A recent post suggested that tapping into the middle of the a 12 or 24 volt battery was an acceptable idea in order to get 6 or 12 volts. A post previous to that was asking about doing something similar in an emergency. Such a tactic is definitely feasible from a technical standpoint. It is a very bad, bad idea for any long term use. If you need routine, long term power that does not match the voltages of the batteries that you have, the solution I would recommend is an ac to dc power supply, outputting the required voltage. This assumes that you have ac power available all the time. If you don't have ac all the time then you have a problem. But you could get a small inverter that will output ac from whatever dc voltage you have, then use the ac to dc power supply to get what you need. There is definitely some increased complexity involved, but is better than frying your batteries. And they will get fried. The ONLY argument is by how much they will get fried. Don't accept any assertion that this will not fry your batteries, unless it can be backed up with a reliable written/published study by a reputable researcher. Not only will it fry the battery not being tapped into, but the battery that is being used will not get fully charged and will sulfate and it too will die a premature death. The actual amount of damage is dependent on the level of amperage being drawn, the amount of time over which this is being done, the care with which the water levels are maintained and whether equalization is carried out routinely. You may be thinking, but what if the inverter/dc power supply system which has some complexity fails? Obviously, you use the emergency tap into the middle of the battery bank to get you home. But only as an emergency fall back. There is one more solution and that is to do the job right and put in a alternator running off the engine charging a battery of the correct voltage, supplying power at the correct voltage to the equipment that needs it. You can still use the tap into the middle of some other battery bank in an emergency. Mike Capt. Mike Maurice Wilsonville, Oregon (Portland).

Mike Maurice wrote: >If you need routine, long term power that does not match the voltages of >the batteries that you have, the solution I would recommend is an ac to dc >power supply, outputting the required voltage. This assumes that you have >ac power available all the time. If you don't have ac all the time then >you have a problem. The other solution is a DC-DC converter. On my boat the 24 volt house bank is reduced to 12 volts for equipment that cares, such as the VHF radios and other electronics. A side effect of this is some very well-regulated power -- it is always 13.7 volts. Newmar makes these, they are not cheap, I know because I had to replace the one that came with the boat and died on its maiden (for me) voyage :( Best, Steve >But you could get a small inverter that will output ac from whatever dc >voltage you have, then use the ac to dc power supply to get what you need. >There is definitely some increased complexity involved, but is better than >frying your batteries. And they will get fried. The ONLY argument is by >how much they will get fried. > >Don't accept any assertion that this will not fry your batteries, unless >it can be backed up with a reliable written/published study by a reputable >researcher. > >Not only will it fry the battery not being tapped into, but the battery >that is being used will not get fully charged and will sulfate and it too >will die a premature death. The actual amount of damage is dependent on >the level of amperage being drawn, the amount of time over which this is >being done, the care with which the water levels are maintained and >whether equalization is carried out routinely. > >You may be thinking, but what if the inverter/dc power supply system which >has some complexity fails? Obviously, you use the emergency tap into the >middle of the battery bank to get you home. But only as an emergency fall back. > >There is one more solution and that is to do the job right and put in a >alternator running off the engine charging a battery of the correct >voltage, supplying power at the correct voltage to the equipment that >needs it. You can still use the tap into the middle of some other battery >bank in an emergency. > >Mike > > >Capt. Mike Maurice >Wilsonville, Oregon (Portland). >_______________________________________________ >http://lists.samurai.com/mailman/listinfo/trawler-world-list > >To Unsubscribe send email to trawler-world-list-request@lists.samurai.com >Include the word "Unsubscribe" (and nothing else) in the subject or body >of the message. > > > ---------------------------------------------------------------- Steven Dubnoff sdubnoff@circlesys.com Circle Systems We make your data instantly usable. Download Stat/Transfer from http://www.stattransfer.com 1001 Fourth Avenue, #3200 (206) 682-3783 Seattle, WA 98154 Fax (206) 328-4788

Friday, February 13, 2004, 9:44:40 AM, Mike wrote: > A recent post suggested that tapping into the middle of the a 12 or 24 volt > battery was an acceptable idea in order to get 6 or 12 volts. A post > previous to that was asking about doing something similar in an emergency. > Such a tactic is definitely feasible from a technical standpoint. It is a > very bad, bad idea for any long term use. I agree that tapping a battery (or group of batteries) to get a lower voltage is a Bad Thing for long term use, but for "emergency" use, it should be OK (the OP's proposal was for occasional use as "emergency starting") > If you need routine, long term power that does not match the voltages of > the batteries that you have, the solution I would recommend is an ac to dc > power supply, outputting the required voltage. DC-DC converters are available - I understand long-haul truckers often use a 24V in. 12V out DC->DC converter to allow use of "normal" DC accessories in a 24 volt truck. Newark Electronics and Digikey should carry a variety of DC->DC converters, in various combinations of input and output voltages (and power ratings) -- Peter Bennett, VE7CEI Vancouver, B.C., Canada GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver-webpages.com/van-ps