Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
Al, Your point is well taken and I understood this. However, for the most part a rig is not going to be drawing much current, in receive most of the time. Little affect on the charge/discharge of the lower battery. This is why in a previous post I said depends on the load if wanting to connect across the lower battery. I think the solution to this topic came from you and others long ago. Use a 24-12 converter. They are about the same price as a battery. However, for the typical 50 W rig I would have no problem connecting across the bottom battery. The batteries get lots more abuse from the vehicle. A 1 amp draw 99% of the time is little compared to the typical draw from the other stuff. If drawing the currents you are talking about, again connecting to the lower battery would be a problem. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] Date: 2008/03/29 Sat AM 01:07:34 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc Ron, et al, A corollary of Kirchhoff's law says that all currents are equal in a series circuit and all voltages are equal in a parallel circuit. Tapping a load across the lower battery represents a parallel circuit of the bottom battery and the load (radio) using 12 volts, and this parallel circuit is in series with the upper battery. If I supply 10 amps from the 24 volt charging circuit the upper battery receives 10 amps. However, if the load (radio) draws 5 amps the bottom battery can only get the other 5 amps to charge it. Hence the application of Kirchhoff's law of currents equal in a series circuit. There is no way for the bottom battery ever to be equally charged with the top battery as the radio has drawn away some of the current from the bottom battery. This current can never be replaced in this configuration. If the charging current drops to 5 amps then the top battery get 5 amps and the bottom battery gets none. If the charging device is off then the bottom battery continues to supply 5 amps to the load (for a while!) If this condition continues very long the terminal voltage of the bottom battery will be depressed towards 12 volts or lower but the 24 volt charging device doesn't know this and will attempt to apply full charging voltage (probably 28 volts or so) to the two seriesed batteries. If the depressed voltage on the bottom battery is down to 12 volts (typical) the top battery will get 16 volts, not a healthy situation! It only get worse as the condition continues. Now there are solutions. One can switch batteries (top with bottom) every few hours but who would actually do this? Or one could put a phantom load across the top battery, something that draws about the same current as the radio but this would be rather wasteful of energy and tricky to make work. Many 12 to 14 volt linear power supply circuits (Astron or ARRL handbook) can be adapted to convert the 24 - 28 volt source down to 12 - 14 volts just by injecting the +24 volts into the power supply after the main rectifier diodes. But here again the power supply will use up about as much power as the load. (Kirchhoff's law again) If conserving power is important then a switching supply would be in order as some of them are more than 90 % efficient. 73, Al, K9SI Re: 24 vdc to 12 vdc Posted by: Ron Wright [EMAIL PROTECTED] n9eerptr Date: Tue Mar 25, 2008 5:04 am ((PDT)) Depending on the load connecting across one battery, the one connected to ground or the lower of the 2 12 batteries, will work. I would not do is load is heavy because I am sure the charging system is for both batteries and draining one much more than the other could upset things. Kirchhoff's current law says the sum of the currents will be zero. Kirchhoff's voltage law says sum of voltages will be zero. Not sure why revelant here, but I am sure Kirchhoff had something else to do with voltage and current sources. Would like to know. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] Date: 2008/03/24 Mon PM 04:36:54 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc This is a very common issue in aircraft. The most obvious question is does your jeep use 2 each 12 volt batteries? If so, simply connect your radio across one of 'em. This is done all the time but is a very, very bad idea. Ever hear of Kirchhoff'wbrs law? Check it out. It's a very quick way to ruin two batteries. Get a real converter. The switching kind are much more efficient than the linear voltage dropping kind. Al, K9SI Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: [Repeater-Builder] Re: 24 vdc to 12 vdc
