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Author Topic: Upgrading from 48vDc to 120vDc, Pro's and Con's?  (Read 8038 times)
clockmanFR
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« on: August 10, 2013, 08:58:41 AM »

Presently at 48v with 1300ah batteries, (about 65Kwh).

Its sending the juice at 48v a couple of 100 meters so I am for ever installing very big cables to reduce cable losses.

My trackers are all sending max DC back to the MPPT controllers at 120vDc & 150vDc, so voltage drop is less.

Pros.
Could use a 120v Dc system to run most things directly around the house with out using an inverter.

Cons.
Internal resistance of batteries, is this a real problem?
Wiring at the power house will all need to be shielded like if Household mains supply, extra work.
Not many Inverters working at 120vDc in and 240vAc out. Name and model of Inverters?
Charging the batteries ?. need some controllers that will charge at 120vDc? or other solutions.

I like the principal of 120vDc but converting from 48vDc system?

If I was starting from scratch then 120vDc would be the way forward, but what about the appropriate equipment.

Biff runs a 120vDc system so I would be interested to see what he recommends.
 

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biff
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« Reply #1 on: August 10, 2013, 09:50:56 AM »

Good morning Clockman,
                           I am glad to hear you are considering changing over to 120vdc.On the question of inverters,The chinese 120v x 2kw inverter are still available and is not that expensive.There are three different types of 120vdc UPS,s available,ranging from 5.2kw to 2.7kw .They are not that expensive in fact they would be cheaper than the 48vdc version except for the Symmetra rm which I blether on about now and then.
   Then the controllers (all chinese) are relatively inexpensive compared to all the other big names I have heard discussed on Navitron.In all the times I have been using the digital chinese controllers,I have yet to see one of them pack up,so they are good.
    Charging the batts would have been my biggest concern and in the 6 years + that my system has been performing I have never once charged my batteries from a dedicated power source.I have depended entirely on the wind and solar and my reserve 48 system and them my final 800ah x 12 volt system which is very seldom used.I toyed with the idea of setting up an engine to power a 2kw wind turbine lump and using that to charge the batts.
  I have 2 x 2kw dump load immersions fitted to two tanks in our house but lately, because it has been so hot and Diese and Nat sleep by the front door in the hall,I have redirected all the dump load to our big D/H/W/C upstairs and watched the voltage creep up past the normal 140max .Remembering what Rogerico had said about the internal resistance of the batteries,I let it go the whole day in very bright sunshine.We got our tank heated to the max with the recirculating pump working away yet the voltage never passed 146vdc.I have of course got all my eggs in one basket here whereas normally there would be a dump load of 4kw or a second dump load to take the heat should one of the immersions fail but as an experiment,it was rather successfull.The downside is that you need a big battery bank yet you can fill it quicker and grab more energy while the going is good(compared to 48v of the same weight or ahs)Then of course the wiring is much less of a problem and the high voltage travels much better with the lower amps,I think my max amps would be around 20 amps approx.! 120 vdc works well enough on elictric fires and immersions but you would have to find out about anything else.I used to blether on about only having a diesel bill of 100 ltrs but this past years the diesel cans have stayed full and the generator has just lay there unused and overgrown.I think that this is the way that one should judge the success of any off-grid system.
                                                                       Biff
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biff
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« Reply #2 on: August 10, 2013, 10:06:18 AM »

In the early days when I set up the first bank,I was well aware of how dodgy 120vdc was under charge and it can arc so one has to be very carefull and just take more precautions than one would take with 220ac to be on the safe side.When I installed our forklift bank of 60 cells,i kept a further 10 x 100ah bank sitting ready in case I need to work on the forklift bank.Before working on the forklift bank,I would press a lever that connected the 100ah bank alongside the forklift bank and then pull the other lever which disconnected the forklift so that no charge would be going into the forklifts while I was in the area.This is about preventing a spark from igniting the gas so you would get that of any forklift bank maybe more so in 48vdc.
                                                                    Biff
                                   
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marcus
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« Reply #3 on: August 10, 2013, 11:03:25 AM »

Good call CM!

My tiny 24v bank is starting to show signs of age and I need something bigger anyway, but was wondering whether to go 'high' voltage or not.

the big 'cons' for me are:
the cost of a new 120v battery - the smallest Ah I've seen in traction batteries makes for a very big (for me) 120v battery.
my existing solar panels are only in matched sets for up to 48v  Sad.
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« Reply #4 on: August 10, 2013, 11:24:45 AM »

Hi Marcus,
           You need to check your vmps and see if they can be configured to any above 120volts and below 150 volts.
        I have a pair of panels with a vmp of 66v going into a 48bank successfully for the past 5years.really good job,these same one can be let loose on the forklift bank without the controller and they drop off about 58.9 volts.
   So you dont have to be absolutly spot on with the figures,however if you aim too low your batts will suffer,slightly high and your controller will redirect it to your water heaters.
  I am no expert,I am just going by what I see here in the ground.I have two 120volt arrays,a 48v array and a 12v array.The 24 volt one has been dismantled because I no longer need it.Its all brilliant stuff
                                                              Biff
               
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w0067814
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« Reply #5 on: August 10, 2013, 01:42:04 PM »

Remembering what Rogerico had said about the internal resistance of the batteries,I let it go the whole day in very bright sunshine.
                                                                       Biff

Biff,
Can you link to this for those of us with poor memories?

