Re: Easy Service Call - Impressive Batteries

[Jim Rojas <jrojas@xxxxxxxxxxxx>]

On 8/9/2015 12:38 AM, ABLE1 wrote:
> On 8/8/2015 3:06 PM, Jim Rojas wrote:
>> On 8/8/2015 2:48 PM, ABLE1 wrote:
>>> On 8/7/2015 9:13 PM, Jim Rojas wrote:
>>>
>>>>
>>>> A few months back I started experimenting with Li-Mn batteries on my
>>>> own
>>>> security system.
>>>>
>>>> At the moment I have 2 banks of four 18650 2200ma Li-Mn batteries.
>>>> It is
>>>> roughly a 4AH setup at the moment. So far, no problems whatsoever. I
>>>> did
>>>> have to discharge the batteries down to 3 volts each so the security
>>>> system would be able to charge them up to about 13.5 volts. So far, no
>>>> problems at all. I still need to fully test backup time though. Since I
>>>> am not over stressing the batteries at 3.7-4.2v, they should last a lot
>>>> longer, and provide roughly 10 percent less of their overall rated
>>>> capacity. This is something you just can't do with SLA batteries.
>>>>
>>>> I plan to add 2 more banks to give me a total of 8AH more or less. The
>>>> nice thing about this setup is that it allows me to replace a single
>>>> bad
>>>> cell without tossing out the rest of the batteries. This is something I
>>>> always disliked about SLA batteries. Sure I can buy Li-ion or Li-Mn
>>>> battery for about $100 each, but then I have the same problem with them
>>>> being sealed.
>>>>
>>>> I wouldn't recommend doing this out in the field, but it would be nice
>>>> to see these type batteries used for security systems in the future
>>>> at a
>>>> much lower cost. I can see this battery bank lasting 6-8 years without
>>>> any real issues.
>>>>
>>>> If all works as planned, I will encase the completed battery bank in a
>>>> metal or plastic enclosure to minimize the possibility of a short
>>>> circuit.
>>>>
>>>> Jim Rojas
>>>>
>>>
>>> Hi Jim, haven't see you around these here parts for a long time.  Hope
>>> all is well in the "sunshine (among other things) state".
>>>
>>> So now you had to put new input into my brain that forced me to Google
>>> some stuff.  LiMn Lithium Manganese.  From what I have read they have
>>> high amp short life or something like that.
>>>
>>> I assume that you are using something like these.
>>> http://www.smoktek.com/Efest-18650-Hybrid-IMR-Li-Mn-Battery--2200mAh-37V-button-top_p_862.html
>>>
>>>
>>>
>>>
>>> Assuming that you are putting 3 batteries in a bank??
>>> Then you have a voltage per bank of  3 = 11.1 to 12.6vdc
>>>
>>> So what happens when you pull the AC from the panel??  How long do they
>>> stay up before a low battery happens??
>>>
>>> Interesting stuff.
>>>
>>> Thanks,
>>>
>>> Les
>>>
>>>
>>>
>>>
>>>
>>
>> Hi Les. No, I am using four 18650 batteries in series which comes to
>> around 15v. If you use 3 batteries, then you are over stressing the
>> batteries and it would last no longer than SLA batteries. So what I do
>> is drain each bank down to no less than 11 volts under a light load.
>> Then you can connect it to the alarm system. It works like a charm so
>> far.
>>
>> Jim Rojas
>>
>
> Ok, so you are tricking the panel and the batteries to some extent.
> Battery bank charges to 13.7vdc and the are happy, panel sees a charged
> battery so it is happy.  I get that and it is cool thinking.
>
> But, what happens at AC failure??  How long will it stay up before going
> into Low Battery??  That would be the true test.
>
> I know it will depend on that actual load of the panel and devices but
> is it better or worse than a SLA??
>
> What kind of holder are you using to fit batteries or are you just
> soldering wires on the ends as a temp??
>
> Thanks,
>
> Les
>

With this first test, I was using 6 year old 18650 cells. They lasted 20
minutes before it went into low battery. I know this is terrible, but
these same cells would no longer hold a charge in a laptop.

I am using a plastic 4 battery holder specifically made for 18650 cells.
I then connect each 4 cell bank to a terminal bus strip in parallel.
 From there it goes to the charging circuit. I can add as many banks as
I like to get the desired backup time needed.

When connecting  battery banks in parallel, the key is to cross connect
the charging leads. At the first bank I connect only the positive lead,
and at the last bank I connect the negative lead. If you fail to follow
this important step, all the batteries in between will all die
prematurely. This is especially true with just about any battery. A
cross connection forces the charge to travel throughout all the battery
banks evenly. The batteries then balance themselves out without the need
of any additional balancing circuits that are commonly used on 18650
batteries.

I ordered some better made plastic battery holders from China, and I
have plenty of brand new 18650 cells. They should arrive in about a week
or so. It will take a few days to charge down & up the new banks with
the panel, so you will have to wait until then.

Jim Rojas

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