Author Topic: 12V DC UPS  (Read 5336 times)

0 Members and 1 Guest are viewing this topic.

Offline Alex EisenhutTopic starter

  • Super Contributor
  • ***
  • Posts: 3550
  • Country: ca
  • Place text here.
12V DC UPS
« on: July 22, 2022, 05:09:11 pm »
So the battery died on my very small home UPS that I used for the modem and router. I used it to give me maybe 5-10 minutes of connectivity to save stuff in case of power failure.

The thought occurred that it's quite silly to have this DC->chop to AC->wall wart chain just to have 12V for the modem.

So there are 12V mini-UPS things on Alix... Any good? Experiences? Thoughts?

It's the same price as trying to track down a new 12V gel cell for my UPS, so...

 :-//

https://www.aliexpress.com/item/1005004107179526.html
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 

Offline NiHaoMike

  • Super Contributor
  • ***
  • Posts: 9321
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: 12V DC UPS
« Reply #1 on: July 23, 2022, 12:33:46 am »
Just get a 3S pack with BMS and connect it to the 12V bus using a Schottky diode and resistor, or directly if the DC supply is current limited to within the charge current limit of the battery. It turns out that 12V yields 4V/cell for 3S, which is OK to leave connected indefinitely.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 
The following users thanked this post: SeanB

Offline Ed.Kloonk

  • Super Contributor
  • ***
  • Posts: 4000
  • Country: au
  • Cat video aficionado
Re: 12V DC UPS
« Reply #2 on: July 23, 2022, 01:17:17 am »
Under the mountain of paperwork on my desk there should be an envelope on which I've drafted a plan to build usb powerbank with power pass through and a 5v->12v boost converter module for the router/firewall in the garage in case of power failure.

I don't doubt it would work, I just haven't got around to doing it.


Cos I'm so lazy, I ended up just buying a 7Ah gel cell and put it in this:
https://www.altronics.com.au/p/m8561-12v-dc-ups-battery-backup-power-supply/

That was about 7 years ago. Still works OK as of two nights ago when our power got knocked out by some trees.
iratus parum formica
 

Offline Alex EisenhutTopic starter

  • Super Contributor
  • ***
  • Posts: 3550
  • Country: ca
  • Place text here.
Re: 12V DC UPS
« Reply #3 on: July 23, 2022, 05:06:30 am »
For the price of the Alix thing I'm not motivated in the slightest to kludge something together. I just had this feeling that the clunky, chunky, and heavy lead-acid inverter UPSs, with their tiny battery life and at the same time six or eight AC outlets for 150$ CDN, just make no sense. I still can't really believe they're actively sold.

So I ordered the Alix thing.  8)
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 
The following users thanked this post: Ed.Kloonk

Offline Ed.Kloonk

  • Super Contributor
  • ***
  • Posts: 4000
  • Country: au
  • Cat video aficionado
Re: 12V DC UPS
« Reply #4 on: July 23, 2022, 05:22:53 am »
For the price of the Alix thing I'm not motivated in the slightest to kludge something together. I just had this feeling that the clunky, chunky, and heavy lead-acid inverter UPSs, with their tiny battery life and at the same time six or eight AC outlets for 150$ CDN, just make no sense. I still can't really believe they're actively sold.

WRT the lead-acid consumer UPS, not sure about your locale but here there was a push some years ago among the office supply big stores to shove these things down everyone's throats. And yeah, you're right. They're shit. I have a fine collection of dead soldiers.

Quote
So I ordered the Alix thing.  8)

I like the wide input voltage range. Again, locale. I'd need to be watching the package heat during summer time.
iratus parum formica
 

Offline Emo

  • Regular Contributor
  • *
  • Posts: 133
  • Country: nl
Re: 12V DC UPS
« Reply #5 on: July 23, 2022, 07:53:44 am »
 
The following users thanked this post: Miyuki

Offline Miyuki

  • Frequent Contributor
  • **
  • Posts: 908
  • Country: cz
    • Me on youtube
Re: 12V DC UPS
« Reply #6 on: July 25, 2022, 05:00:25 am »
I use this DIY solution and it works great, offers days of backup when powering just a network infrastructure

