Re: LF/VLF: QRO in portable experiments by using LiFePo4 accus from China?

[DK7FC <selberdenken@posteo.de>]

Hello Wolfgang,

Hmm, where do you find the quote "recycled bicycle" on that site? As far as know, bicycle batteries ore usually Li-ion, not LiFePo4.
They write "Vida útil: más de 2000 ciclos". This is not very precise. Usually it means that the battery has a remaining capacity of 85% after 2000 cycles of 80% DoD. If the remaining capacity would actually be 40 Ah only, the cells would be extremely old. I would rather expect that "> 40 Ah" means just a search category.
Am i naive? :-)
Anyway, the offer is so cheap, i'm going to order one and test it in a VLF experiment, then we know! And if it has 100 Ah actually, then i'll buy 3 of these 60V/60Ah versions ;-)

73, Stefan


Am 19.03.2019 08:54, schrieb Wolfgang Büscher:

Hi Stefan,

As I understand the offer from your last link, they sell "recycled bicycle" batteries (?? - with 12 volts - ??) that once had 100 Ah when they were, with a remaining capacity of 40 Ah (as shown in one of the ads as "item condition") for use as solar power buffer, where the degraded performance doesn't matter. But I wouldn't bet on the internal cell resistance, i.e. voltage drop under heavy load...

73,
  Wolf .

On 18.03.2019 17:20, DK7FC wrote:

VLF,

After a few months of using my 12V/120Ah LiFePo4 accu (https://www.robur-akku.de/p/lifepo4-akku-12-volt-120-ah) i am really happy with the performance!

During an experiment at the ground loop i'm tracking the antenna current, see an example in the attachment. Since the feed point resistance is constant, the antenna current is proportional to the accu discharge current and also to the voltage (Power supply running in fully duty cycle, i.e. not regulated). As you can see the experiment took 2.5 hours. The accu has a display (second attachment) showing the state of discharge. At the beginning of the experiment, the accu was charged to 98%, at the end it was at 18%. As you see in the graph, the current and voltage dropped by just 1.6 % after a 50% discharge and by 12 % at the end of the transmission. These are outstanding results!

Well, the distributor is German but the accu cells are from China anyway. So why not buying in China directly?
There is an online distributor which makes offers that are hard to belive!
For example: https://www.dhgate.com/product/12-v-100ah-lifepo4-battery-for-solar/439384307.html#ctabBox  | 1 kWh/50$
or even:
https://www.dhgate.com/product/60-v-60ah-lifepo4-60-v-60ah-lifepo4-de-litio/445395613.html#s1-9-1b;searl  | 1 kWh/38.3$

How is this possible? Is it just 'fake'? I'm going to risk to buy one. No risk, no fun, as someone recently said.

73, Stefan