Ron and All, EZGO Golf Carts do this all the time with there electric golf carts, they tie the tail lights and head light if any to the lower two 6 volt set of batteries. I admit it is not the best way to go about it but it seems to work, as Ron said, it depends on the load and in the case of the carts the duty cycle. Paul -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Saturday, March 29, 2008 5:22 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: 24 vdc to 12 vdc Al, Your point is well taken and I understood this. However, for the most part a rig is not going to be drawing much current, in receive most of the time. Little affect on the charge/discharge of the lower battery. This is why in a previous post I said depends on the load if wanting to connect across the lower battery. I think the solution to this topic came from you and others long ago. Use a 24-12 converter. They are about the same price as a battery. However, for the typical 50 W rig I would have no problem connecting across the bottom battery. The batteries get lots more abuse from the vehicle. A 1 amp draw 99% of the time is little compared to the typical draw from the other stuff. If drawing the currents you are talking about, again connecting to the lower battery would be a problem. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] Date: 2008/03/29 Sat AM 01:07:34 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc Ron, et al, A corollary of Kirchhoff's law says that all currents are equal in a series circuit and all voltages are equal in a parallel circuit. Tapping a load across the lower battery represents a parallel circuit of the bottom battery and the load (radio) using 12 volts, and this parallel circuit is in series with the upper battery. If I supply 10 amps from the 24 volt charging circuit the upper battery receives 10 amps. However, if the load (radio) draws 5 amps the bottom battery can only get the other 5 amps to charge it. Hence the application of Kirchhoff's law of currents equal in a series circuit. There is no way for the bottom battery ever to be equally charged with the top battery as the radio has drawn away some of the current from the bottom battery. This current can never be replaced in this configuration. If the charging current drops to 5 amps then the top battery get 5 amps and the bottom battery gets none. If the charging device is off then the bottom battery continues to supply 5 amps to the load (for a while!) If this condition continues very long the terminal voltage of the bottom battery will be depressed towards 12 volts or lower but the 24 volt charging device doesn't know this and will attempt to apply full charging voltage (probably 28 volts or so) to the two seriesed batteries. If the depressed voltage on the bottom battery is down to 12 volts (typical) the top battery will get 16 volts, not a healthy situation! It only get worse as the condition continues. Now there are solutions. One can switch batteries (top with bottom) every few hours but who would actually do this? Or one could put a phantom load across the top battery, something that draws about the same current as the radio but this would be rather wasteful of energy and tricky to make work. Many 12 to 14 volt linear power supply circuits (Astron or ARRL handbook) can be adapted to convert the 24 - 28 volt source down to 12 - 14 volts just by injecting the +24 volts into the power supply after the main rectifier diodes. But here again the power supply will use up about as much power as the load. (Kirchhoff's law again) If conserving power is important then a switching supply would be in order as some of them are more than 90 % efficient. 73, Al, K9SI Re: 24 vdc to 12 vdc Posted by: Ron Wright [EMAIL PROTECTED] n9eerptr Date: Tue Mar 25, 2008 5:04 am ((PDT)) Depending on the load connecting across one battery, the one connected to ground or the lower of the 2 12 batteries, will work. I would not do is load is heavy because I am sure the charging system is for both batteries and draining one much more than the other could upset things. Kirchhoff's current law says the sum of the currents will be zero. Kirchhoff's voltage law says sum of voltages will be zero. Not sure why revelant here, but I am sure Kirchhoff had something else to do with voltage and current sources. Would like to know. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] Date: 2008/03/24 Mon PM 04:36:54 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc This is a very common issue in aircraft. The most obvious question is does your jeep use 2 each 12 volt batteries? If so, simply connect your radio across one of 'em. This is done all the time but is a very, very bad idea. Ever hear of Kirchhoff'wbrs law
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
