[ANSS-netops] ANSS-netops Digest, Vol 59, Issue 6
Patrick Bastien
bastienp at ldeo.columbia.edu
Wed Jan 7 20:59:29 UTC 2015
I confirmed it with the MPPT manufacturer. They said multiple chargers
feeding a common battery bank is fine, but multiple solar panels feeding
multiple charge controllers in parallel is not.
In general I think you can have multiple chargers (properly designed
chargers!) feeding a common battery bank because the bank will only
charge to the set point of the highest-voltage charger. For example if
one charger wants to have 14.4v for the absorption/constant-voltage
stage, but the other wants 14.2v, they will both charge until 14.2v when
the 14.2v charger will functionally go idle while the 14.4v charger will
continue until it reaches the 14.4v.
-Patrick
On 1/7/2015 1:40 PM, Greg Steiner wrote:
> Patrick, I'm curious as to how you get multiple MPPT controllers to
> charge a single battery bank. Are they inherently designed for this
> form of parallel operation?
> Greg Steiner
>
> On 1/7/2015 11:16 AM, anss-netops-request at geohazards.usgs.gov wrote:
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>> Today's Topics:
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>> 1. Re: solar power problems (Patrick Bastien)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Wed, 7 Jan 2015 12:18:20 -0500
>> From: Patrick Bastien <bastienp at ldeo.columbia.edu>
>> To: <anss-netops at geohazards.usgs.gov>
>> Subject: Re: [ANSS-netops] solar power problems
>> Message-ID: <54AD6A5C.6080608 at ldeo.columbia.edu>
>> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
>>
>> The Concorde Sun Extender PVX-1040T has a nominal capacity of 104AH, so
>> 312AH for the northern TA stations and 208AH for the southern TA
>> stations.
>>
>> Beginning late last summer, the LCSN has begun to switch from older
>> PWM-style charge controllers to MPPT charge controllers. Although it is
>> too soon to say something definite, this is seeming to have a larger
>> effect on station up-time than just adding more panels or batteries.
>> Something I am doing that might be considered non-standard is wiring
>> each solar panel individually to its own small MPPT change controller.
>> This allows each solar panel to generate the maximum amount of power
>> regardless of the lighting condition of the other solar panels. The
>> several MPPT charge controllers then feed a common battery bank. I then
>> regulate the voltage powering the sensor by using a small low-noise DCDC
>> converter imbedded inside a cable. The MPPT benefits might be magnified
>> for the LCSN because of the location of many of our solar powered
>> stations are in forests or forest-adjacent.
>>
>>
>> Patrick Bastien
>> LDEO-LCSN
>>
>> On 1/7/2015 11:06 AM, Meremonte, Mark wrote:
>>> Bob, May I ask the AH size of AGM batteries for an average TA
>>> station? Thank you, Mark
>>>
>>> On Wed, Jan 7, 2015 at 8:29 AM, Robert Busby <busby at iris.edu
>>> <mailto:busby at iris.edu>> wrote:
>>>
>>> Hi Mitch et al.
>>> This is a good discussion of Power for seismic stations, thanks.
>>>
>>> In the Transportable Array deployment, all 1717 stations
>>> operate(d) off solar power for at east two years. The average
>>> current draw for a station is 0.5Amps on a 12V system, but can
>>> vary from 0.4 to 0.6A depending on the telemetry system. High
>>> current telemetry systems such as VSAT are powered separately. We
>>> avoided AC power because of the proximity of noise due to pumps,
>>> motors, etc.
>>>
>>> In general we use (2) 90W PV panels and (2) AGM Lead Acid
>>> batteries for stations south of the Kentucky/Tennessee line (row U
>>> in TA station codes) and (3) 90W PV panels and (3) AGM Lead Acid
>>> batteris north of there. Shady or snowy sites occasionally got
>>> more panels and batteries. For permanent stations I'd go with the
>>> (3) PV and 3 or 4 batteries. We prefer good quality batteries
>>> designed for solar applications, such as the Concorde Sun Extender
>>> PVX-1040T. We use PWM regulators with Low voltage disconnect at
>>> 10.8V. A few more sophisticated options are discussed below.
>>>
>>> I would concur with the notion that the most effective way to
>>> improve a marginal station power situation is to add 1 or 2
>>> batteries, and often this can be done without much infrastructure
>>> alteration. And the next option is to add a panel. There is
>>> little concern about over driving the charge controller with too
>>> much current from too many panels. In Alaska, the "more
>>> batteries" approach is taken to extremes in which stations have 24
>>> batteries to float through the winter. I would also concur that,
>>> to date, neither wind nor fuel cells have proved reliable enough
>>> to warrant their use, especially in permanent stations of the
>>> Lower48.
