Battery bank switching

CariboocootCariboocoot Posts: 17,615Banned ✭✭
Okay, I'm certain some of you must have a dual "A or B" battery bank set-up. My question is: what do you do to switch from bank 'A' to bank 'B' when necessary?

I'm thinking of adding a back-up bank that would charge when the main bank is in 'Float', to be used on those wonderful cloud-filled days when the panel output is about 1/3 normal. Manually moving wires is possible, as is flipping DC breakers. But, is there any sort of solenoid-controlled switch that could do the job triggered by low voltage state? Say the same circuitry normally used for starting a genset. I do realize that any such switch involved would have to be heavy enough to handle (in my case) about 200 Amps max. And also you wouldn't want the solenoid to remain engaged just to maintain power: it would have to 'flip' the switch on. Resetting would be another issue. For seamless operation there might need to be a moment of both banks connected so that there is no danger of power interruption to the inverter.

Just thinking out loud again. :D

Comments

  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Battery bank switching

    Marc,

    Are you trying to figure out the charge side or the load side? For the charge side,, some controllers,, (Like the BS 2512i series )will shut excess current to a second battery. On the load side,, a voltage controlled relay that switches at a predetermined voltage would switch from bank A to bank B. Any relay or solenoid system should be set up to only draw current in it's switching . Solenoids draw considerable current when energized. The advantage of a relay is that you can use a relay to trigger a relay,, drawing only small currents. I bet there is such a system out there.

    On the other hand,, a manual transfer switch like they use in boats will control the load pretty easily.

    Tony
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Battery bank switching

    try switches like these.
    http://store.solar-electric.com/basw1300amp.html
  • _OS__OS_ Posts: 204Solar Expert ✭✭✭
    Re: Battery bank switching

    Also check out this blog:
    System Automation for a Spare Battery Bank
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Battery bank switching

    Thanks, guys!

    Yes it's the supply side I'm concerned with. The MX60 has a nice AUX function capable of firing a relay that can connect bank 'B' when bank 'A' reaches float. But automating the supply-side switching is another issue due to the potentially high current involved.

    Bill - I went looking for those switches last night and couldn't find them! Must have typed "aardvark" instead of "switch" in the search box - again. :p Now I'm wondering if I can rig up a manual actuator for it. The only reason it would be necessary is if I wasn't about sometime when the voltage got low - it's happened once on the old system and we came back to a sour 'frige.

    So now I'll be weighing up the costs of this against just a bigger primary bank.

    More panels ... need more panels ... :p
  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Re: Battery bank switching
    Bill - I went looking...

    Niel?

    An "interesting" bank switcher (when charging, connects two banks together. When discharging, disconnects banks; 0.1 amp standby, 8 watt with relay on).

    Similar product from Xantrex.

    Here is a nice coil (with lower operating power?) from Blue Sea.

    One thing to be careful with some battery switches... they have an "OFF" position which (if wired according to some instructions I have seen) disconnects the battery bank from the engine driven alternator + loads... Many alternators and generators cannot accurately regulate their output current when the motor is running--potentially taking out any connected loads (lights, electronics, etc.)...

    You should (usually) only switch the bank switch when the batteries are under light/no loads and any engine driven charger is turned off.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Battery bank switching

    Yes, I meant Niel. :blush:

    See? I have warned you all about my 'brain'! :p

    Note to self: get one of those electronic brains ....
  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Re: Battery bank switching

    That's OK--all of us moderators look alike. :p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JESSICAJESSICA Posts: 289Solar Expert
    Re: Battery bank switching

    A somewhat similar question:

    Does anyone know about a switch that would let me connect two different inverters to the same battery bank?

    Battery bank: 24 volts, 200 amps.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Battery bank switching
    JESSICA wrote: »
    A somewhat similar question:

    Does anyone know about a switch that would let me connect two different inverters to the same battery bank?

    Battery bank: 24 volts, 200 amps.

    The switch mentioned above by Niel (hey I got the name right!) would do this if wired 'backward': i.e. two inverters instead of two battery banks.

    But why? Inverters wired with proper fusing and disconnects would take care of themselves, providing you don't mean two different voltage inverters. Outback Inverters are meant to be wired to the same bank when 'stacked'. What exactly are you trying to achieve? (Catch me quick before my brain quits again. :p )
  • JESSICAJESSICA Posts: 289Solar Expert
    Re: Battery bank switching
    The switch mentioned above by Niel (hey I got the name right!) would do this if wired 'backward': i.e. two inverters instead of two battery banks.