At 12:07 PM 03/25/08, you wrote: At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote: Anyhow, without a fuse, the reverse protection diode or transorb in the radio tries to short and shunt the reverse current from the radio. So you are saying it is in parallel (and reverse direction), not series (in forward direction)? Parallel wired reverse protection diodes are standard design procedure. Have been for years. They gut away from series diodes in the 1980s... and for a good reason. I saw this years ago on a Midland 220 mobile that was rated at 10w. At 13.8-14v (the average automobile the output was 12-13w or so. with a voltage drop of only 7 tenths of a volt (the average drop across a series diode) the output power was 8 to 9 w. Modern radios with power bricks don't show that as much, but you get the idea. But a series diode still isn't going to save you in the dual battery situation with the starter motor sucking 300 (or so) amps and putting inductive spikes back on the line. Mike
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote: Anyhow, without a fuse, the reverse protection diode or transorb in the radio tries to short and shunt the reverse current from the radio. So you are saying it is in parallel (and reverse direction), not series (in forward direction)? -- Dave Gomberg, San Francisco NE5EE gomberg1 at wcf dot com All addresses, phones, etc. at http://www.wcf.com/ham/info.html -
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
At 09:56 3/25/2008, Steve S. Bosshard (NU5D) wrote: Anyhow, without a fuse, the reverse protection diode or transorb in the radio tries to short and shunt the reverse current from the radio. So you are saying it is in parallel (and reverse direction), not series (in forward direction)? -- Dave Gomberg, San Francisco NE5EE gomberg1 at wcf dot com All addresses, phones, etc. at http://www.wcf.com/ham/info.html -
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
Depending on the load connecting across one battery, the one connected to ground or the lower of the 2 12 batteries, will work. I would not do is load is heavy because I am sure the charging system is for both batteries and draining one much more than the other could upset things. Kirchhoff's current law says the sum of the currents will be zero. Kirchhoff's voltage law says sum of voltages will be zero. Not sure why revelant here, but I am sure Kirchhoff had something else to do with voltage and current sources. Would like to know. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] Date: 2008/03/24 Mon PM 04:36:54 CDT To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc This is a very common issue in aircraft. The most obvious question is does your jeep use 2 each 12 volt batteries? If so, simply connect your radio across one of 'em. This is done all the time but is a very, very bad idea. Ever hear of Kirchhoff's law? Check it out. It's a very quick way to ruin two batteries. Get a real converter. The switching kind are much more efficient than the linear voltage dropping kind. Al, K9SI Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
RE: [Repeater-Builder] Re: 24 vdc to 12 vdc
The practical effect is that the charge on the two batteries will be imbalanced, and should the charger ever get the more charge battery fully charged, the under charged battery will fool the charger into thinking the pair is not fully charged, resulting the in the fully charged battery being overcharged, and if not quickly damaged, then at least dramatically reduced in lifetime. Some sort of converter is required to keep the load balanced across both batteries, and therefore the charge on the batteries balanced.. whether it be Xantrex or Astron. either will do the job and protect your batteries. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Tuesday, March 25, 2008 6:04 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: 24 vdc to 12 vdc Depending on the load connecting across one battery, the one connected to ground or the lower of the 2 12 batteries, will work. I would not do is load is heavy because I am sure the charging system is for both batteries and draining one much more than the other could upset things. Kirchhoff's current law says the sum of the currents will be zero. Kirchhoff's voltage law says sum of voltages will be zero. Not sure why revelant here, but I am sure Kirchhoff had something else to do with voltage and current sources. Would like to know. 73, ron, n9ee/r From: Al Wolfe [EMAIL PROTECTED] mailto:k9si%40arrl.net Date: 2008/03/24 Mon PM 04:36:54 CDT To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: [Repeater-Builder] Re: 24 vdc to 12 vdc This is a very common issue in aircraft. The most obvious question is does your jeep use 2 each 12 volt batteries? If so, simply connect your radio across one of 'em. This is done all the time but is a very, very bad idea. Ever hear of Kirchhoff's law? Check it out. It's a very quick way to ruin two batteries. Get a real converter. The switching kind are much more efficient than the linear voltage dropping kind. Al, K9SI Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