>>>
>>> More complexity described below:
>>> Our system has, in addition to the main battery bank, a small
>>> reserve battery. When the system switches to the reserve, certain
>>> loads such as the telemetry radio and local data storage are duty
>>> cycled at four hour intervals. This reduces the power of the
>>> station to about 3W, yet still provides complete telemetry (though
>>> with episodic latency) and complete local storage. For us, this
>>> reserve power serves to identify the source of the outage is
>>> clearly power as opposed to a host of other possibilities. In the
>>> original design this reserve battery was Alkaline Lattern 30AH
>>> batteries [(3) x 6Volts] (a primary battery, disposed of after
>>> use). More recently, We have also used 100-300AH rechargeable
>>> batteries that are then connected to the main batteries using a
>>> battery isolator circuit-which connects the reserve batteries to
>>> the charger only when the main battery has recharged to 13.2V. We
>>> add a 10A current limit to the battery interconnection. The
>>> reserve power load shedding can be thought of as doubling the
>>> capacity of the reserve batteries, reducing the cost of overall
>>> power system for this reserve capability. Without that
>>> sophisitication of load shedding, adding more batteries is
>>> effective but there is a cost in terms of station uptime. When a
>>> very large, undifferentiated battery bank is depleted, it will
>>> take a longer time for the batteries to reach the reconnect
>>> voltage. In this time, the station itself could be operating on
>>> the minimal power produced. We keep the main battery bank fairly
>>> modest so it recovers voltage quickly, and defer recharging the
>>> reserve pack until there is ample power-sometimes weeks, or in
>>> Alaska, months later. Its meant to get you through an ocasional
>>> bad spell. One issue in this reserve battery switching is the dc
>>> currents can introduce magnetic pulses seen on the
>>> seismometer-particularly Trilliums within a few meters of the
>>> switches.
>>>
>>> If you are plannning a Net-ops meeting in the future, I'd be
>>> happly to elaborate on the power system for Alaska, which uses a
>>> Genasun MPPT charge controller and LiFePO4 (Lithium Ion) batteries
>>> and the same duty cycle loads, reserve battery concepts. These
>>> significantly reduce the weight of a 1440AH system to 420 lbs and
>>> do not require derating the capacity for cold temperatures. They
>>> are very expensive, but not as much as a helicopter trip.
>>>
>>> Bob Busby
>>> TA Manager
>>>
>>> On 1/6/2015 7:36 AM, Kyle Persefield wrote:
>>>
>>> Mitch,
>>>
>>> My 2 cents worth
>>>
>>> Because of cost, we have found throwing on more solar panels
>>> to be the
>>> cheapest and least maintenance intensive solution. Fuel
>>> cells and
>>> thermoelectric generators are expensive and then there is the
>>> recurring
>>> cost for fuel, getting fuel to the site, then monitoring of
>>> the fuel
>>> supply level to consider, and the added required maintenance.
>>> We have not
>>> found a solution to use these devices as demand requires their
>>> use. Or
>>> turning them on and off as needed. So long as there is fuel
>>> they are on.
>>>
>>> We have been very disappointed with wind turbines. The
>>> smaller ones,
>>> which are designed for the consumer market, the bearings
>>> always fail.
>>> Expect no more than 2 or3 years out of these "cheap" units.
>>> Then of
>>> course there is the need for wind. No wind for extended
>>> periods is just
>>> as bad as your overcast scenario.
>>>
>>> Kyle
>>>
>>> -----Original Message-----
>>> From: ANSS-netops
>>> [mailto:anss-netops-bounces at geohazards.usgs.gov
>>> <mailto:anss-netops-bounces at geohazards.usgs.gov>] On
>>> Behalf Of Mitchell M Withers (mwithers)
>>> Sent: Monday, January 05, 2015 7:12 AM
>>> To: Philip Crotwell
>>> Cc: anss-netops at geohazards.usgs.gov
>>> <mailto:anss-netops at geohazards.usgs.gov>
>>> Subject: Re: [ANSS-netops] solar power problems
>>>
>>>
>>> Here is a snippet from a recent report from a visit to an
>>> example station
>>> with a reftek, three S-13's, and an episensor. Stations vary
>>> of course
>>> and we do use low voltage cutouts at every station (fancy ones
>>> that cut
>>> out the transmitter first, then the DAS and everything else if
>>> the voltage
>>> continues to get lower).
