 |
 |
|
 |
 |
 |
 |
 |
 |
 |
 |
| |
REPP-CREST
1612 K Street, NW
Suite 202
Washington, DC 20006
contact us
|
|
 |
|
|
|
|
| Pvusers Archive for January 2002 |
|
| 102 messages, last added Tue Nov 26 17:28:41 2002 |
[Date Index][Thread Index]
Re: [pvusers] Dual voltage systems mind teaser
Hi Dave and Sheila and all,
In which case Cor's reply is right on the money. Sevcon, Vicor,
Curtis, and others make 30 amp DC>DC converters with often adjustable
output voltages in the range you need. They are often in the upper
90 % efficiency levels and highly reliable. Much better than two
packs and trying to keep one at charge voltages all the time. Just
use what you need when you need it.
And yes there's the coming 42 volt automotive standard.
Unfortunately DC>DC converters are usually only efficient in a down
voltage conversion (I hope I'm wrong on this, but I fear not - what
do ya say electronics heads out there?) so if you commit to 24 volts
now and then do have a need to run alot of 42 volt equipment in the
future, you may want to go to 48 volt battery pack now. There are
several 48 > 12 VDC converters available. 48 volt systems have the
advantage of smaller wire and cable sizes. The disadvantage comes in
having to have 48 Volt increments of batteries and inputs (like PVs
in 4's and wind gennies in 48 volts etc.)
So explore the DC>DC converter world. I think you'll find your solution there.
Hope that helps,
jc
At 12:01 AM +0100 1/20/02, Cor van de Water wrote:
>You say, you need 20 Amp+ so this is 240W+ and not a big deal for a
>good DC/DC converter.
>
>I suggest you forget the 12V battery and all the headaches that come
>with installing a dual voltage battery system; Wire your house and
>shack for 24V and have a good DC/DC converter (or two) supplying the
>12V when you need it. When your leave the shack; simply turn off the
>converter if the 12V is not needed any more (unless for a phone, thats
>why you may go for 2 converters)
>Jeff,
>
>That would seem to be the simplest solution if most of the equipment worked
>well at 12.6 volt or lower during surges of withdrawal form the house. I
>need 13.8 volts. Also, larger wires would have to be brought out to handle
>the very low voltage drop we'd need for the distance they would travel.
>
>The automotive/RV industry isn't making it easier either. In a few years
>cars & RV will be going with the new 42 volt standard to handle all of the
>gadgets cars are getting now. They avoided the 48 volt standard because of
>OSHA and NEC limits, but their 42 volt standard is not standard with many
>others unfortunately.
>
>;-)
>
>Dave
>
>----- Original Message -----
>From: "Jeff Clearwater" <clrwater@earthlink.net>
>To: <pvusers@crest.org>
>Cc: "David & Sheila Knapp" <solar@aeroinc.net>
>Sent: Saturday, January 19, 2002 5:55 PM
>Subject: Re: [pvusers] Dual voltage systems mind teaser
>
>
>> Hi David and Sheila,
>>
>> Have you considered just using one solid 24 volt pack sized to do all
>> the loads and then using a Vanner battery equalizer? The unit does
>> what you have talked about doing with a MPPT controller charging the
>> second pack, but this way you get to utilize all the AHs available
>> for all the loads and your voltage will stay higher throughout the
>> cycle. You also get to use all your inputs for all loads rather than
>> have some PV dedicated and therefore potentially underutilized.
>>
>> The Vanner is basically a DC>DC converter that constantly monitors 12
>> volt both halves of a 24 volt pack and uses the 24 volt tap to charge
>> either of the 12 volts taps as needed, constantly keeping the two
>> halves balanced. They cost about $350, are built very solid and work
>> for a long time hassle free. It's the best solution I've found for
>> dual voltage needs.
>>
>> Hope that helps,
>>
>> Jeff Clearwater
>> Ecovillage Design Associates
>>
>> >Originally we had specified two separate systems for our new solar home.
>The
>> >main house system would be 24 volts nominal and the office/ham radio
>system
>> >would be 12 volts nominal.
>> >
>> >I specified the main house system to be 24 volt because the daily load is
>> >about 3,000 W-H. The separate office/ham radio system came about because
>we
>> >have quite a few devices that consume 12 volt nominal power much more
> > >efficiently that using an AC power supply to convert back to low voltage
>DC.
>> >
>> >Although the ham radios run off of what is called 12 volts, their best
>> >efficiency and ultimate happiness rests with running them at 13.5 - 13.8
>> >volts (a vehicles charging voltage). Several other appliances including
>our
>> >cell phone charger, answering machine, DC charger (AAA, AA, C, D cells,
>> >etc.), and a citizen's band radio for the local emergency network runs
>well
>> >from it too.
>> >
>> >Initially I specified 300 watts of PV and 415 A-H of sealed batteries at
>12
>> >volts for the office system. The main house system would use ~1500 watts
>of
>> >PV and a large bank of Rolls batteries located in the utility area of our
>> >solar earthship. The smaller 12 volt nominal office system with the
>sealed
>> >batteries would be located close to the ham radios in a Rubbermaid
>container
>> >for a minimum voltage drop.
>> >
>> >It seemed like a workable solution until I examined the charging cycle
>over
>> >a 24 hour period. The 12 volt nominal system would use MPPT charging to
>> >bring the sealed batteries up to 13.8 volts during the day when the sun
>was
>> >shinning and allow it to drop to resting voltage at night. Most of the
>> >constant loads were small, but did add up over 24 hours. The larger
>loads
>> >from the ham radios (up to three hundred watts on transmit) could
>potential
>> >bring the battery voltage below 12.0 volts at night when the radios would
>be
>> >used the most when the charging would already be finished for the day.
