[RE-wrenches] Outback MX-60 - Li-ion charging
larrycrutcher
larry at starlightsolar.com
Wed Dec 1 18:18:22 EST 2021
Steve reminded me of something, probably because it is not very common. If you are recharging at 1C or greater rates, the Absorb cycle will need to be longer if you want to return all energy to the battery. Example: For a 300AH battery, 1C would be 300 Amps or over 16kW for a 48V bank.
Since it’s not economical to build a PV system that can fully charge from 100% DoD in just 1 hour of full sun, it’s not too likely you will use 1C charge rates. If you are generator charging, this may be true, in fact I recommend charging at 1C (or max the brand will allow) to reduce generator run time.
Larry Crutcher
On Dec 1, 2021, at 2:09 PM, Steve Higgins <steve at surrette.com> wrote:
I have found this to be true as well, especially when multiple LFP battery blocks are in parallel . I like to see the charge rate around the C2 to C8 Rate... the lower the charge rate the longer the absorb. On the LFP's we advise around 20-60 mins absorb time again depending on the amount of current availability, and quantity of parallel connections.
With the MX60 you can adjust the float voltage to the 3.65vpc, and set the timer for the rest of the solar day to ensure the batteries are getting balanced...
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On Wed, Dec 1, 2021 at 12:24 PM bob at midnitesolar.com <mailto:bob at midnitesolar.com> <bob at midnitesolar.com <mailto:bob at midnitesolar.com>> wrote:
Thanks Larry.
The information to stop when absorb voltage was reached is like, 10 or more years old and so I
don't know if that voltage reach and stop charging algorithm is still used by any BMS's.
This is probably why we had to add a logic input to tell the controller to stop charging from the BMS.
After the 0.3 hours at Absorb for balancing (which makes perfect sense for a BMS), does the MX/FM then
go to float at 3.65V per cell after that ?
Does your systems just restart a new bulk/absorb cycle the next morning or do you also do a Re-Bulk if
or when battery voltage falls below a certain point ?
Also, listening (reading) chat here on what might be needed that may not have been addressed by
Li battery, BMS and/or charge controller manufacturers.
Thanks,
boB
On 12/1/2021 12:03 PM, larrycrutcher wrote:
> If you stop charging a Li-ion battery when the CV (absorb voltage) is reached, you may reduce or stop the needed cell balancing time. We have had customers develop unbalanced series cells from continuous undercharging. Because of internal cell resistance, one cell will always reach saturation before others in the group. This can happen at less than 1mv difference. The more unbalanced a group of series cells are, the sooner one cells voltage will spike causing over voltage events at a lower terminal voltage.
>
> Our Li batteries (Elite Power Solutions-GBS and LiFeBlue) can be held at 3.65Vpc continuously, no problems. We have customers using both MX and FM controllers for 8 years now. Our recommended setting for the Absorb timer is 0.3 hours. This allows for cell balancing and for the capacity meter to recalibrate. Some chargers will stay at CV for several hours. No problems doing this either as long as cell voltage is lower than 3.8V (LFP chem.).
>
> Larry Crutcher
> Starlight Solar Power Systems
>
>
>
> On Dec 1, 2021, at 9:38 AM, bob at midnitesolar.com <mailto:bob at midnitesolar.com> wrote:
>
>
>
> Depends on the requirement for the BMS.
>
> Usually, but not 100% always, the requirement is to get the voltage up to "absorb" and then stop charging.
>
> Just set the min and max times very low, like 1 minute and that should satisfy that one.
>
> I do not remember if the MX60 had a Re-Bulk setting but I think it did ?
>
> The MX did not have a logic input for turning it on and off of course. OB had a communications
> device that converted their communications protocol to Modbus or Ethernet I think it was which
> may (or may not) be able to make it work.
>
> Could always buy something newer and keep the MX60 as a spare.
>
> boB
>
>
>
> On 12/1/2021 9:10 AM, frenergy wrote:
>> boB,
>>
>> Interesting...Sounds like this is not a candidate for L-ion batteries.
>>
>> Bill
>>
>> On 11/30/2021 10:47 PM, bob at midnitesolar.com <mailto:bob at midnitesolar.com> wrote:
>>>
>>> Hi Bill....
>>>
>>> As I remember, the min is of course... Minimum time in Absorb.
>>>
>>> Max is maximum time in absorb but depended on how long it took to get from Bulk MPPT to that Absorb voltage.
>>>
>>> So if it took 3 hours to get to Absorb that morning and you had t set for Max 2 hours, it would Absorb for 2 hours.
>>>
>>> If it only took 1 and 1/2 hours to reach Absorb voltage, the MX60 would Absorb for 1 and 1/2 hours.
>>>
>>> It worked "OK" but these days I would probably just set it for min of some 2 or 3 hours and then a max could be the same
>>> time or longer for FLA batteries.
>>>
>>> boB
>>>
>>>
>>>
>>> On 11/30/2021 7:16 PM, frenergy wrote:
>>>> Yes, the old one, not the FM. This oldie had an interesting way to set the absorption time. You would set the "min" time (in minutes) and you would set the "max" time (in hours, you have to set it to 1,2,3 or 4 hours).
>>>>
>>>> I need to know if I set the "min" to 10 minutes and the "max" time to one hour or two or three or four, how long will it stay in absorb?
>>>>
>>>> I called Outback and Megan there didn't know how this old fart works, apparently tech support isn't supporting us their old relics.
>>>>
>>>> Bill
>>>>
>>>> Feather River Solar Electric
>>>> Bill Battagin, Owner
>>>> 4291 Nelson St.
>>>> Taylorsville, CA 95983
>>>> 530.284.7849
>>>> CA Lic 874049
>>>> solar powered since 1982
>>>>
>>>>
>>
>>
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