It is a Mean Well power supply with a backup feature, so it manages the battery
24V system with two 12Ah lead acids, they had the best price/capacity ratio
Added 12V step-down converter and 48V boost

The main part of the network are Miktorik based routers/AP and they use 24V PoE, which is why choose the 24V system
I need the 48V for the DSL modem as it uses a TP-Link PoE extractor and this need 802.3af voltage levels
And have 12V output for things like NAS

It is cheap and robust
I wanted to add some more features, like measuring, more protection and so, but maybe sometimes in the future
It just works  ::)
 

Offline Geoff-AU

  • Regular Contributor
  • *
  • Posts: 241
  • Country: au
Re: 12V DC UPS
« Reply #7 on: July 25, 2022, 05:34:00 am »
For the price of the Alix thing I'm not motivated in the slightest to kludge something together.

The downside being, that kind of gear is designed without caring about creepage, clearance, or any safety measures really.  If it doesn't kill people on the day of sale, it's good enough.  Never mind if it catches fire next week.

I use this DIY solution and it works great, offers days of backup when powering just a network infrastructure

Hm.  "Strain relief" (knotted mains cord) that leads to a gaping hole larger than the knot, exposed high-current battery wires, masking tape on the battery terminals..  is that Meanwell even secured or is it just sitting on the shelf?  Good God, man, I think that's even more dangerous than the Aliexpress product.  Have you no shame?
 

Offline Miyuki

  • Frequent Contributor
  • **
  • Posts: 908
  • Country: cz
    • Me on youtube
Re: 12V DC UPS
« Reply #8 on: July 25, 2022, 05:49:12 am »
I use this DIY solution and it works great, offers days of backup when powering just a network infrastructure

Hm.  "Strain relief" (knotted mains cord) that leads to a gaping hole larger than the knot, exposed high-current battery wires, masking tape on the battery terminals..  is that Meanwell even secured or is it just sitting on the shelf?  Good God, man, I think that's even more dangerous than the Aliexpress product.  Have you no shame?
A little shame  :-[
It is considered a "test" and "not finished"
Normally it is closed and sits in the corner
The power supply is secured in place
Exposed wires are not directly from batteries, they go from the Meanwell and it is fused, so not as dangerous as it looks
But I agree it is not a example how it shall be used
 

Offline beanflying

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: au
  • Toys so very many Toys.
Re: 12V DC UPS
« Reply #9 on: July 25, 2022, 05:58:44 am »
Just get a 3S pack with BMS and connect it to the 12V bus using a Schottky diode and resistor, or directly if the DC supply is current limited to within the charge current limit of the battery. It turns out that 12V yields 4V/cell for 3S, which is OK to leave connected indefinitely.

Number of times you have FALSELY posted about BMS circuitry and charging Lithium cells is now +1. Please go learn once and for all how Lithium batteries are charged and a tip that is NOT USING A BMS.

STOP IT !

Lithium Batteries are a multi step charge process so that is neither just constant current or using a Diode on a random power supply as some sort of  :bullshit: limiter.
« Last Edit: July 25, 2022, 06:00:32 am by beanflying »
Coffee, Food, R/C and electronics nerd in no particular order. Also CNC wannabe, 3D printer and Laser Cutter Junkie and just don't mention my TEA addiction....
 
The following users thanked this post: tooki

Offline tom66

  • Super Contributor
  • ***
  • Posts: 7334
  • Country: gb
  • Electronics Hobbyist & FPGA/Embedded Systems EE
Re: 12V DC UPS
« Reply #10 on: July 25, 2022, 07:04:12 am »
I did something similar for our CCTV DVR.  Modded the power supply to output 13.2V instead of 12V (within the +10% range for the ATX hard drive) which kept a small lead acid battery semi-charged.  It's sufficient to keep the system going for about half an hour in a power cut, and it backpowers the cameras too through the 12V socket. 

The only problem I've found is the hard disk is the first thing to cut off, but if the power comes back before the DVR dies, it takes a while before the DVR detects the HDD again.  I need to add a 'UVLO' circuit to properly reset things.
 

