Want to switch from a cordless mower to a corded one. B&

[Inkidu]

Re: Want to switch from a cordless mower to a corded one. B&

Thanks for the help everyone. Points well taken.

Might need a large amount of amps at any one time.

So how about (2) 123A developer packs and use 8 cells to make a pack.

**broken link removed**

Obviously some things I need to research. I have found some info

on how to solder if you have a nice solder station, which I have.

**broken link removed**

Couple ?'s Do Ah add up like volts when cells are put in a series?

That is to say for instance do the (2) 17Ah batteries I have now

actually give 34Ah of use when connected in series?

It seems that charging can become a problem with Li-PO4 cells.

Is that true with all Li-PO4 batteries including the ones 123a sells.

I have seen Protection Circuit Module that are designed specifically for the

previously mentioned LiFePO4 cells(previous post), but could I just make (2)

smaller 4 cell packs that I could plug in series when I go to use them but

charge them separately. Obviously I won't hold anyone accountable for some

fairly significant bad repercussions. From what I have read these are the safest

Li-ion batteries out there and 123A have the best made of the LiFePO4 cells.

Maybe some good links on what to do and not to do might be helpful?

Researching something can be half the fun.

Thanks for any help.

 

[Inkidu]

Re: Want to switch from a cordless mower to a corded one. B&

I am progressively learning more this is some of what I have come up with now.

I am starting to see this as a possible solution. albeit still expensive.

This cell just came out. I want to go pretty big to avoid some bad things

happening by asking the battery to do to much. Thoughts on the solution?

https://www.batteryspace.com/lifepo...gerate32whwith6mscrewterminal-unapproved.aspx

And trickle charging with some thing like this. ( maybe just set on a 12 or 24

hour timer). This way I can test and keep and eye on what is happening

and feel the charging cycle out a little.

https://www.batteryspace.com/Smart-...V-8cells-LiFePO4-Battery-Pack-100-240VAC.aspx

I want to keep the current going in low because you should have a way to balance

the cells but I am trying to do this cheaply.

I calculate $280 with say another $20 for holders and connection plates.

https://www.batteryspace.com/component1pc60mmx20mmconnectionplateforseriesparallelconnection.aspx

One thing I wanted to learn with the project is how to solder cells but

considering the amount of vibration having solid mechanical connections

might make more sense. And while this will all be expensive I could have a

a very strong portable power source at the ready. I do some camping and

this pack could come in handy. That would be a lot of power in a 6 pound

package. (obviously more hardware would be needed but it is an idea.)

I could add to this as time goes by

and do or find ways to make it work. Installing some voltage readouts for the

cells would let me keep track of them and would be a cheap solution.

Taking it slow at first to feel the pack out. I am banking on the

safer chemistry of the cells to some degree.

Any opinions on the charger and/or the setup in general?

Thanks for any help.

 

[wizpic]

Re: Want to switch from a cordless mower to a corded one. B&

hi...
iam sure for which i write and itest it with my spicial tool andread battery manual and if you rread it you can belaive my note and :!: 1/10 :!: wrong

Added after 3 minutes:

I will say youre wrong, Like KMoffett a battery will not provide 17amps for one 1hr you have something called the Peukert law where is you take more than the 1AH then you have to apply the peukert's law and most batteries are rated at the 20hr rate.

For instance discharging at 10 amps does not remove twice as much power as discharging at 5 amps. It removes slightly more. Therefore a 100 amp hour battery (at the 20hr rating) could provide 5 amps for 20 hours, but it could not provide 10 amps for 10 hours. The available time would actually be slightly less.
You can use this equation:
C = "nominal" battery capacity. ie the number written on the battery or data sheet eg 100Ahrs
R = "hour rating" written on the battery or data sheet e.g. 20 hour
I = the "nominal" current at the given rate (ie C/R). i.e. how much current the battery can provide for the hour rating R. In this example 100/20 = 5 amps
n = Peukert's exponent eg 1.2 to 1.3 this is common for most batteries


T = C/(I/(C/R))n X (R/C)

We get:-

T = 100/(5/(100/20))n X (20/100)
T = 100/(5/5)n X (0.2)
T = 100/1 X (0.2)
T = 100 X 0.2
T = 20 hours, which we know to be correct.

so by doubling this discharge current should result in a bit less than half the time available. this due to Peukert's effect. Doubling the discharge current to 10 amps should result in a bit less than 10 hours available run time.

