[RE-wrenches] LiFePo4

Thu Sep 18 12:24:24 PDT 2014

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, boB at midnitesolar.com 
> <mailto:boB at midnitesolar.com> 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, boB at midnitesolar.com 
>> <mailto:boB at midnitesolar.com> 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, boB at midnitesolar.com 
>>> <mailto:boB at midnitesolar.com> 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 
>>>> <william at millersolar.com <mailto:william at millersolar.com>> 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
>>>>
>>>>
>>>>
>>
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> List Address: RE-wrenches at lists.re-wrenches.org 
> <mailto:RE-wrenches at lists.re-wrenches.org>
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive: 
> http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> www.members.re-wrenches.org
>
>
>
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Change listserver email address & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out or update participant bios:
> www.members.re-wrenches.org
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20140918/01ec6fe7/attachment-0002.html>