charging a second battery bank , with dump load from a pmw
cockneybob2
Registered Users Posts: 18 ✭✭
hi all , electronics are new to me so if I make myself sound foolish please bare with me , I just need help and advise .
this will be a small setup , about 500 ah at 24 volts with solar with a mppt and wind with a mpw charging the main battery bank , if the sun and wind was working to their max about 2 kw would be produced so I want to use the dump load to the max , so can I do is and will it work safely ????????????????
when the main battery bank is full but power is still in abundance , feed the dump load cable through a relay driver ( which I think turns it back into DC power? ) then straight into a second battery bank and inverter , this inverter would power say a 240 volt air con units or fan heaters , when the battery bank got to a set discharge level , they would just turn off safely , there will be resistors , in case for what ever reason they is no load .
hope that all made sense to you
many thanks
robert
Comments
AC or heating would be more of an "opportunity" load which you might optionally use with good output and full batteries. You may not want heat/AC as an automatic, non-optional dump load though.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
Basically, wind power stays connected to battery #1 at all times. If your battery #1 is full then the controller #1 is connecting a load/resistors #1 to the battery #1 while your wind power stays connected. This will draw power from battery #1.
Your load/resistors #1 could be a battery or let's call it battery # 2. If battery # 2 gets full you need a controller #2 to dump power into your resistors to avoid over charging battery # 2.
If using a inverter at any battery then a low voltage shut off should be incorporated, since most inverters will shut down when the voltage is way to low and when the battery is discharged or dead which kills batteries in no time.
Depending, you may need to control the amps into battery #2. You may even need a charger or generator to fully charge battery #2.
I would make battery #1 bigger and not using battery #2 , dump power into a water heater with controller #1.
When water heater is turning off, controller #2 can dump power into the resistors or a heater in winter.
|| 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 ,
When the thermostat goes off a second controller can dump that extra power into a resistor.
If the battery need to be disconnected at a point for maintenance for example, there should be a switch installed that will short circuit the 3 phase ac side at the rectifier, this will put a load on the turbine and act as a break.
hi guys , thanks for your comments , the reason I would like to channel the diversion mode / dump load power from the PWM charge controller into another battery is to use the excess power to run , lets call them self indulgent mains AC appliances , instead of just burnt off by water heaters or resistors .
I want to put as little strain on the main battery bank as possible , to get the max life span out of it , I would never try and run those appliances from the main bank as it would mean monitoring all the time so the % of it didn't drop to low , I do not want to be switching things on and off all the time .
the impression I get is that I can put the dump load into another battery ( is that correct ) ? if so , I believe the power from the dump load is pulse not pure DC , which is ok for resisters and DC water heaters but is it ok to put straight into a second battery or does in need to be cleaned / smooth through a relay driver ? .
you said the second battery bank could have its own PWM charge controller so it can dump load into a resister , great idea thank you , this inverter would be set to a high % stop voltage , say 95% so never really runs down to far , the idea being , the appliances would only run when there was excess power .
please let me know if this can work , its driving me mad .
many thanks Robert
However, I dislike complexity of design in systems that are supposed to work for years with little maintenance. You would need at least two charge controllers on bank "A". One to move current to battery bank "B", and a second controller to dump excess energy from "A" to a resister bank when "B" is full. And, you really should have a backup dump controller+load on "A" in the case if both dump controllers/loads fail.
Second--If you do not have enough energy--Battery bank "B" will be the first to suffer--Needing you to use a backup genset and/or you will need to manually manage loads on bank "B" (and "A"?) to ensure that you do not kill either bank.
Dump controllers are not as good at regulating battery bank state of charge--You either are dumping charging current into the bank or dumping load. With series (standard configuration) solar charge controllers, you are either charging or "off"--This is better.
Now--Normally, in a system with a solar array, you would have a series charge controller for the solar array regulation, and a second (one or a pair) of dump controllers setup as dump controller(s) to regulate the wind turbine charging (the solar controller would be set, for example, to charge to 14.6 volts, and the dump controller set to charge to 14.8 volts. Wind turbines typically do not have predictable/daily charging unlike solar. Gives you the advantage of better charging controller with the series type solar charge controller and the dump controller to control over charging when needed during stormy weather/windy season). That is another charge controller (with PWM controllers, you can share one solar array with two PWM charge controllers to separate battery banks).
I would suggest that you simply have one battery bank / charging setup (solar+wind)--And simply mange your secondary loads (turn them off when poor charging conditions are present--or when the battery bank is at a lower state of charge).
Things fail--And they can fail in different ways. A failure of a series charge controller will stop charging your battery bank (not good for the battery). A failed dump controller (or dump load) will over charge the battery bank and can run the risk of fire. (note: series charge controllers have been known to fail and over charge batteries too, just that failing shorted seems to be less common).
I believe that a single battery bank will be much easier to maintain, debug, and safer than a "master/slave" battery bank setup.
-Bill
thanks bill , lot to take in , back to the drawing board I think
many thanks for the advise
robert
Use an MPPT type charge controller to take the higher voltage battery and down convert to the 12 volt battery. However--As you can tell, this discharges the main battery bank in favor of the lower voltage battery bank--So you still have to monitor your loads.
By the way, how well is the wind turbine working for you? In general, most installations do not seem to reliably generate much useful power. There are a few people that have done well, but most build their own turbines on put them on 60-90 foot towers.
From a person that ran a Skystream turbine for a few years (grid tied--So this is the "best" harvest that you will get--Battery charging always "tosses" some energy away when the batteries are full and you do not have enough loads--Note that the Skystreams did seem to be the best producing "small" wind turbines--When they worked):
* December, 2007 - Skystream shut down from software problem with cold and would not restart.
* January, 2008 - Skystream down until the 27th. Produce 98kWh in the 5 days remaining in the month.
* December, 2009 - Skystream shut down several times and would not restart on it's own, production very low for wind speeds.
Seems to have worked.
Remember that this was from a customer that had heavy support from the vendor (Skystream, now out of business). Was unhappy, complained, got support, was then "happy".
-Bill
https://web.archive.org/web/20100603163140/http://blog.keepturning.com/2008/02/11/janes-household-skystream-kwh-record.aspx
For most people, I would suggest solar panels is a better/lower maintenance/cost system... However, if you are in Peterborough, EN, United Kingdom area--You probably don't get much winter sun (fixed array, 45 degrees):
http://pvwatts.nrel.gov/pvwatts.php
3 hours of sun per day of sun is pretty reasonable. 1 hour of sun per day--Not great.
-Bill
hi bill , thanks again for your incredible detailed and knowledgeable input / comments .
I am only at the planning stage of a boat fit out in the near future , I think I got a little carried away with myself and the expectations of what a solar and wind system can and will produce .
the idea was to use the free / excess power but now looking at the reality of it all , it would never be free due to the high setup costs , for something at best would only happen once in a blue moon so it doesn't make sense .
one battery bank and monitoring the input power , then using appliances where applicable is the prudent and sensible way forward .
like a lot of thinks and ideas in life , are start with good intentions but then find out that in fact has no merit .
once again , thank you for your input , it has been invaluable .
regards
Robert
If you have a spare battery and are willing to manually shuffle batteries around, this same technique could be used to make sure that each battery in a string gets a full charge every two weeks. Discharge it to match the batteries in the string before putting it back into the string.
Of course using a generator is easier....
I am available for custom hardware/firmware development