Yeah, CAN bus is used (was designed mainly) for automobiles and I bet EVs
had something to do with Lion battery BOS's being CAN.
We actually have a modbus (RS232) to CAN converter that could be used
for this
I think.
That kind of stuff isn't all that hard to do and you may find generic
devices to do this
conversion, but I have not looked into it.
boB
On 9/18/2014 12:08 PM, Starlight Solar Power Systems wrote:
boB,
IMPORTANT: If you ever plan to make a Li-ion control I/O, do it with
CAN bus. The whole industry is there. Our GBS product has CAN bus on
the CPU to control a variety of chargers now. I hope inverter and CC
manufacturers see this great potential. It would be easy for my CPU to
tell the Classic (or an inverter/charger) when and how much to charge.
It would be a real problem solver for me.
Larry
On Sep 18, 2014, at 12:52 PM, [email protected]
<mailto:[email protected]> wrote:
Oh, OK then. I thought that somebody had noticed a voltage drop when
surging.
When people ask me if they can use LFP or other Lithium chemistry
batteries, I tell them yes because
when they buy a LFP battery system, (or one of their Lithium Ion
relatives) it has all the protection
and balancing built into it. It's simple to use with an off the shelf
charge controller.
We were asked to add an input so that the LFP BMS could tell the CC
when to stop charging.
That was a special case and I don't remember who's system that was.
Normally, I see what you just
mentioned I think where it charges up to a voltage (Absorb) and then
immediately goes to Float
which would be some very low voltage, enough to be called "off".
Couldn't be easier.
Now we're just talking price compared to a tried and true LA battery ?
Some may remember Boeing's little problem recently though and that may
turn them off.
boB
On 9/18/2014 11:33 AM, Starlight Solar Power Systems wrote:
Truth is there is likely more than enough capacity in the LFP battery
the customer has but the manufacturer built a limit into the "box".
The limit of our battery is set to 10C for 30 seconds. WAY more than
any inverter can draw with even a small bank.
Larry
On Sep 18, 2014, at 12:26 PM, [email protected]
<mailto:[email protected]> wrote:
Yes, well of course there are these details.
If the LFP surge is a limitation, but not its amount of overall
energy storage, then you may have to add a very large amount of LFP
storage to overcome that which
could be overkill and cost a lot of extra $.
It's all a compromise.
boB
On 9/18/2014 10:55 AM, Starlight Solar Power Systems wrote:
boB,
When charging a LFP battery, the charge terminates when absorb
voltage is reached unless you have an enormous charger in which case
you will need to terminate based on AH returned. You would also need
to isolate the LA battery to finish charging it. Plus, LA needs
higher voltages than LFP. I don't think would solve Williams
problem. A better solution would be another LI-ion bank that is not
current limited. Just a 50AH bank could provide an additional 500amps.
Larry
On Sep 18, 2014, at 11:09 AM, [email protected]
<mailto:[email protected]> wrote:
One thing that could possibly be done is to have a smaller lead acid
battery in parallel with the LiFePo bank
so the LiFePo contains most of the "energy" storage, but the LA can
supply the surges and low impedance
source voltage.
boB
On 9/18/2014 8:53 AM, Starlight Solar Power Systems wrote:
William,
This is one reason I choose to avoid the "black box" approach to
Li-ion batteries for our customers. There are several companies
offering enclosed battery/controls like the OES. Their approach
does not match well to the off-grid and mobile markets that I serve.
Since most LFP batteries can handle 10C for up to 30 seconds
(Winston LFP can surge to 20C!) and 2C-3C continuous discharge, it
makes sense to me to design a protection system that can't utilize
that capability. Our LFMP battery has an external CPU that I can
program. We also use external high current relays for the
protective circuits so the full load of the inverter can be put to use.
With a LFP battery bank of 48 volts and 400AH, somewhat small for
off grid, the battery can operate continuously at 1200 amps or
about 60kW output and surge to 4000 amps/600kW. This obviously is
way beyond the demand capability of the inverter(s). A quick look
at the SI6048 data sheet shows maximum AC current is 11kW for 3
seconds.
I am glad you noticed the extremely low voltage sag under load.
This feature means lower current which should translate to longer
life for inverters. It also means starting loads that you can't
with a similar sized lead acid battery. A 1C load typically has
only 0.2 volt sag. For 48 volt systems, this means maintaining 51.2
volts throughout the full battery use. In fact, a 1C load will
still only have 0.2 volt drop until about 90% discharged. Simply
amazing.
Larry Crutcher
On Sep 17, 2014, at 10:15 PM, William Miller
<[email protected] <mailto:[email protected]>> wrote:
Larry:
......The internal battery management system will allow them to
disconnect under surge loads, just when you need your batteries to
stay connected. I will be conversing with the manufacturer to
learn more about them.
William
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