## Re: [RoboMower] Re: LiFePO4

Expand Messages
• Hi Wofbob,   Yes, it s impossible to make 24V20AH with only 20 cells of 3.3V2.3AH. Divided 24V by 3.3V, 7 or 8 strings of cells should be connected in serial,
Message 1 of 18 , Feb 9, 2009
• 0 Attachment
Hi Wofbob,

Yes, it's impossible to make 24V20AH with only 20 cells of 3.3V2.3AH. Divided 24V by 3.3V, 7 or 8 strings of cells should be connected in serial, and divided 20Ah by 2.3Ah, 8 or 9 cells should be connected in parallel, so, at leat 7*8=56 cells will be needed.

Best regards,
Jerry

--- 09年2月10日，周二, wolfbob <wolfbob@...> 写道：

发件人: wolfbob <wolfbob@...>
主题: Re: [RoboMower] Re: LiFePO4
收件人: RoboMower@yahoogroups.com
日期: 2009,210,周二,7:36上午

I am having trouble with the math. The A123 is 3.3V at 2.3AH How do I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH or 33V at 4.6AH. I would think you would need 8 banks of 8 cells.

WBob

----- Original Message -----
From: Melissa
To: RoboMower@yahoogrou ps.com
Sent: Monday, February 09, 2009 7:53 AM
Subject: [RoboMower] Re: LiFePO4

> I think these are called A123 cells here in the US.

We're using these in our Gen 1 Automowers. We have 2 banks of 10, and
they fit right in the original battery case. The battery life between
charges is excellent. We've only used them one summer, so we don't
know how long the life span will be.

Melissa

[Non-text portions of this message have been removed]

___________________________________________________________
好玩贺卡等你发，邮箱贺卡全新上线！
http://card.mail.cn.yahoo.com/

[Non-text portions of this message have been removed]
• You d put n cells in parallel and then put those in series. OK, looking at more actual data, the A123 is 3.3v nominal, and 3.6v max at full charge. So 8x in
Message 2 of 18 , Feb 9, 2009
• 0 Attachment
You'd put "n" cells in parallel and then put those in series.

OK, looking at more actual data, the A123 is 3.3v nominal, and 3.6v max
at full charge. So 8x in series is 28.8v which the Robomower can take.
It will be 26.4v for the bulk of the discharge curve and that's slightly
better than the 24v nominal of the lead acid packs.

Anyhow, the 24V20AH "bike" packs discussed are LiFePO4 but NOT A123
brand. I don't know how many cells they put in parallel into each bank,
or the capacity of each cell, but apparently these are 8x parallel banks
in series. The voltage should be similar.

So to get something comparable in runtime to the 20AH lead-acid, you'd
need 8x of the 2.3AH A123's in parallel, or 64x total. At the eBay
price of \$8/cell (which seems to be the best deal right now) that's a
\$512 pack. The duct tape "bike packs" are \$300, but they're hardly the
proven quality of A123, and they're not rated for extremely fast charge
currents like A123. Which you may not care about, I mean you'd need a
bitchin powerful charger and balancing gear to get a >20A charge rate
which is a whole 'nother ball of wax.

I do not know if the Robomower's pack geometry would allow for 64x A123
cells to fit. I would think so though, they're not all that big.
Cooling can be a problem in densely packed configurations.

I was surprised to see someone just started listing 10x lots of A123
2.3AH cells at \$40. That is half what they've been running, but I think
the demand is so high the final selling price will be ~\$8 again.
Hundreds of people would jump at volume supply of \$4 cells. There are
no Completed Auctions on the 10x lots yet to gauge the price.

Danny

wolfbob wrote:
> I am having trouble with the math. The A123 is 3.3V at 2.3AH How do I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH or 33V at 4.6AH. I would think you would need 8 banks of 8 cells.
>
> WBob
>
>
> ----- Original Message -----
> From: Melissa
> To: RoboMower@yahoogroups.com
> Sent: Monday, February 09, 2009 7:53 AM
> Subject: [RoboMower] Re: LiFePO4
>
>
> > I think these are called A123 cells here in the US.
>
> We're using these in our Gen 1 Automowers. We have 2 banks of 10, and
> they fit right in the original battery case. The battery life between
> charges is excellent. We've only used them one summer, so we don't
> know how long the life span will be.
>
> Melissa
>
>
• WBob the automowers use 18v batteries not 24v you need to recalculate. ... I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH or 33V at
Message 3 of 18 , Feb 9, 2009
• 0 Attachment
WBob the automowers use 18v batteries not 24v you need to
recalculate.
--- In RoboMower@yahoogroups.com, "wolfbob" <wolfbob@...> wrote:
>
> I am having trouble with the math. The A123 is 3.3V at 2.3AH How do
I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH
or 33V at 4.6AH. I would think you would need 8 banks of 8 cells.
>
> WBob
>
>
> ----- Original Message -----
> From: Melissa
> To: RoboMower@yahoogroups.com
> Sent: Monday, February 09, 2009 7:53 AM
> Subject: [RoboMower] Re: LiFePO4
>
>
> > I think these are called A123 cells here in the US.
>
> We're using these in our Gen 1 Automowers. We have 2 banks of 10,
and
> they fit right in the original battery case. The battery life
between
> charges is excellent. We've only used them one summer, so we
don't
> know how long the life span will be.
>
> Melissa
>
>
>
>
> [Non-text portions of this message have been removed]
>
• A123 s cell is also of LiFePO4 chemistry. It s known to all the A123 s cell has very good performance in high power discharge and charge. But I m not sure
Message 4 of 18 , Feb 9, 2009
• 0 Attachment
A123's cell is also of LiFePO4 chemistry. It's known to all the A123's cell has very good performance in high power discharge and charge. But I'm not sure whether it is the best one.