>> >Although the battery voltage would come back up after each transmit
>cycle,
>> >the radios are not very happy working down there. They much prefer the
>> >automotive standard of 13.5 volts. I have heard many backwoods radios
>emit
>> >distortion when running from an RV battery during extended operation as
>the
>> >battery voltage sagged. Even during the day, the peak charging is only
>~13
>> >amps (plus any MPPT boost). The ham radios draw 20 amps on transmit plus
>the
>> >smaller constant loads. I briefly considered using AC power supplies for
>> >the larger radios, but did not want to add an extra inverter and was
>> >bothered by the efficiency loss of so many power conversions.
>> >
>> >I then considered using AC from the main house inverter, but then I knew
>I
>> >was stealing power away from the house system and letting it go to
>'waste'
>> >in the office system. Then an idea was born, why not combine the two
>> >systems into one bigger system.
>> >
>> >The new design called for 1800 watts of PV wired up for the main 24 volt
>> >nominal system in two array's feeding a couple of MPPT charge controllers
>to
>> >a Roll's 1,900 A-H battery bank. There are a several 24 volt nominal DC
>> >loads (booster pump, emergency DC lighting, refrigerator, etc.), but the
>> >majority of the DC loads are for the office and require 12 volts nominal.
>> >
>> >I had the idea of using another MPPT charge controller to convert the 24
>> >volt nominal to 12 volt nominal and to use a small 210 A-H 12 volt
>battery
>> >bank as a buffer. It would do this at 97% efficiency and I could
>precisely
>> >control the output voltage 24 hours a day as long as I stayed under the
>50
>> >amp limit of the charge controller (which was no problem).
>> >
>> >The big problem I have run into so far is have both systems grounded to
>the
>> >same point. This arises from the negative wires on both systems being
>> >grounded as required by code. This effectively messes up the function of
>> >the MPPT controller in the office system which requires an isolated
>input.
>> >The ham radio system has to be negative grounded as all of their chassis
>> >connections are connected to the negative wire as also are all antenna
>> >shield connections and all antennas. Even using a Trimetric meter with
>an
>> >external shunt to monitor the charge status of the office battery system
>> >won't work if I understand its operation properly.
>> >
>> >The NEC as adopted in Colorado requires a ground on all current carrying
>> >wires that aren't fused, yet one side must be grounded if I understand
>the
>> >NEC code properly. Further, by having a common negative ground as I
> > >described it, I have set up the potential where the ground could carry
>the
>> >current intended for the negative wire because of the loop I had now
>formed.
>> >Changing the MPPT controller to a voltage regulator (24 to 12 volts)
>seems
>> >to not change anything unless I go to a regulator that has a common
>negative
>> >for both input and output. At that point, using a shunt on the buffer
>> >battery appears to suddenly seem like that it will work okay. It is only
>in
>> >the controllers that require an isolated input that dual voltage systems
>get
>> >into trouble.
>> >
>> >I am only giving up some efficiency in the charge regulator of the
>> >unisolated input negative type unless I can find a higher quality one
>that
>> >is using high frequency DC switching. It looks like the mechanics of it
>will
>> >work, now I just have to convince the CO state code inspector that the
>> >smaller ham radio system subset is a legal system with regards to being
>able
>> >to shutdown the main system and the second smaller system having it's own
>> >battery disconnects (as well as the 24 volt breaker feed at the main
>> >system). It is impossible and impractical to install it all right at the
>> >main system within six feet of each other as the office system is some 25
>> >feet away located right at the point of use.
>> >
>> >Once I resolve all of these issues, I'll have to document it. I cannot
>> >believe there already has not been an article in HP about similar
>> >circumstances such as these. As more people mainstream into RE, it is
>> >likely that this will be encountered again and again. A non-gadget guru
>> >would not understand the problems they would face in this scenario. Even
>> >several dealers called it unusual as well as the MPPT charge controller
>> >manufacturer who suggested we simply leave the 24 volt system ungrounded,
>> >which I am not about to violate code or go to the expense of adding dual
>> >breakers for all 24 volt negative and positive wires in a system that
>daily
>> >consumes 3+ KWh. I'm sure there are some wrenches out there that might
>have
>> >solved a problem or two like this and still kept the code inspector
>happy.
>> >
>> >;-)
>> >
>> >Dave Knapp
>> >http://www.esolarliving.com
>> >
>> >
>> >
>> >
>> >--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*
>> > List sponsored by CREST/REPP
>> > http://solstice.crest.org/ http://www.repp.org/
>>
>> --
>> ~~~~~~~~~~~~~~~~~~~
>> Jeff Clearwater
>> Ecovillage Design Associates
>> 2525 Arapahoe Ave, Suite E4, #280
>> Boulder, CO 80302
>> Community and Village Scale Renewable Energy Systems
>> 303-546-0460, clrwater@earthlink.net
>>
>> Council Member - Ecovillage Network of the Americas
>http://www.ecovillage.org
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*
>> List sponsored by CREST/REPP
>> http://solstice.crest.org/ http://www.repp.org/
>>
>
>
>
>--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*
> List sponsored by CREST/REPP
> http://solstice.crest.org/ http://www.repp.org/
--
~~~~~~~~~~~~~~~~~~~
Jeff Clearwater
Ecovillage Design Associates
2525 Arapahoe Ave, Suite E4, #280
Boulder, CO 80302
Community and Village Scale Renewable Energy Systems
303-546-0460, clrwater@earthlink.net
Council Member - Ecovillage Network of the Americas http://www.ecovillage.org
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*
List sponsored by CREST/REPP
http://solstice.crest.org/ http://www.repp.org/
|
|
|