Offline NiHaoMike

  • Super Contributor
  • ***
  • Posts: 9321
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: 12V DC UPS
« Reply #11 on: July 25, 2022, 12:46:31 pm »
Number of times you have FALSELY posted about BMS circuitry and charging Lithium cells is now +1. Please go learn once and for all how Lithium batteries are charged and a tip that is NOT USING A BMS.

STOP IT !

Lithium Batteries are a multi step charge process so that is neither just constant current or using a Diode on a random power supply as some sort of  :bullshit: limiter.
https://www.electronicsweekly.com/market-sectors/power/float-charging-lithium-ion-cells-2006-02/
Quote
In float charging, current entry beyond full charge is prevented by choosing a charge voltage less than or equal to the voltage naturally produced by the cell at full charge – which depends on the cell’s exact electrochemistry and temperature.

“It is all related to battery voltage,” says Robin Cloke, UK MD of GP Batteries. As a general rule of thumb, “if you choose around 4.0V it is fairly safe for the cell”.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline beanflying

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: au
  • Toys so very many Toys.
Re: 12V DC UPS
« Reply #12 on: July 25, 2022, 01:13:44 pm »
Number of times you have FALSELY posted about BMS circuitry and charging Lithium cells is now +1. Please go learn once and for all how Lithium batteries are charged and a tip that is NOT USING A BMS.

STOP IT !

Lithium Batteries are a multi step charge process so that is neither just constant current or using a Diode on a random power supply as some sort of  :bullshit: limiter.
https://www.electronicsweekly.com/market-sectors/power/float-charging-lithium-ion-cells-2006-02/
Quote
In float charging, current entry beyond full charge is prevented by choosing a charge voltage less than or equal to the voltage naturally produced by the cell at full charge – which depends on the cell’s exact electrochemistry and temperature.

“It is all related to battery voltage,” says Robin Cloke, UK MD of GP Batteries. As a general rule of thumb, “if you choose around 4.0V it is fairly safe for the cell”.

4V is 'safe' for most Lithium options BUT you do not get there by ANY METHOD in your initial post! Don't randomly Google for answers YOU WANT to suit your argument instead do some actual reading on how done safely to suit the Lithium Technology in question.

Start with understanding what a BMS board is and is not.
Coffee, Food, R/C and electronics nerd in no particular order. Also CNC wannabe, 3D printer and Laser Cutter Junkie and just don't mention my TEA addiction....
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 7334
  • Country: gb
  • Electronics Hobbyist & FPGA/Embedded Systems EE
Re: 12V DC UPS
« Reply #13 on: July 25, 2022, 01:50:38 pm »
Float charging Li-ion batteries is simply not possible:  you cannot apply a fixed 4V if the battery is at say 3.5V, the current drawn during charging will be excessive which will overheat the cell.  You need both current limiting and voltage limiting.  Now, you can modify a standard li-ion charger IC with an external comparator so that it shuts off once the cell goes over e.g. 4V,  which will create the 'effect' of float charging, but the result will be that the charger cycles on and off around that point, so not really float charging.  It will certainly extend the cell's lifespan, the rule I have heard is doubling calendar life for every 0.1V less than 4.25V.

It is NEVER permissible to charge a li-ion cell with only a resistor or simple current limiter, cell voltage will increase until the cell is destroyed,  if the current is high enough this may well result in thermal runaway.
 

Online Siwastaja

  • Super Contributor
  • ***
  • Posts: 9334
  • Country: fi
Re: 12V DC UPS
« Reply #14 on: July 25, 2022, 03:23:05 pm »
Number of times you have FALSELY posted about BMS circuitry and charging Lithium cells is now +1. Please go learn once and for all how Lithium batteries are charged
...
Lithium Batteries are a multi step charge process so that is neither just constant current or using a Diode on a random power supply as some sort of  :bullshit: limiter.

How about you dropping your attitude and go learn how lithium ion batteries are charged.

But if you can't even get the name (lithium ion; lithium batteries are a different thing) right, I guess there is very little hope for you.

I see no big issues in NiHaoMike's suggestion. Of course, he leaves out the detail what he exactly means by "BMS". But he often leaves out details to be worked on.