Thanks,
-Tim
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« Reply #6 on: August 10, 2013, 03:16:25 PM »

Seems like an awful lot of work to save on a few quids (or francs) worth of cable CM  Huh The sanity of switching 120v DC appliances in the house also seems questionable to me and I'm not particularly 'elfin safety' minded. Fine if you're starting from scratch but to convert a perfectly good 48v system after honing it for a couple of years  Huh Surely you must have better things to do  Grin

Without a doubt if you don't have to ever charge your batteries quickly with an external charger and are happy with UPS's or Chinese inverters then 120v is the way to go. However if you've spent all that time and effort developing what seems to be a reliable 48v system with dump loads and UFH I question your sanity  hysteria I'd be inclined to make some use of 'AC coupling' if you're worried about cable runs.

Good luck, Paul
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« Reply #7 on: August 10, 2013, 04:22:53 PM »

I'm sure it won't be cheap but how about the new TS-MPPT-600V from Morningstar when its released. I'd be interested in it but my battery bank is 48v and its only rated for 60A. (I don't quite understand why they rate it on current and not power).
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« Reply #8 on: August 10, 2013, 04:36:12 PM »

I'm sure it won't be cheap but how about the new TS-MPPT-600V from Morningstar when its released. I'd be interested in it but my battery bank is 48v and its only rated for 60A. (I don't quite understand why they rate it on current and not power).

I looked at that with interest, it is available now in the US but I think with a similar price tag to Xantrex's version, so around $1200 http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Xantrex-MPPT-Solar-Charge-Contollers/Xantrex-XW-MPPT-80A-Solar-Charge-Controller-up-to-600V-DC-input/p8992/  Shocked
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« Reply #9 on: August 10, 2013, 04:47:40 PM »

(I don't quite understand why they rate it on current and not power).

Because it's the current that creates the heat (in the circuit) and not the power  Huh

Just guessing  Grin
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« Reply #10 on: August 10, 2013, 05:07:59 PM »

Looking at the Morningstar data sheet, the power when into 120v battery bank is yet to be decided. Your link looks interesting but it only does up to 48v battery bank but does do 80A. Very expensive!!

With all these things their is so much flexibility.  I use a Trace inverter at the moment but I don't like to see the Morningstar MPPT on absorption when I could be using the wasted DC solar power for heating either the DHW, the buffer tank or the kids pool. That will finally change when I finally get the sunny backups installed, but then the batteries will be some distance away from the 'DC' PV panels.
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« Reply #11 on: August 10, 2013, 05:17:07 PM »

Right enough Tinbum,

http://www.morningstarcorp.com/en/support/library/TSMPPT600V-ds-Eng.pdf I'd forgot about that bit Supports nominal 48 or 120 Vdc batteries
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« Reply #12 on: August 10, 2013, 06:27:26 PM »

Hello again,
           I would agree,if your are happy with your 48volt system then thats fine but you can only do so much with a 48volt dump load.
     On the other hand,the 120vdc x 2kw chinese controllers come fitted with massive big resistors to act as dump loads,so all one has to do is bypass the big green resistors and direct it to the immersions.no call for mppt or anything like it.Add another array,great,,add another controller and bypass the resistors again in route to the second immersion,ect.There is no magic or board costing 500.00 to replace.The money involved in these controllers and inverters is much less expensive and a lot easier to understand and they are extremely reliable.
    mppt controllers are kind of risky.Thats the conclusion that I have come to.Once you fit the buxxers you cannot diddle about with them or you will upset them and bad things happen.
                                      Biff
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« Reply #13 on: August 10, 2013, 06:36:16 PM »

Hi Tinbum,
           If you go into the solar pv threads and look for "Solar pv direct to the battery,,temp"  by Rithym you will find Rogerico,s contribution on the subject,I have found the same thing happen in 48volt and 120volt. Its intresting.
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« Reply #14 on: August 10, 2013, 06:39:41 PM »


    mppt controllers are kind of risky
                                     

Can't argue with that Biff  Cool but there's nothing to stop you dumping AC with a decent inverter, it's what I do (have been for eight years) and you don't have the issues of switching DC. You cannot easily use a thermostat to control DC immersions like you can with AC. Horses for courses really.
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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
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