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Bigbob
| | Posted on Saturday, October 19, 2002 - 6:56 am: | 
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Can you have a battery hooked to a power supply or would it discharge through the circuits,course I could switch it with knife switch,or are they not compatible? |
fred
| | Posted on Saturday, October 19, 2002 - 10:08 am: |
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Get you a 1.0 farad cap instead. |
2600
| | Posted on Saturday, October 19, 2002 - 4:31 pm: |
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A lot of power supplies would be just fine UNTIL you turn off the supply. The battery will discharge back UPSTREAM into the thing and hurt it. Some power supplies won't like the big cap, and some of them will. That's a lot harder to predict.
A former boss of mine used a big solenoid relay to turn on a battery to 'assist' the power supply on big loads. So long as the power supply didn't shut down, it worked fine. When the battery was no longer needed, you switched the relay back off, BEFORE turning off the supply.
73 |
Deadly Eyes
| | Posted on Saturday, October 19, 2002 - 8:26 pm: |
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Re 2600
In reference to the realy comment, I have read posts where people have while in the process of wiring directly to the battery inserted a heavy duty relay in the power circut. When he ignition was off the relay was inactivated killing power to the radio and thus saving the battery. When the key/ignition was on the relay kicked in and the radio worked fine.
I just hesitate to suggest it because the more junk you have in a circut or system there is more stuff to become damaged. And ol Murphys Laws have yet to be repealed. ;-)
Later
DE |
bruce
| | Posted on Saturday, October 19, 2002 - 9:01 pm: |
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I have to ask WHY? the cost of a battery would it not be better money spent to just but a heaver supply? I run my ham station off ONE 20 amp supply and it stays cool if i needed more for less that 100 bucks i can buy a 30 amp supply and under 200 a 50 amp one. i did the battery trick back in the 70's and never found it to be of great value.... the first time i got a good supply i never used a battery since. |
Bigbob
| | Posted on Saturday, October 19, 2002 - 10:50 pm: |
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All I would need is a 30 amp relay just to cover the holes and tie it to the amp relay so both work together.Fred I am powering a boomer 400 driven by a dx2517,my supply has 5 mj2955 pass transistors(I just got tired of drilling holes)a 40 amp transformer(continuous)10-4,700uf caps(filter)317t with by-pass for 80db ripple rejection,and a stinger 1-farad cap with built in volt meter,oh yeah 8-guage cable,and I still get 1 to 1.5 volts drop on ssb and 2 volts on am with an swr of 1.17 hence the battery.Hows that Fred? |
Bigbob
| | Posted on Saturday, October 19, 2002 - 10:53 pm: |
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By the way my 1-farad cap has a built in in-rush limiter,very cool,$165. |
monk
| | Posted on Sunday, October 20, 2002 - 5:29 pm: |
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The easy way to run a power supply and battery is to put a diode of the correct amp rating in the positive line and readjust the power supply voltage to make up for the diode voltage drop (.7volt). No relays needed and the battery won't whack the PS when it is turned off.
Monk |
Bigbob
| | Posted on Sunday, October 20, 2002 - 10:41 pm: |
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need a minumum 30 amp diode,what about a coil of 2 guage cable on a 3"x12" ferrite rod 100turns in series with 1 farad cap,I know I know bruce why bother,well like I said about the other guy if I got the money then it's mine to waste. |
ss8541
| | Posted on Monday, October 21, 2002 - 12:15 am: |
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you are right monk. i make battery back ups for repeaters this way. i use a 35amp bridge rectifier mounted to a hink sink which is then mounted to the battery. if you are going to use something that is going to pull more than 30amps continuous you will want to use 2 or more bridges.
wire power supply to bridge, then bride to battery, and battery to equipment to be powered. this will keep the battery charged, and keep battery current from going back up into the power supply. it will also keep the power supply from overcharging the battery. if power supply is putting out 14v, then it will stop charging the battery once the battery voltage has reached about 13.5v(bridge stops passing current around .5v difference). |
2600
| | Posted on Monday, October 21, 2002 - 1:39 am: |
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Hey, Monk's got the right idea, but I learned the hard way that you have to rate the diode differently. The rated AC current for a rectifier diode takes into account a 50% duty cycle. The diode is only turned on (and producing heat) HALF the time. The other half of the time it is turned off and NOT producing heat. A diode carrying DC current is producing TWICE as much heat per Amp as an AC rectifier does. A 10-Amp RECTIFIER is really a 5-Amp isolation diode. Monk did say "correct amp rating", but my experience is that the DC Amp rating is HALF the stated AC current they quote for AC rectifier service.