Clearly, you don't have any idea about the "multi-step process" you are talking about.

Also the battery does not know or care if current is limited using a resistor or something more fancy, and I think it's quite revealing you can't understand even this.

In the future, you might want to consider this: if you think someone is giving poor or dangerous advice, learn the thing first, and then properly explain what is wrong. And remember, to be able to teach others, you need to have quite solid understanding.
« Last Edit: July 25, 2022, 03:25:56 pm by Siwastaja »
 
The following users thanked this post: NiHaoMike

Online Siwastaja

  • Super Contributor
  • ***
  • Posts: 9334
  • Country: fi
Re: 12V DC UPS
« Reply #15 on: July 25, 2022, 03:32:58 pm »
Float charging Li-ion batteries is simply not possible

Of course it is, I regularly do it.

The suggestion was using a constant-voltage supply plus a current limiter resistor. This provides both current and voltage limiting.

But you need to understand Ohm's law to be able to dimension the resistor. If you need help with that, you can ask about it in the Beginners section. Thank you.

Mike's suggestion of having a BMS - practically this would be most easily satisfied by using "protected cells" with built-in single-cell protection PCB - would take care of adding another layer of security in case the upstream 12V supply fails in a way making it output a higher voltage - unlikely but possible. Resistors basically never fail short, so current limiting will be very robust. This basically just leaves the low-voltage cutoff functionality on the shoulders of the protection boards. BMS boards would also open the circuit if gross imbalance develops, but this is again unlikely. Or one can use a balancing 3S BMS.

If you use decent quality non-bullshit cells, this is one of the least risky mods one can do. But as always, there is some risk to anything. I just find it extremely funny people jump on this particular li-ion usage tip, because we see orders of magnitude worse every day on this forum and no one gives a shit.

Probably because they don't understand what they are talking about, and get fixated on some single words like "float charging", after reading from Battery University or some other BS site that "float charging a lithium ion cell is impossible".
« Last Edit: July 25, 2022, 03:35:34 pm by Siwastaja »
 
The following users thanked this post: NiHaoMike

Offline tom66

  • Super Contributor
  • ***
  • Posts: 7334
  • Country: gb
  • Electronics Hobbyist & FPGA/Embedded Systems EE
Re: 12V DC UPS
« Reply #16 on: July 25, 2022, 03:54:24 pm »
Siwastaja, what happens to your float charging circuit and the battery, if the battery runs to <2.8V and you connect it to the 4V supply with the current limiting resistor?

This is not as simple as Ohm's law: below about 2.5-2.8V, Li-ion cell current must be around C/25 or lower.  Otherwise, you risk dendritic build up in the cell in the recovery phase which can lead to future runaway.

Now what happens if the cell is totally dead (0V terminal) and you power the charger circuit up?  A good Li-ion charger circuit will not charge the cell at all in that condition.  But, your circuit will attempt to charge the cell -- and it will charge it with considerable current given the volt-drop across the resistor -- which could result in the cell releasing its magic smoke.  (Note that relying on the battery protection board to do this is not necessarily OK.  The protection boards often allow charging in this condition, just do not allow discharging.)

I don't believe you can ever build a safe Li-ion charging circuit with just a CV source and a resistor, and there is no manufacturer of Li-ion cells that will recommend it.  For other lithum rechargeable chemistries, for instance lithium manganese silicon (example Seiko ML414) then this is tolerable, but this is only because the parasitic reactions in the cell are so high as to keep the cell in a safe condition at all times.  This definitely does not apply to Li-ion cells.
« Last Edit: July 25, 2022, 03:58:02 pm by tom66 »
 

Online Siwastaja

  • Super Contributor
  • ***
  • Posts: 9334
  • Country: fi
Re: 12V DC UPS
« Reply #17 on: July 25, 2022, 05:17:35 pm »
Siwastaja, what happens to your float charging circuit and the battery, if the battery runs to <2.8V and you connect it to the 4V supply with the current limiting resistor?

That was already covered. I won't repeat it because it is futile to do so with people who lack the skill to concentrate on the text. Instead, please read, re-read, and re-re-read until understood.