    But why? Inverters wired with proper fusing and disconnects would take care of themselves, providing you don't mean two different voltage inverters. Outback Inverters are meant to be wired to the same bank when 'stacked'. What exactly are you trying to achieve? (Catch me quick before my brain quits again. :p )

    Cariboocoot:

    Thanks

    My system is a rather small one. My inverter, exeltech 1100, is powerful enough to run the gadgets I usually need to run. But sometimes, I need to power a water pump (craftman, ½ horsepower, 11 amps) and the exeltech is just not up to the task. When that inverter failed some time ago, a friend of mine gave me an old Aims 3,000 modified wave, which works well, but I don’t want to use it with my tv, computers, etc. Thus, whenever I need to use the water pump, I have to disconnect the exeltech, connect the Aims…and, well, it is just too much trouble. So, after reading your post I ask: Are you saying I can just connect BOTH inverters to my battery bank and then use whichever I need to use any given moment?
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Battery bank switching
    JESSICA wrote: »
    Cariboocoot:

    Thanks

    My system is a rather small one. My inverter, exeltech 1100, is powerful enough to run the gadgets I usually need to run. But sometimes, I need to power a water pump (craftman, ½ horsepower, 11 amps) and the exeltech is just not up to the task. When that inverter failed some time ago, a friend of mine gave me an old Aims 3,000 modified wave, which works well, but I don’t want to use it with my tv, computers, etc. Thus, whenever I need to use the water pump, I have to disconnect the exeltech, connect the Aims…and, well, it is just too much trouble. So, after reading your post I ask: Are you saying I can just connect BOTH inverters to my battery bank and then use whichever I need to use any given moment?

    Yes, but no. :roll:

    Provided both inverters are the same voltage and have their own fuse & disconnect there's no reason they can't both run off one bank; they won't inter-act. I am assuming charging is coming from a separate source, like solar panels feeding a charge controller which feeds the batteries. If one of the inverters has a built-in charger, sourced from a generator say, that's okay too. If they both have gen-chargers you have to determine which is the best for re-charging the batteries.

    The bad news is your water pump motor isn't going to like the modified sine wave. At 1/2 HP, it is almost certainly an AC induction motor. Without getting too technical, it will seem to be low voltage to the motor. If it runs at all, it will strain. Possibly it won't get up to speed which will burn it out pronto. In any case, the MSW will shorten its life.

    Oddly enough, the things people most fear won't run off MSW, computers, usually have no trouble with it at all. They have extremely sophisticated power supplies that can stand quite a variation in input signal. It's necessary because their power requirements at the circuit board level are very fussy.
  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Re: Battery bank switching

    You can read about MSW and TSW inverters here (FAQs):

    All About Inverters
    Choosing an inverter for water pumping

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Posts: 1,341Solar Expert ✭✭✭
    Re: Battery bank switching
    BB. wrote: »
    Here is a nice coil (with lower operating power?) from Blue Sea.

    That looks suspiciously like the doohickey under the hood connecting the engine and house batteries on my camper van.

    And, I left the lights on and ran the engine battery down once, and turning on the key did not connect the batteries - I know since the truck still wouldn't start. (But I was able to jump start the engine from the house battery.)

    And, there is an LED down at the bottom of the dash which is always on when the engine is running, but which I haven't bothered to track down yet.

    So now I'm pretty sure what that doohickey is. I had originally thunk it was just a simple connecting coil, but it appears to be smarter than that. Maybe I'll keep it. :)
  • _OS__OS_ Posts: 204Solar Expert ✭✭✭
    Re: Battery bank switching

    Victron Energy also makes battery isolators:
    Argo FET Battery Isolators

    I believe these devices are meant to be used when you have a starter battery in addition to the main batteries. I would use relays instead as described above.

    OS
  • JESSICAJESSICA Posts: 289Solar Expert
    Re: Battery bank switching
    Yes, but no. :roll:

    Provided both inverters are the same voltage and have their own fuse & disconnect there's no reason they can't both run off one bank; they won't inter-act. I am assuming charging is coming from a separate source, like solar panels feeding a charge controller which feeds the batteries.

    The bad news is your water pump motor isn't going to like the modified sine wave. At 1/2 HP, it is almost certainly an AC induction motor. Without getting too technical, it will seem to be low voltage to the motor. If it runs at all, it will strain. Possibly it won't get up to speed which will burn it out pronto. In any case, the MSW will shorten its life.

    Cariboocoot:

    Yes, both inverters are same voltage, and there will be no problem adding a new breaker for the second inverter. I addition, you are right, power to the batteries comes from 6 pv panels, via an mx60 controller.

    As I said, when the exeltech failed, I used the Aims to run almost everything, and the water pump ran with no audible or visible strain, until the exeltech was fixed four months later...

    Thanks.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Battery bank switching

    JESSICA;

    That is good!
    If your water pump runs off an 1100 watt inverter I suspect it's not the standard, 1/2HP AC induction motor. On start-up such a motor would send the inverter into over-load fault. Or maybe this is why the Exeltech failed? Too much time in 'surge'.

    Anyway, the question of dual inverters comes up from time to time. Usually it's someone who wants to run a small inverter to handle daily loads and only operate a large one when necessary. The stand-by power drain of a bigger inverter is bigger, so when power is scarce it can make sense to do this.