So has you can see if you double the amps to 10Amps it will only run for 8.1hrs

T = C/(I/(C/R))n X (R/C)
T = 100/(10/(100/20))n X (20/100)
T = 100/(10/5)n X 0.2
T = 100/(2)n X 0.2
T = 100/2.46 X 0.2
T = 40.6 X 0.2 = 8.1 hours

This one is a bit easier
T=C(C/R)n-1/In


17(17/20)n-1/17n = .69 hours (40 minutes)

wizpic

 

[Inkidu]

Re: Want to switch from a cordless mower to a corded one. B&

The whole post is about using a LiFePO4 battery as a replacement for lead acid battery in my B&D mower and how I might be able to do it cheaply. replacement battery is over $100


Well for anyone that is interested this is what I have done so far.

Hope it might help anyone. I have limited experience and I am open

for any help and corrections that I can get.

This order went to (shipped from USA, but not always the case though)

https://evcomponents.com/

So far so good but it is the first time I am dealing with them.


Headway 38120P 8ah
Code: H-38120p
8 $19.00 $152.00
Headway Bus Bar (2 cell)
Code: H-2Buss
7 $1.00 $7.00
Headway Cell Blocks (2 position)
Code: H-BLOCK ORANGE
8 $1.00 $8.00
Subtotal: $167.00
Payment surcharge: $5.63
Shipping cost: $20.66
Total cost: $193.29


I also got a constant current and then constant voltage charger from

Product Name Part No. Quantity Item Price Total Price
Smart Charger (3.0A) for 3.2V Li-FePO4 Battery Pack (1 cell, Standard Female Tamiya plug, 3.8V cut-off)

LFP-Cable-3.8V3A 1 $23.95 $23.95
Subtotal: $23.95
Discounts: -$1.20
Shipping & Handling: $8.41
Tax: $0.00
Order Total: $31.16


https://www.batteryspace.com/

My math $224.45 total but this is way under what it should probably cost,

a lot of short cuts are being taken, and the project has still yet to prove

itself. This is a learning experience that I hope will in the long run at least

teach me something. I would need to spend over $100 anyways for a bat.

I mention cccv because from what I have read so far this is the best way you

charge a LiFePO4 cell i.e. you begin with a constant current till you reach

around 3.6 volts and then you run a constant voltage and dump amps into

the cell. I don't pretend to know the exact process but this is what is

recommended. I only have a 1 cell charger, which means there will be lot

of hassle behind charging these cells, but I plan to babysit them until I feel

out what it takes to get the most useful life out of them. I am basically

going to act like the balance charger for some time. I am hoping that I won't

need to have a balanced discharge. I am not running a very big motor and

the drain won't be to much at any one time. (hopefully) This project was

started so I could get a hands on experience on how this all works.

Eventually I will upgrade the system but this is (I might be wrong) a way

to start.

Hope this helps and as always I welcome any input.

 

[Inkidu]

Re: Want to switch from a cordless mower to a corded one. B&

Update

For any one that is interested.

I have yet to receive more than one email or cells from evcomponents.

I placed the order on May 4

So I went another route. 15 Ah prismatic cells. There is actually 8.

Not the best looking lawnmower but it works.

I have used them with my lawnmower and I am pleased. These cells

can do an unbelievable couple hundred amps for minutes at a time.

Have yet to test in that way but so far so good. I had two cells go a

little low (volts) but I think it has more to do with how I made the pack.

Still learning.

My budget went out the window. Over $400 for the cells with another

$30 for the charger, which is only a single cell charger.

Still a little up in the air about the charger. Like the flexibility of the hobby

charges ( configure for other batteries and cell #'s) but would also like

the simplicity and probably superior engineered dedicated LiFePO4 charger.

I am up for suggestions??? I noticed someone named ecitypower on ebay

that has what look like good chargers but this is still an unknown.

Thanks for any help and I hope this will help any one in the future.