It was already present in NiHaoMike's original post, which was extremely short and to the point. I just elaborated on it.

I'll give you a hint, though: a three-letter acronym was discussed.
« Last Edit: July 25, 2022, 05:20:10 pm by Siwastaja »
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 7334
  • Country: gb
  • Electronics Hobbyist & FPGA/Embedded Systems EE
Re: 12V DC UPS
« Reply #18 on: July 25, 2022, 06:23:10 pm »
Read and re-read yet I'm still baffled; if you think a BMS, which I'll assume is the acronym in question, is going to prevent the runaway condition, you are sorely mistaken.  But thank you for questioning my reading comprehension; I'll question your battery charging comprehension instead, since this is a technical discussion.

The vast vast majority of 3S packs (e.g. hobby RC packs) have no in built BMS and so the advice suggested (4V constant voltage with resistor per cell) is very dangerous for inexperienced users.  If they DO have a proper balancing BMS this may work, however it will need to be close to the protection circuitry that for example a laptop battery offers. 

You will still need to provide protection in the case of 2.8V/cell or less.  Many battery protection circuits DO NOT isolate the battery from charging currents when the battery is under-voltage; the reason for this is to allow the battery to be recovered by an appropriate charger, which is usually possible down to about 1.5-1.8V/cell with some deterioration in the capacity if the charge is replaced very slowly.  The exceptions are things like power tool batteries, because users are idiots and will try anything to recover their 100 euro battery that they left discharged, these tend to prohibit almost all zero volt charging as the terminals are too tempting to hook up to some external source.  But I can confirm that the majority of BMS circuits will not block charging below 2.8V; for instance, the BQ20z70 device used in a great deal of laptop batteries allows zero-volt charging, and it applies no special current limit in this case; neither do common single-cell Li-Ion isolators like AP9221 or the venerable DW01 which is seen in pretty much every cheap single cell protected Li-Po.   There are a few laptop batteries with pyrofuse devices like 12AH3 which can semi-permanently isolate the pack if it's gone below a certain voltage.  Again, quite rare, and usually only seen in very high volume consumer kit.

Therefore, I continue to insist that you should not recommend charging any Li-Ion battery pack with only a voltage source and resistor.  It really is very little extra cost to use a proper Li-Ion charger chip and protection circuit, and offers a significant improvement to the safety of the system.  The danger, as ever, is that advice is copied by those who have no appreciation for the danger that Li-Ion batteries pose, and then implement chargers like this thinking it's perfectly sufficient. 
 

Offline beanflying

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: au
  • Toys so very many Toys.
Re: 12V DC UPS
« Reply #19 on: July 26, 2022, 02:05:23 am »
Siwastaja, what happens to your float charging circuit and the battery, if the battery runs to <2.8V and you connect it to the 4V supply with the current limiting resistor?

That was already covered. I won't repeat it because it is futile to do so with people who lack the skill to concentrate on the text. Instead, please read, re-read, and re-re-read until understood.

It was already present in NiHaoMike's original post, which was extremely short and to the point. I just elaborated on it.

I'll give you a hint, though: a three-letter acronym was discussed.

Speaking of 'attitude' over something you chose to step into :-DD

Mike's suggestion was WRONG on multiple levels.

Your own LACK of knowledge on charging multicell Lithium packs is showing. I have been charging LiPo's for well over a decade so I have more than a little idea about multistage charging of them. Resistors, Diodes and other simplistic current limiters are also NOT the appropriate way to 'limit current' lower voltage or 'float' charge a Pack of Lithium batteries at X volts. Cells are not matched for impedance, capacity and in most cases not even from the same batch run.

A BMS is a safety cutout no more and no less is is not now and never will be an appropriate method to terminate a multicell Lithium Charge process. This LIE and a potentially dangerous one is spread all over the web and as this is an Engineering forum this needs to be stamped out here at least. Stack Exchange, Reddit and the countless YouTube videos are complete  :bullshit:

Quote
Or one can use a balancing 3S BMS

This is called a Balancing CHARGER congratulations you finally mentioned the appropriate thing to use to charge Lithium multicell packs. The only thing you added INCORRECTLY (in 95% of cases) that is not part of the charging circuit is the BMS which is a battery protection device :palm:
« Last Edit: July 26, 2022, 02:14:48 am by beanflying »
Coffee, Food, R/C and electronics nerd in no particular order. Also CNC wannabe, 3D printer and Laser Cutter Junkie and just don't mention my TEA addiction....
 