    Cheers!
  • mike95490mike95490 Posts: 7,917Solar Expert ✭✭✭✭
    Re: Battery bank switching

    While you can parallel the 12V (input) side of any inverter, and just switch it off, when not needed, don't even think of trying to tie the 120V output side to anything else, but your loads. Very few inverters will parallel outputs without a big fountain of sparks.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • DCDaddyDCDaddy Posts: 3Registered Users
    Okay, I'm certain some of you must have a dual "A or B" battery bank set-up. My question is: what do you do to switch from bank 'A' to bank 'B' when necessary?

    I'm thinking of adding a back-up bank that would charge when the main bank is in 'Float', to be used on those wonderful cloud-filled days when the panel output is about 1/3 normal. Manually moving wires is possible, as is flipping DC breakers. But, is there any sort of solenoid-controlled switch that could do the job triggered by low voltage state? Say the same circuitry normally used for starting a genset. I do realize that any such switch involved would have to be heavy enough to handle (in my case) about 200 Amps max. And also you wouldn't want the solenoid to remain engaged just to maintain power: it would have to 'flip' the switch on. Resetting would be another issue. For seamless operation there might need to be a moment of both banks connected so that there is no danger of power interruption to the inverter.

    Just thinking out loud again. :D

  • DCDaddyDCDaddy Posts: 3Registered Users
    Not sure of the setup but I have a relay switch that switches incoming power from Bank A over to Bank B,  which is based upon the Low Level Voltage setting (14.5Vdc) on a Monitoring Relay. This Monitoring Relay is between the power unit (12vdc-2A) and the two Battery Banks. Now when discharging, Bank A reaches the pre-set 14.5V, then the discharge power is disconnected by the Relay and after a brief pause, Power is re-connected to Bank A for charging. The Cut-off for charging is 16.0V.

    Now the Relay allows/transfers discharge of Bank B. This repeats itself continuously so there will always be power 24/7.

    Always program cut-off to recharge for a Rest period of 40 minutes minimum (+/- in respect to the 18650 battery cell)  before charging any of these two or more banks.


  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Why do you think you need an A+B battery bank? For boats and other vehicles, that is usually done so that if somebody runs the "house" batteries dead, they can still use the alternate bank to start the motor (recharge, not stranded, etc.).

    In general, a 2x larger battery bank is stressed 1/2 as much. Less maintenance and longer battery life.

    Regarding 18650 Batteries--You are talking about Li Ion batteries. This is a whole 'nother kettle of fish. Improperly configured and monitored Li Ion batteries with poor charging/discharging safety/control--At best, probably trash an expensive battery bank. At worst, explosions, fires, and possible Hydrofluoric acid contamination to your home/property (HF acid is really scary--Both short term and long term health effects--Including death at low concentrations).

    In addition to being a highly corrosive liquid, hydrofluoric acid is also a powerful contact poison. Because of the ability of hydrofluoric acid to penetrate tissue, poisoning can occur readily through exposure of skin or eyes, or when inhaled or swallowed. Symptoms of exposure to hydrofluoric acid may not be immediately evident, and this can provide false reassurance to victims, causing them to delay medical treatment.[11] Despite having an irritating odor, HF may reach dangerous levels without an obvious odor.[7] HF interferes with nerve function, meaning that burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.[11] Symptoms of HF exposure include irritation of the eyes, skin, nose, and throat, eye and skin burns, rhinitis, bronchitis, pulmonary edema (fluid buildup in the lungs), and bone damage.[12]

    Once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. Burns with areas larger than 160 cm2 (25 square inches) have the potential to cause serious systemic toxicity from interference with blood and tissue calcium levels.[13] In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity.[14] In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel[15][16][17] or special rinsing solutions.[18][19] However, because it is absorbed, medical treatment is necessary;[13] rinsing off is not enough. Intra-arterial infusions of calcium chloride have also shown great effectiveness in treating burns.[20]

    Lithium Ion Battery flashlight explosion:


    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DCDaddyDCDaddy Posts: 3Registered Users
    Two separate battery banks is called for in my use, but not for everybody of course.
    The question was the relay of power and controlling rather output to loads or input to charge a battery.....right?
    Power can be taken or made from any storage source. It is how you monitor and control that power.


  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    There are bi-stable (latching) DC relays with pretty high current ratings:


    You can get silicon relays that, while not latching, draw very little power to switch--Generally, these have higher resistance than mechanical contacts and need to be well heatsinked to prevent overheating/failure. And they are not cheap either:


    Low voltage/high current DC is always difficult to switch. If you can do this another way (controlling loads to turn them off electronically, etc.) is usually better.

    Measuring DC current usually falls back to the precision power resistor (shunt) with "Kelvin Contacts" (large connectors for high current connections, a pair of small connections for the millivolt meter), usually placed in the return lead (negative lead of a negative ground battery system). Use a millivolt compatible ADC (analog to digital converter) and you have a pretty accurate measuring system:


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Posts: 27,906Super Moderators, Administrators admin
    Just to give an example of how DC current is much more difficult to control vs AC (note that the "arc voltage" is usually just over 12 VDC--So higher voltage DC is even more difficult to control--Think DC Arc Welders):


    If you wish to continue the discussion--I will split this into your own thread (easier to talk about your system needs and not confuse with older thread/discussion).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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