF/ON switch - $5
https://www.amazon.com/dp/B085ZD3YM7...roduct_details

Panel mount XT60, same story the price increased - $13
https://www.amazon.com/dp/B07GQVHB3V...roduct_details

4mm banana plugs - $13
https://www.amazon.com/dp/B077ZLG2J4...roduct_details

2 6s balance extensions

4 battery side XT60 connectors

1 female XT60 connector

3/4"-1" 1/4-20 button heads screws

1 1/2" - 2" 1/4-20 machine head screws

12-14 gauge wire, about 2 feet

That's a total component price list of about $200 not counting some kind of charger for your SLA battery. If you have an external power supply you can charge the SLA with the M6D. Considering it is a dual charger of decent wattage, I would recommend an external power supply so you can use this as a bench charger.
Apr 28, 2021, 02:40 PM
Registered User
Thread OP
I’ll keep updating the above post but since it’s 90 degrees today here in NJ I decided to tests the deck in heat. PET warps slightly. Going to try another filament for the final version.


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