I don't think A123's cell is necessary for RoboMower application. Generall high capacity cell will be OK.

Best regards,
Jerry

--- 09年2月10日，周二, Danny Miller <dannym@...> 写道：

发件人: Danny Miller <dannym@...>
主题: Re: [RoboMower] Re: LiFePO4
收件人: RoboMower@yahoogroups.com
日期: 2009,210,周二,10:35上午

You'd put "n" cells in parallel and then put those in series.

OK, looking at more actual data, the A123 is 3.3v nominal, and 3.6v max
at full charge. So 8x in series is 28.8v which the Robomower can take.
It will be 26.4v for the bulk of the discharge curve and that's slightly
better than the 24v nominal of the lead acid packs.

Anyhow, the 24V20AH "bike" packs discussed are LiFePO4 but NOT A123
brand. I don't know how many cells they put in parallel into each bank,
or the capacity of each cell, but apparently these are 8x parallel banks
in series. The voltage should be similar.

So to get something comparable in runtime to the 20AH lead-acid, you'd
need 8x of the 2.3AH A123's in parallel, or 64x total. At the eBay
price of \$8/cell (which seems to be the best deal right now) that's a
\$512 pack. The duct tape "bike packs" are \$300, but they're hardly the
proven quality of A123, and they're not rated for extremely fast charge
currents like A123. Which you may not care about, I mean you'd need a
bitchin powerful charger and balancing gear to get a >20A charge rate
which is a whole 'nother ball of wax.

I do not know if the Robomower's pack geometry would allow for 64x A123
cells to fit. I would think so though, they're not all that big.
Cooling can be a problem in densely packed configurations.

I was surprised to see someone just started listing 10x lots of A123
2.3AH cells at \$40. That is half what they've been running, but I think
the demand is so high the final selling price will be ~\$8 again.
Hundreds of people would jump at volume supply of \$4 cells. There are
no Completed Auctions on the 10x lots yet to gauge the price.

Danny

wolfbob wrote:
> I am having trouble with the math. The A123 is 3.3V at 2.3AH How do I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH or 33V at 4.6AH. I would think you would need 8 banks of 8 cells.
>
> WBob
>
>
> ----- Original Message -----
> From: Melissa
> To: RoboMower@yahoogrou ps.com
> Sent: Monday, February 09, 2009 7:53 AM
> Subject: [RoboMower] Re: LiFePO4
>
>
> > I think these are called A123 cells here in the US.
>
> We're using these in our Gen 1 Automowers. We have 2 banks of 10, and
> they fit right in the original battery case. The battery life between
> charges is excellent. We've only used them one summer, so we don't
> know how long the life span will be.
>
> Melissa
>
>

___________________________________________________________
好玩贺卡等你发，邮箱贺卡全新上线！
http://card.mail.cn.yahoo.com/

[Non-text portions of this message have been removed]
• OK..I am still lost... Two banks of ten give 33V at 4.6AH still not 18V either. If you are going to arrange 20 cells for 18V then I would think you would have
Message 5 of 18 , Feb 10, 2009
• 0 Attachment
OK..I am still lost...
Two banks of ten give 33V at 4.6AH still not 18V either. If you are going to arrange 20 cells for 18V then I would think you would have 5x4 for 16.5v & 9.2AH. Better to have 24 cells at 6x4 for 20V at 9.2AH.

I would think if these cells are going to be popular, then we should consider electronic designs in multiples of 3.3 volts, not the 1.5 volts of "old" batteries.

Once these "little" cells get popular in the automotive market, the price will plummet. A Hybrid car will use hundreds of these cells each and an electric car several hundred. I expect to see them under a dollar in 5-7 years so the idea of stuffing 50 of them into your mower is not too ridiculous.

WBob

From: bkelley9401
To: RoboMower@yahoogroups.com
Sent: Monday, February 09, 2009 6:45 PM
Subject: [RoboMower] Re: LiFePO4

WBob the automowers use 18v batteries not 24v you need to
recalculate.
--- In RoboMower@yahoogroups.com, "wolfbob" <wolfbob@...> wrote:
>
> I am having trouble with the math. The A123 is 3.3V at 2.3AH How do
I get to 24V and 20AH with 2 banks of 10?? I either get 6.6V at 23AH
or 33V at 4.6AH. I would think you would need 8 banks of 8 cells.
>
> WBob
>
>
> ----- Original Message -----
> From: Melissa
> To: RoboMower@yahoogroups.com
> Sent: Monday, February 09, 2009 7:53 AM
> Subject: [RoboMower] Re: LiFePO4
>
>
> > I think these are called A123 cells here in the US.
>
> We're using these in our Gen 1 Automowers. We have 2 banks of 10,
and
> they fit right in the original battery case. The battery life
between
> charges is excellent. We've only used them one summer, so we
don't
> know how long the life span will be.
>
> Melissa
>
>
>
>
> [Non-text portions of this message have been removed]
>

[Non-text portions of this message have been removed]
Your message has been successfully submitted and would be delivered to recipients shortly.