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Author Topic: Battery as a dump load  (Read 6973 times)
billi
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« on: January 16, 2011, 10:22:24 AM »

Can one connect a second battery  (same voltage ) to the  main Battery  as a dump load ?

Would there be too many amps flowing or too little ? Assume thats hard to say

But somehow it would make sense  to have a cheap second battery charged

Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
clivejo
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« Reply #1 on: January 16, 2011, 10:30:36 AM »

What happens when the second battery is full?  Wouldn't it be better connecting the two batteries in parallel and keep the dump load as a fail-safe as its designed to do?
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billi
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« Reply #2 on: January 16, 2011, 10:34:01 AM »

the idea is to start a cheap inverter then ,  with a voltage controlled relay   to divert   power to AC consumer(s)

Its not only for a Windturbine , more or less to avoid PV not pushing all available power into batteries when in absorption/float mode
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Billy
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« Reply #3 on: January 16, 2011, 10:46:01 AM »

billi, billy here.

I thought about that.  Seemed a waste to be dumping all that lovely power only to assist global warming.   facepalm

My idea was to spit the batteries in two and always have a low bank that needed charging.  Trouble is I was going to kill the batteries in a rather short time.  You could end up with 180 cycles a year.

Off grid I reckon the amount of energy actually converted for my use is quite small, probably less than 25% so I am keen to make the best use of it.

What are you doing with all this power you are making?  Not brewing I hope.

billy

 Grin Grin Grin
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clivejo
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« Reply #4 on: January 16, 2011, 10:49:24 AM »

I think you would need to be careful how the dump load operates.  If it just connects in-line with a relay you could risk huge current flows and burn out your cables.  For example if you have a fully charged battery and connect it to an empty battery, current will flow from the full battery to the empty in an attempt to equal out, this will involve a large current flowing between them.

Dump loads tend to have calculated resistance, in order to safely disperse any extra power being generated.  With batteries resistance varies with charge level and voltage, making it very unpredictable.

Is there no way of starting the inverter slightly below your dump load threshold ?  This way the inverter load should prevent the dump load kicking in, but also keeps your batteries fully charged?
« Last Edit: January 16, 2011, 10:53:53 AM by clivejo » Logged
billi
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« Reply #5 on: January 16, 2011, 11:11:25 AM »

only distilling  Billy   extrahappy

Our consumption  went up a fair bit , since my 3 year old knows how to control all the gear  whistlie and much more washing  machine use

But beside this  it is always good to know  to have 4 or 5 kwh stored in a spare battery   and if needed just hook it into the victrons   and charge the main battery

Clivejo  true  and i would like to find out  how much current we are talking about , but the charge controller wil stop that current when the main battery gets below voltage setpoints

To use my relay in the inverter would be an alternative , but not a permanent one cause will not allow my chargecontroller to optimal charge the main bank

Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
clivejo
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« Reply #6 on: January 16, 2011, 11:23:52 AM »

Do you have a main inverter?  You could set a high battery threshold to trigger a high load device (ie immersion heater)  this way you are making the most of the energy you are generating.

Also most batteries don't like being 'empty' for extended periods of time.  By regularly leaving a battery empty it will reduce its life.
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clivejo
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« Reply #7 on: January 16, 2011, 11:33:09 AM »

only distilling  Billy   extrahappy

Clivejo  true  and i would like to find out  how much current we are talking about , but the charge controller wil stop that current when the main battery gets below voltage setpoints


Depends on the capacity of both your battery banks and the difference in the level of charge, also the type of battery.  But its more than likely to do damage, either damage the wiring due to over current or your batteries due to over charging/discharging.  A high charge or discharge will damage plates in wet batteries
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Justme
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« Reply #8 on: January 16, 2011, 12:48:37 PM »

Downsides

need to keep bat SOC low so it can accept a dump load, so extended periods of low SOC will kill the battery
The splitting of the bank into two lowers total available capacity
The battery will not provide a constant load whilst in dump mode
Eventually you will get a time when the bank is full & you still need a second dump load
Excessive water used due to over charging
battery self discharge will be more of an issue if you have long periods of no charging the dump battery.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
billi
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« Reply #9 on: January 16, 2011, 01:16:20 PM »

Ok it is perhaps too much of an non calculable  experiment  ,  so perhaps back to my ancient  idea of using a DC pump and pump water in my stored hydro lake  Grin to harvest the energy later , but switching a pump constantly on is not good either  whistlie , or like clivejo says use my AC relay from the Inverter to charge a battery  or run a AC pump

 has anyone an idea where to get good Solid state relays  like this in Europe

http://www.power-io.com/library/databulletin/hdd-e-family.pdf

Billi
« Last Edit: January 16, 2011, 01:23:23 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
EccentricAnomaly
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« Reply #10 on: January 16, 2011, 01:56:39 PM »

need to keep bat SOC low so it can accept a dump load, so extended periods of low SOC will kill the battery

...if it's lead-acid.
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Justme
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« Reply #11 on: January 16, 2011, 02:01:33 PM »

need to keep bat SOC low so it can accept a dump load, so extended periods of low SOC will kill the battery

...if it's lead-acid.

True, but that is all that is affordable at this time.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
biff
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« Reply #12 on: January 16, 2011, 02:57:00 PM »

hi folks,
      before i set up my forklift battery bank i had a bank of 10 x 2 100ah 12 volt yousa, this was an exellent bank but i always thought i was abusing it when we used the washing machine,so thats really why i installed the forklift batts,
     my installation set up included a lever type fuse box that consisted of 3 x 20 amp fuses which pushed into place with considerable effort, lifting the lever knocked out the inverter which was connected to one end of all the fuses,the fuses themselves permenantly  connected the controller to the batteries,so having one fuse in place could have the forklift batts in use,then i push in the other fuse which connected up the yousa bank and then withdraw the fuse for the forklift bank, this way i could swop over the banks in seconds, this was a good way to keep the batteries charged up, leaving in the 2 fuses resulted in the forklift batteries pulling down the charge in the yousa because the yousa had a much higher voltage.
     its been a trouble free set up,apart from one forklift pack(72volt) running a bit dry,which was cured by a glorious tipple of rain water,the 48 volt pack was fine,a total teetotaler,,,,,,,,, so this is one way you could have a second batterybank.
                                                 biff
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An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
Outtasight
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« Reply #13 on: January 16, 2011, 05:07:38 PM »

I'm considering something for a secondary battery pack that can be run flat (NiMH or Lithium). 

I've got some old NiCad 4Ah cells (12V worth) that I might make up into a pack and use with a tiny 70W inverter for running just CFL lights on.  That would spare running the main 3kW inverter that draws 35W when idle!  NiCads don't mind running flat.  They actually need it to stop developing the memory effect.

I can also get 12V 4.5Ah NiMH laptop battery packs for my ancient Toshiba laptop very cheaply (25).  These have the thermistors built in for charge safety already so could be charged from a solar charger quite easily.
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3.58kWp & 800Ah LiFeYPO4 off-grid(ish). See 'Cobbled together PV in W.Sussex' (in "Show Us Yours")
Justme
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« Reply #14 on: January 16, 2011, 07:18:43 PM »


I've got some old NiCad 4Ah cells
I can also get 12V 4.5Ah NiMH laptop battery packs for my ancient Toshiba laptop very cheaply (25). 

Billi would need a fair few of them to use as a dump load for his 1600watt turbine.

Like 750 worth for the second hand laptop packs for just one hours worth of dumping or 1.6kWh.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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