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How to decide on a system voltage? | 14 comments (14 topical, editorial)
Re: How to decide on a system voltage? (3.00 / 0) (#9)
by PaulJ on Sun Aug 10th, 2008 at 05:41:07 AM MST
(User Info)

   Given the amount of 12V gear you already have, and the fact that you really only need backup power when the grid goes, I'd say stick with the 12V.

   A couple of warnings:

   1)  "12V" can be up to 15V when equalizing flooded batteries- make sure your 12V gear can cope with/is protected from this.

   2)  The fridge complicates things a bit, a full size domestic fridge is probably close to the limit (but not out of the question) for a 12V system.
    My new efficient fridge also uses 110W running, but its startup surge is over 2kW for half a second or so. You'll need an inverter with that sort of surge rating as a minimum to start just about any fridge reliably.
 Also, a sinewave inverter will run a fridge more efficiently than a cheaper MSW inverter.

   Paul.



Re: How to decide on a system voltage? (3.00 / 0) (#10)
by la7qz on Sun Aug 10th, 2008 at 08:06:48 AM MST
(User Info) http://home.no.net/naomij

Hi

Ham gear is generally designed to operate on 13.8V and many transcievers will start FM-ing at anything below 12V. To protect your ham gear when battery voltage is high (equalizing) AND give it a good operating voltage when the batteries are low, you might want to look at the MFJ-4416 battery booster.

I installed one on my boat to make sure I have communications in an emergency even if my battery voltage is dropping (from running the bilge pumps or other reasons), but I find that it is also an excellent solution for keeping my Kenwood TS-570D at top performance at times when the batteries are not fully charged. After all, the only time they are near 13.8V or above is when the batteries are well charged and have an active charging source (solar, wind or diesel engine).

The only problem with the MFJ-4416 is that at max 25A, the capacity is a little too low when you want to add other gear in addition to your transceiver. The internal 30A fuse blew once when I was testing the transmission at 100W with a low battery. I assume the drain from the battery was more than 30A when the low battery voltage needed to be boosted to 13.8V. In future, I will reduce my power if I need to transmit when the batteries are low. Another point is that I make my living as a marine electrician. One of my specialities is marine SSB installations. Most marine SSB radios are 150W, so the capacity of the MFJ is too low for these installations.

The manual is here:
http://www.mfjenterprises.com/man/pdf/MFJ-4416.pdf

PS.I do not like the idea of the RF sensing circuit in the MFJ and don't use it. It would also be a bit difficult for me to implement since the Kenwood has two antenna connectors and I use both for two different antennas. (a longwire with SG-230 antenna coupler and a 14MHz vertical dipole) The unit is installed between the circuit breakers for the ham gear and the radio, so I simply switch it off at the breaker when I'm not using the radio.

PPS. Usual disclaimer. I do not sell MFJ equipment, I just use it and occasionally install for my customers.

PPPS. You'll often find me on the Maritime Mobile net on 14297.5 at 1900z on Saturdays and Sundays and also occationally on the MMSN at 14300 a bit later in the evening.

Owen

If you're not living on the edge, you're taking up too much space.
[ Parent ]



Re: How to decide on a system voltage? (3.00 / 0) (#11)
by RandomJoe on Sun Aug 10th, 2008 at 10:38:05 AM MST
(User Info)

I found out about the fridge this morning!  I guess I'd been lucky with the other motor-driven things I've tried to run off generator or inverter.  Up til now I'd only had one thing (9000 BTU mini-split A/C) that I couldn't get to start on the generator.  Interestingly, the 9000 BTU portable A/C unit does start and run just fine on it.  (The first time I had it on generator, I thought just the blower was running, kept waiting for the compressor to kick in.  Then realized it was blowing cold air!)

But I tried running the fridge with a 300W (600W surge) Samlex pure-sine inverter, and no joy!  The inverter made some noise, I saw a 100W draw, but nothing from the fridge then a few seconds later the inverter tripped.  My Kill-A-Watt isn't quick enough to catch that surge, of course, so had never shown it.  

I knew motor inrush could be pretty substantial (I work with 460V 3-phase stuff for a living) but had always heard 3x running, or maybe as high as 6x running.  2kW, though, for a fridge...  Wow!

I hadn't thought about the equalizing voltage yet.  Up to now I've only used SLAs, so it hasn't been an issue.  I may just turn off / disconnect everything during equalization, or switch over to the PSU.  The MFJ conditioner is another good idea, been thinking about getting one of those anyway for portable use.

[ Parent ]



Re: How to decide on a system voltage? (3.00 / 0) (#12)
by Jeff (ruralmcguyver at yahoo dot com) on Sun Aug 10th, 2008 at 11:18:13 AM MST
(User Info)

I have a 1200watt/3200peak MSW inverter & it starts my fridge with no problems. I have found a couple decent kits that will reduce the startup problems for those that need it. They might even decrease the load on the batteries enough that it saves some power.

http://www.azpartsmaster.com/Products/Compressor-Hard-Start-Capacitor---SUPCO-RSC10_SPP10.aspx

http://www.filterace.com/detail.aspx?ID=1112
Rural McG
[ Parent ]



How to decide on a system voltage? | 14 comments (14 topical, 0 editorial)

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