73 |
Deadly Eyes
| | Posted on Monday, October 21, 2002 - 8:22 am: |
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Re Bruce's question...Why?
This is a valid question. Consider, you can go to just about anywere and get a very nice high amp switching power supply for the cost of the battery system you are making reference to.
And if the juce goes out all you have to do is run a wire to the battery in the car for power.
I would be curious to know why ol Big needs an automatic emergency power supply? Just curious th that is all. Just curious. |
Bigbob
| | Posted on Monday, October 21, 2002 - 5:29 pm: |
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For my purposes bruce is correct,so my next question is can you hook 2 40 amp transformers in parallel on input and output for 80 amps ,cause I plan on changing pass transistors to make it a 150 amp supply,peak,that is. |
409
| | Posted on Tuesday, October 22, 2002 - 3:53 am: |
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Only if the transformers are the same and phased properly...... |
ss8541
| | Posted on Tuesday, October 22, 2002 - 9:42 pm: |
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2600, if you split the dc across both sides of the bridge, and it is properly heat sinked, you'll find that it can handle close to the rated ac amperage. that is why i listed 30amp continuous for the 35amp bridge. now the term 'continuous' i'll admit is used loosely. no i have never let 30amps run through a 35amp bridge for several hours, but did have 2 hf rigs running off a set up like this for field day a few years ago for 24hrs(both going almost continuously during daytime hrs). bridge never failed, but did get hot. |
Deadly Eyes
| | Posted on Tuesday, October 22, 2002 - 10:11 pm: |
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Re 409 a technical question in theory....
I completely agree with your post. I have a question concerning a possible way to link two trasnformers that are identical. This is just pure theory of course. What if one were to place the two transformers extremely close so that the connection between the two transformers was as short as possible, the cores were so close so as to provide some core magnetic linkage, and the secondarys were also connected in such a way as to form a center tap. Just thinking out loud would this close linkage be sufficient to cancel out the difference in phase between the two transformers?
Or would just having the primary inputs be connected to a parallel feed circut so that both transformers would see the same phase at the point of input. The secondary side could then be either tied together to get a desired turn ratio. |
ss8541
| | Posted on Tuesday, October 22, 2002 - 10:34 pm: |
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oh yeah deadly eyes i almost forgot your question about why big needs an emergency backup. it isn't that he needs and emergency backup. it is protecting what he has now. with what monk and i suggested, he can cut the power supply off with no worries. if he doesn't go this route, he discharge his battery and could possibly damage his power supply. i just was just simply stating that i have made rptr backups this way. |
2600
| | Posted on Wednesday, October 23, 2002 - 1:28 am: |
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Hi Richard,
A bridge sure ought to take care of the rating problem. Odds are that the individual diodes inside will match pretty well and share the load more or less equally. The proof (poof) is in the pudding. If they hold up, they're big enough.
And Deadly Eyes, the core in a power transformer is supposed to put the magnetic field where the work is done, across the windings inside, not outside. If enough of it 'leaks' into the part next door, it's not a very efficient design in the first place.
Wiring two or more transformers in parallel really does require that they be identical. Linears made by D&A and Firebird did this. D&A had a simple formula. Buy just ONE kind of power transformer. Makes the volume high, cost low. Stocking ONE part number is always cheaper than two or more. Use one transformer for four tubes, two in parallel for eight tubes, up to four of them in the 16-tube(!) model. Sure worked for them.
73 |
Bigbob
| | Posted on Wednesday, October 23, 2002 - 8:43 pm: |
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Thanks for all the input,guys,really.Bigbob |
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