>>>
>>> "The new battery banks, when installed were at 12.95 and
>>> 12.98. The total
>>> station draw is exactly 600ma (checked continuously for about
>>> three
>>> minutes). I did a quick calculation of 4 batteries at 96AH
>>> each, 384/.6 =
>>> 640/24 =26.6 days. This calculation would assume no solar
>>> charge, but does
>>> not take into account reduced battery capacity due to cold
>>> temperatures."
>>>
>>> The panels at that particular station were supplying about
>>> 700ma together
>>> on an overcast day and are being replaced with bigger panels
>>> this week.
>>> Of course one solution is more battery and more solar at every
>>> station
>>> along with more frequent refreshing of batteries. But that
>>> gets expensive
>>> and time consuming so I was fishing to see if anyone is doing
>>> something
>>> creative. (e.g. wind or hamster wheels).
>>>
>>> Mitch
>>>
>>> Center for Earthquake Research and Information (CERI)
>>> University of Memphis Ph: 901-678-4940
>>> Memphis, TN 38152 Fax: 901-678-4734
>>>
>>>
>>> ________________________________________
>>> From: Philip Crotwell <crotwell at seis.sc.edu
>>> <mailto:crotwell at seis.sc.edu>>
>>> Sent: Monday, January 5, 2015 7:50 AM
>>> To: Mitchell M Withers (mwithers)
>>> Cc: anss-netops at geohazards.usgs.gov
>>> <mailto:anss-netops at geohazards.usgs.gov>
>>> Subject: Re: [ANSS-netops] solar power problems
>>>
>>> Hi
>>>
>>> How did you come up with your 25 day figure? Can you put some
>>> numbers on
>>> power input and output?
>>>
>>> We use two 105 amp-hour batteries per station, where the load
>>> is about
>>> 1/2 an amp. That gives me about 17.5 days theoretically,
>>> but my
>>> understanding is that you never want to discharge batteries
>>> anywhere near
>>> their rating as they can be damaged by high discharges. So
>>> maybe worry
>>> less about age and more about installed capacity, ie double
>>> the battery
>>> and replace them half as often.
>>>
>>> We also, because of the cell modems, can monitor the battery
>>> voltage over
>>> time, we have a cron job to ping the cell modem once an hour
>>> and ask it
>>> what the input voltage is. For example here is the last few
>>> days at one
>>> station. You can definitely tell the difference between sunny
>>> days and
>>> rain, and we get a heads up if the power is getting low and
>>> can do
>>> something before the station goes down.
>>> http://eeyore.seis.sc.edu/earthworm/status/HAW_last720.png
>>>
>>> Here is another station that we are becoming worried about,
>>> looks like I
>>> might get to go on a road trip soon!
>>> http://eeyore.seis.sc.edu/earthworm/status/CASEE_last720.png
>>>
>>> Philip
>>>
>>> On Sun, Jan 4, 2015 at 9:07 AM, Mitchell M Withers (mwithers)
>>> <mwithers at memphis.edu <mailto:mwithers at memphis.edu>> wrote:
>>>
>>> Many of our stations run on battery and solar and that
>>> normally works
>>>
>>> well. We have a routine battery replacement cycle to make
>>> sure they don't
>>> get old. Theoretically, we should be able to run with zero
>>> solar for
>>> about 25 days. But this has been an unusually dreary winter
>>> in the
>>> southeast and we haven't had much sun for the past two months
>>> or more.
>>> I'm wondering what others do in areas with limited sunlight to
>>> power
>>> stations that don't have AC available?
>>>
>>> Mitch
>>>
>>> Center for Earthquake Research and Information (CERI)
>>> University of Memphis Ph: 901-678-4940
>>> Memphis, TN 38152 Fax: 901-678-4734
>>>
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>>>
>>> --
>>>
>>> ============================================================
>>>
>>> Robert W. Busby
>>> Transportable Array Manager 508-801-7628
>>> USArray / EarthScope 37 Haynes Avenue
>>> www.earthscope.org/usarray <http://www.earthscope.org/usarray>
>>> Falmouth MA USA 02540-2312
>>>
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>>>
>>>
>>>
>>> --
>>> *********************************************************
>>> Mark Meremonte Geophysicist
>>> U.S. Bureau of Reclamation: Seismotectonics & Geophysics Group
>>> Denver Federal Center Work: 303-445-3298 Cell: 303-808-3894
>>> POBox 25007, 85-833000Email: mmeremonte at usbr.gov
>>> <mailto:mmeremonte at usbr.gov>
>>> Denver, CO 80225 Web: http://www.usbr.gov
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>>> 80225
>>> **********************************************************
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