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| Pvusers Archive for January 2002 |
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| 102 messages, last added Tue Nov 26 17:28:41 2002 |
[Date Index][Thread Index]
Re: [pvusers] Dual voltage systems mind teaser
Jeff,
We've had some trouble in the past with some of the high frequency switching
supplies being able to surge without drooping, especially with A3j analog
modes and some of the digital modes like AMTOR, PACKET, and PK31. Human
ears don't mind the distortion on modes like CW, but computers haven't
figured out auto-compensation yet ;-)
One of the tricks we have done is to add a large electrolytic capacitor on
the output of the regulators that are slow to surge. They aren't cheap,
especially for 15K-30K UF @ 25 volts, but they do the job well. You have to
charge them up slowly as some regulator power supplies will crowbar in the
initial surge and have to watch accidental shorts carefully else you become
instant experts at DC welding ;-)
Ultimately this is looking like it will require one large set of 24v DC
wires (able to handle all office DC loads possible) from the main breaker
out 25 feet to the office sub-breaker, then bussed out to individual
regulators, each pre-tuned to their required voltages (12 for answering
machine, nicad charger & cell phone, 13.8 for radio's and amps) and large
capacitors on the bigger beasts like the 400 watt VHF amp for weak signal
long distance work. In the grand scheme on things, only one of the smaller
regulators will be on 24 hours a day, with the others used as needed.
I won't even worry about the 42 volt automotive standard for a while,
although there should be a lot of side benefit from it.
I was considering going 48 volts with the house system initially, but the
Xantrex Trace SW4048 inverter emits a large amount of EMI due to its stepped
sinewave. The harmonics of those squares edges are detectable well over 100
feet away with sensitive HF and VHF equipment. I have not detected any such
EMI from the Prosine inverter, however they do not make a 48 volt DC model
that I know of. I do not have enough data yet to know whether Vanner or
Exeltech would be good choices for us yet. I've have some time yet for
investigation and will focus on it at the MREA energy fair this June. At
this point we are sticking with 24 volts for the Prosine 3KW inverter until
I think differently. We are probably going to install the Maytag 1956 18.5
cu ft refrigerator and our booster pump is available in 24 or 48 volt DC.
I'll have to rethink the Rolls batteries too if changing from 24 to 48 volts
DC.
Thanks,
Dave
----- Original Message -----
From: "Jeff Clearwater" <clrwater@earthlink.net>
To: "David & Sheila Knapp" <solar@aeroinc.net>
Cc: <pvusers@crest.org>
Sent: Sunday, January 20, 2002 12:52 AM
Subject: 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
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