I have installed land mobile stuff in Gov Surplus fire equipment, (right next to Fort Hood) and 24 volt Forestry Service and 24 V street sweeping equipment over the years. I will NOT install any equipment across one battery in a 24 V string. Take it somewhere else and let them do it. I will not. Without exception, from a RaVo street sweeper to a 2.25 ton truck, the driver will forget and leave the equipment turned on that is across the one battery resulting in that one battery going dead. Now picture this. 2 batteries in a string. One dead, one hot and healthy. Just for sake of discussion. lets say the radio / siren, stuff is across the bottom battery. Neg to GND, Positive to the Radio / Siren stuff AND the Negative of the second battery. Positive of the second battery to the starter solenoid, etc. As long as both batteries are charged this works GREAT. When the bottom battery is dead, and the top battery is OK, and the driver hits the Cole Hersey Switch and tries to crank the engine it is just as though the first battery was no longer there. Remember that the Positive of the bottom battery (now dead) is connected to the Negative if the second battery, thru the starter motor and back to ground. This effectively does 2 things. 1 - reverse polarity is applied to the dead battery and whatever equipment is hooked to it. 2 - The cranking current will be in excess of 400 amps. The fuse in the Neg side of the radio most likely won't make any difference because the case of the radio is tied to the chassis of the vehicle - ground. The fuse in the positive side (if present) may save the radio, but most often, the audio PA and RF PA are history as well as any protection diodes - 10 amp protection diode against 400 amp starter current - no contest. So, spring for the Astron or NewMar or whatever DC-DC converter - I like the fully isolated if possible or else I would encourage anyone to stay away from the one battery connection. Forklifts are even worse. Remember it is just a matter of time before stuff gets smoked... Steve NU5D School of Hard Knocks... Ron Wright wrote: Depending on the load connecting across one battery, the one connected to ground or the lower of the 2 12 batteries, will work. I would not do is load is heavy because I am sure the charging system is for both batteries and draining one much more than the other could upset things.
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
At 05:22 3/25/2008, Steve S. Bosshard (NU5D) wrote: any protection diodes - 10 amp protection diode against 400 amp starter current - no contest. Steve, this confuses the dickens out of me. I now understand the reverse polarity part, but won't the protection diode be reverse direction, and therefore the only relevant stat is the reverse voltage, 12v, and therefore presumably within ratings? I don't see what the current has to do with it because the diode will be non-conducting. The current rating is only for the conducting direction, right? -- Dave Gomberg, San Francisco NE5EE gomberg1 at wcf dot com All addresses, phones, etc. at http://www.wcf.com/ham/info.html -
Re: [Repeater-Builder] Re: 24 vdc to 12 vdc
This assumes that the installer did not fuse the + lead to the radio. Normally a 25 to 35 watt radio has a 15 amp fuse but you might be surprised how many times the power cable has been cut and no fuse. Anyhow, without a fuse, the reverse protection diode or transorb in the radio tries to short and shunt the reverse current from the radio. Most of these can handle about 20 amps for a few seconds before the smoke gets out. Then the reverse protection diode is essentially gone and next in line us usually the audio power amp, and RF PA. While the radio tries to act like a short (for a few brief moments during cranking with the first battery dead the starter will draw hundreds of amps (or try to) thru the radio and protection diode. This doesn't continue very long at all. If the radio is properly fused, then the diode may short and blow the fuse, but without a fuse, the radio gets blown. Steve Dave Gomberg wrote: At 05:22 3/25/2008, Steve S. Bosshard (NU5D) wrote: any protection diodes - 10 amp protection diode against 400 amp starter current - no contest. Steve, this confuses the dickens out of me. I now understand the reverse polarity part, but won't the protection diode be reverse direction, and therefore the only relevant stat is the reverse voltage, 12v, and therefore presumably within ratings? I don't see what the current has to do with it because the diode will be non-conducting. The current rating is only for the conducting direction, right? (with one battery dead, the other battery will cause reverse current thru the first battery during cranking and at that time the protection diode will be briefly conducting). -- /Subscribe to dstar_digital/ Powered by groups.yahoo.com http://groups.yahoo.com/group/dstar_digital/
