Microcontrollers > Data Logging

LiFePO4 repurpose with Arduino

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Simen:
DO remember that the optimal max charge voltage for LiFePO4 cells are 3.60V +/- 0.05V, NOT 4.20V as it is for LiCoO2/LiMnO2...

Bruce S:
I Plan on trying to make sure these reach only reach about 80 -90% of their full charge. From all the reading I could find on these, they like NiCds like being used and a full charge is only needed once in a while (First balancing charge being one of them).

For those who might have access to the DeWalt 36Vdc Hammer drills, my testing of these have found that it is the charger block on the inside that tells the whole system it's bad. I had a 4th block , but fully charging the system with a balancer fix it's problem.

My thought is to use the Arduino to charge these up to a set voltage ~13.4Vdc and leave it at that. The resting voltage was 3.3 on my HF free meter. I let it sit for a full 24hrs once I took off my little tester.

IF I balance these packs one at a time, then hook them up as a single unit I'll use it for the portable router and probably use a cutoff voltage of 12.8. This should give me a nice range.

Bruce S:
As part of this project I also am trying to make this:

More manageable.
The specs: UPS: Apc unit has cold start ability , but only a 12 7Ah battery.
Battery bank:13Vdc 48Ah AGM batteries Batteries are 6V 12Ah wired up for 12V gives me 12V @48Ah !!!
 The mil-spec router has a near constant draw of 12.5Vdc 1.3A with 3 CAT5 connections and 4 SSID connections all with MSN running on Chrome.

The UPS was really never meant to charge this many batteries, and it will eventually not be able to keep up with the current draw, hence the reasoning behind the large bank.
APC is known for constantly charging up batteries even once they are fully charged.
During my testing for charge, it puts out a voltage of 13.5 (No load ). I connected an AGM battery pack with a voltage reading of 12.3 , this UPS topped out at 0.25Amps. This is a constant. Once the battery's voltage was up reading 13.2 it was still running 0.25Amps.
It's nice having 2 digital meters!!
My PI eyed idea is this: hook up all the 6Vdc AGMs I have, let it charge them up and run the system. This poor little charging will take a week to completely recharge  :o.

The router has pretty interesting programmable settings. I have adjusted the minimum voltage cut-off to be 12.5 ( I know this is too low but the TEST battery is bulging and will not ever fit back into the case).  I was able to test that the cutoff works. This was important!

Once the weeks worth of charging for the battery bank is finished I will set the cutoff to be 12.8. Using the AGMs I should get about 30Ahrs of run time before the router shuts itself off due to voltage minimum at which point the UPS will continue to recharge the batteries.

Once ALL of this testing has done a repeated a few more times, I'll move the LiFePO4s into the spot for testing as well.
I know the Li batteries will not be able to last more than a couple hours (4 at most) but it's their portability that counts.  The AGMs are hard to beat when it comes to W/kg but this will be a good exercise in taking stuff that would normally be recycled and making them useful again.

NOT to mention all of the learning I will get.

george65:

--- Quote from: Bruce S on September 29, 2017, 02:42:46 PM ---The UPS was really never meant to charge this many batteries, and it will eventually not be able to keep up with the current draw, hence the reasoning behind the large bank.
APC is known for constantly charging up batteries even once they are fully charged.

--- End quote ---

I had a setup using an APC UPS with some solar panels and a couple of car batteries. I was running the outside fridge on it to play and learn.
I used a cheap PWM controller ( 2 in the end) to charge the batteries from the panels and had a Voltage relay module connected to the mains input so if the battery voltage went low at night, the UPS kicked in to charge them up.

The UPS always did seem to drive the battery voltage higher that I thought was ideal and now I know its the way those units are. The batteries didn't last long but they were old to start with and I figured all my mucking around just killed them. Maybe not that alone.
Supposedly you can alter the voltages in the setup of the UPS but mine is not new and I didn't have a suitable cable or was able to find the software to connect it to my laptop. I believe the units can also be configured to automatically hot start when the batterys are disconnected then re connected or hit minimum voltage. This would be a good feature to activate.

All the APC UPS units I have ( and there are a number of them) use the 7.2/ 7.5 Ah batteries but they are paralleled to give 24V. I was surprised reading yours was running 12V but then remembered you only run half the voltage we do so that probably explains it.
The units I have all use Anderson? Connectors from the unit to the battery pack . I got another and connected it to some battery cables and used that to connect to the car batteries.

I had quite a setup of controllers, SSR's and PWM modules to let me run things like a kettle which were over the UPS output rating and it was fun to play with and I learnt a lot as well.  It's all sitting in a box in the garage now and I keep seeing and missing playing with it. I'd like to play with it again as it's going to waste there but then I'd have to buy new batteries which would probably soon die so bit of an expense for nothing. Then again, I have a bit tied up in everything else now including a 2000W 24V Inverter I bought. Got it cheap and it's a great unit but just sitting there.
I was thinking/ wondering if I could just get a couple of those 7.2 AH batteries to power the UPS or inverter up and use it to power the hot water heater through the PWM controller.  Would probably switch off every time a cloud came over as there would be no power in reserve and I'd have to set a point on the variable PWM  which would probably be hopelessly inefficient with out some sort of automatic tracking.

One day I'll get my head enough around arduino to build the solar water heater controller and do things properly. I thught I saw something not too long back about how to run a grid tie inverter as a stand alone which may work but can't find the piece now so for the meantime, all the 24V stuff is gathering dust along with the 1.8KW of panels I had driving it all.

JW:


--- Quote from: george65 ---One day I'll get my head enough around arduino to build the solar water heater controller and do things properly.
--- End quote ---


Read these two books for using Arduino

https://steamautomobile.com:8443/ForuM/read.php?1,26164

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