The following users thanked this post: tooki

Offline PlainName

  • Super Contributor
  • ***
  • Posts: 7508
  • Country: va
Re: 12V DC UPS
« Reply #20 on: July 26, 2022, 06:54:26 pm »
Hello :)

Just to shortcut even more angriness, perhaps I can butt in and point out:

Quote
A BMS is a safety cutout no more and no less is is not now and never will be an appropriate method to terminate a multicell Lithium Charge process.

My understanding (of the suggestion, not batteries) is that the BMS is intended to stop the cell being depleted below 2.8V (or whatever the safe minimum is). It's not intended to be part of the charging system, which is what the constant voltage and resistor is. The CV/R is thus 'safe' because the battery will be disconnected by the BMS on over-discharge, so the <2.8V and 0V situations won't arise. Maybe a small fuse just in case would round it off.

You're welcome  ^-^
 
The following users thanked this post: NiHaoMike

Offline tom66

  • Super Contributor
  • ***
  • Posts: 7334
  • Country: gb
  • Electronics Hobbyist & FPGA/Embedded Systems EE
Re: 12V DC UPS
« Reply #21 on: July 26, 2022, 07:58:20 pm »
The point is many BMS devices only provide balancing and overvoltage/overcurrent protection.  They are not smart enough to provide full protection for the cell, like adjusting the current limit at low state of charge.  That is the responsibility of the charging IC / controller.
 

Offline PlainName

  • Super Contributor
  • ***
  • Posts: 7508
  • Country: va
Re: 12V DC UPS
« Reply #22 on: July 26, 2022, 11:23:32 pm »
Maybe those would be the wrong BMS to use, then. I mean, if your design is based around a 5V zener it's a bit pointless to note that all those snazzy diodes and diacs and what have you would really suck at the job.

But I reckon I am best out of it now...
 

Offline beanflying

  • Super Contributor
  • ***
  • Posts: 7375
  • Country: au
  • Toys so very many Toys.
Re: 12V DC UPS
« Reply #23 on: July 27, 2022, 02:03:16 am »
Even the basic BMS boards typically provide over and undervolt battery protection including evilbay/AliX rubbish.

Because of the low impedance of most Lithium cells you can't charge as Constant Voltage from near flat (circa 3V) toward a 4V or better a 4.2V charged state. You need to use a controlled current source for the initial bulk charge a resistor and diode is not such a source. Toward the top for the last 10% of capacity (generally over 4V) this is where a Constant Voltage type of charge is done.

And before anyone bleats again about my use of the generic 'Lithium' rather than a specific type be that ion, polymer, Fe ..... it is for a reason not all Lithium Rechargeable Cells are the same but most share similar charge and use conditions.
Coffee, Food, R/C and electronics nerd in no particular order. Also CNC wannabe, 3D printer and Laser Cutter Junkie and just don't mention my TEA addiction....
 

Offline NiHaoMike

  • Super Contributor
  • ***
  • Posts: 9321
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: 12V DC UPS
« Reply #24 on: July 27, 2022, 02:19:47 am »
Because of the low impedance of most Lithium cells you can't charge as Constant Voltage from near flat (circa 3V) toward a 4V or better a 4.2V charged state. You need to use a controlled current source for the initial bulk charge a resistor and diode is not such a source. Toward the top for the last 10% of capacity (generally over 4V) this is where a Constant Voltage type of charge is done.
The resistor value is chosen to keep the current below the max charge rating of the battery. The current will go down as the battery charges, that's perfectly fine if fast charging is not the goal.

The 4.2V figure is to get the full rated capacity which is not desirable in this case. A lower voltage reduces the usable capacity but also reduces the degradation over time so in the long run it ends up cheaper. It's a completely different use case than for a drone where weight reduction is everything.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf