Reverse Polarity Protection in Desulfator - 555 based and all pulse output stages Forum

RSS
Email

0 Points

Reverse Polarity Protection

Author	Comment
desulfator2	Reverse Polarity Protection	Lead	[-]
Posts: 1052 Apr 27 04 10:36 PM Reply Quote More My Recent Posts	Tags : None I was looking at a relay and noticed that the contacts were mounted on wide flat conductor which appeared sufficient for a high frequency skin effect pathway (wide strips of conductor). The same was true of the woven conductors feeding the strips from the solder connections at the bottom of the relay. I had thought that with any pulser/charger, reverse polarity protection could be afforded by a 12V relay with a diode in the coil circuit. It would only connect the battery to the pulsing/dedendriting circuits if connected with the proper polarity. This concept would not work well with 555 based pulsers, due to contact arcing and burning at the time of disconnect. An absorbing capacitor shunting the contacts will probably not be enough to prevent contact arcing and burning. The same would be true with micro controlled pulsers without charging capability as there would be no way to clean the contact surfaces. However, with a pulser/charger that is not connected to a battery, the relay could have a cleaning routine. A push button switch could force the solid state relay controlled charging circuit on to enable the micro. The micro once enabled could detect the button push early in the program. This detection could jump to a relay cleaning routine that simply chatters the relay for a few minutes to clean and flatten the contact surfaces. I suppose a refinement of this routine would check the relay contact resistance and continue the chatter until the contacts cleaned to an acceptable range of resistance. Ultimately a warning light would be needed to warn the operator that the relay needed changing if the resistance would not drop after X minutes of chattering or cycling. Currently I'm working on a 28X pulser/charger. I'll try to incorporate this feature in it and post the results. I'd do it tonight but I can't find my 12V relays that I pack ratted away somewhere amongst my many treasures.
	Remove this ad
desulfator2	Re: Reverse Polarity Protection	#1	[-]
Posts: 1052 May 2 04 6:52 AM Reply Quote More My Recent Posts	Initial testing with relays here suggests two things, 1. Radio Shack relays are really tough 2. Vibrating a burned contact set reduces resistance I had thought that a DPDT relay using the NC contact set for normal conduction/connection between the positives of the battery to pulsing output stage could serve as reverse polarity protection. With the coil of the relay wired with a diode in series it could disengage the NC set of contacts in the event of reverse connection. I suppose you could use the NO set of contacts to engage the pulser and pulsing output stage positives but that introduces an additional 70ma load while things are perculating away. Not really a bad load if you are using a trickle charger for offline recovery but might be a bit much if connected to your favorite chariots battery overnight. For the brief period of conduction through the contact set, it was felt that in time they may arc and burn enough to increase the contact set resistance and then impede pulsing. To counter this, I had thought that by chattering the relay it would abrade the damaged area of the contact set cleaning the connection for a low impedance path. To test this theory I took a small 12 volt, 5 amp relay from my stock of treasures and modified it. As received it came with narrow gauge conductors leading to the contact set. The small conductors were removed and desolder wick installed. Using my trusty Fischer Price LCR meter the paralleled contact set measured 0.06 ohms. I used a small 12V transformer to chatter the contact set. While the contacts were chattering away I used the contacts to directly short out a fully charged 12 volt, 7AH battery. Sure enough the contacts emitted a bright blue arc. Within about 5 seconds the interior of the relay filled with smoke and the desolder wick started to fuse with the plastic exterior case. After allowing a cool down of a few minutes the contact resistance measured 0.07 ohms The relay coil was then once again connected to the small transformer to chatter the contact set for 5 minutes. The relay was disconnected and allowed cool down time. The contact set resistance returned to 0.06 ohms. I was left with the impression that, 1. Radio Shack relays are really tough 2. Vibrating a burned contact set reduces resistance 3. As the contacts proved to be very durable during the severe loading test, perhaps a modified relay could be used with 555 based pulsers for reverse polarity protection. I suppose the next phase of testing would be to see how well a pulsing output stage tolerates a brief reverse connect. I'l post again after the smoke clears and the dust settles.
desulfator2	Re: Reverse Polarity Protection	#2	[-]
Posts: 1052 May 4 04 7:53 AM Reply Quote More My Recent Posts	Well I gave it a shot by using the relay's NC contact set for correct polarity connection of the battery and pulser positive leads. Not Good! The relay did not retract in time and the circuit board blew a circuit board tracing. However, with the trace repaired, all circuit components appeared to be working normally. Although this confirmation did not involve scoping outputs. Further experimentation is called for with beefed up circuit pathways to avoid the tracing burnout. I had also thought that a diode in series with R3 could be used for additional protection for the 555 and C1. It may be better to use both NO contacts to provide a pathway for proper connection, but this imposes an additional 70ma load on the battery. Not a problem if you are doing offline conditioning with a trickle charger or the pulser is connected to a deep discharge bank. But this may impose too much of a load on a marginal starter battery being conditioned while online.
Ed	Re: Reverse Polarity Protection	#3	[-]
Posts: 361 May 4 04 11:21 PM Reply Quote More My Recent Posts	Reverse polarity protection is simple - permanently attach a led and series resistor to the pulser + on the board. Connect the + pulser lead to the battery. The other connection to the led/resistor is free. It gets connected to the battery BEFORE the remaining pulser lead. If the LED lights, connect the remaining pulser lead. If it doesn't, then the plus lead from the pulser is connected to the wrong battery terminal. If you want to use a relay: If a relay can be placed in the pulse path with no adverse effect on pulsing, then protecting it from arcing is simple. Don't use it to turn the circuit on or off. Use it to enable one leg of the pulser (+ or minus, doesn't matter). Here's how: * The relay has a diode in series with the coil such that it energizes only when properly connected to the battery. * The battery connects to points AA and BB * CC and DD are the relay contacts (normally open) * The + lead of the pulser connects to CC * The + lead of the relay connects to AA Pulser lead---CC DD--------AA-RelayCoil-BB Pulser lead------------------- connects to BB after the battery is connected to AA and BB Note that one pulser lead is permanently connected to the open relay contact - the other pulser lead is free. Connect the two relay coil wires to the battery first, then connect the remaining pulser lead to the battery. When you disconnect, remove the free lead from the pulser first. If you hook it up backward, nothing happens because the relay doesn't energize.
desulfator2	Nice Radio Shack Relay for Reverse Polarity Protection	#4	[-]
Posts: 1052 May 7 04 6:55 AM Reply Quote More My Recent Posts	Radio Shack has a 4PDT relay (275-214) that provides two more contact sets to lower any impedance across the contacts. Naturally the relay must be reworked. The internal wire conductors must be replaced with something like desolder wick. This is necessary in order to avoid a large impedance chokepoint in the conductive path between battery and pulser.
franz mpf	Re: more simply	#5	[-]
Posts: 19 May 8 04 8:28 PM Reply Quote More My Recent Posts	maybe this is more simply: rearmable desulfator-----------magnetic/term 5A------- + battery \| \| \|--------\| \|---------------- \| 10 uf K 20A diode A \| \| gnd
franz mpf	Re: more simply	#6	[-]
Posts: 19 May 8 04 8:51 PM Reply Quote More My Recent Posts	more simply (write to paper, sorry)
desulfator2	Re: more simply	#7	[-]
Posts: 1052 May 14 04 8:55 AM Reply Quote More My Recent Posts	Does not appear to be a viable circuit. You would kill the pulse attempting to go through the relay coil.
Anthony Doyle	Re: more simply	#8	[-]
Posts: 177 May 15 04 7:27 AM Reply Quote More My Recent Posts	I might be totally missing the point or stating the obvious; but couldn't you just use a relay and a diode? Connect the relay coil in series with a diode between +ve and -ve. Then have the relay contacts in series with the desulfator. If connected correctly, circuit switches on. If not, the diode stops coil current, relay contacts stay open and therefore nothing happens. Simple.
franz mpf	Re: more simply	#9	[-]
Posts: 19 May 17 04 9:32 PM Reply Quote More My Recent Posts	sorry for my english. this is my block call "Magneto thermic" or better "Magnetothermic blocking with manual restart" too much simplified may be. normally contact are closed. when current is + then nominal value, contact change to open and is necessary re-armed. C 10 uF bypass desulfator-spike from the coil of Magnetothermic. Diode is in conduction if battery polarity reverse (like a c.c.) and Magnetothermic disarmed. 1mH open possible interference diode-spike
desulfator2	Re: more simply	#10	[-]
Posts: 1052 May 18 04 1:19 AM Reply Quote More My Recent Posts	Hi Anthony, Preliminary testing here is encouraging. I've switched to using the NO contact set of a DPDT relay (both poles used to connect POS battery to POS pulser. Scan of DPDT pins which also uses desolder braid externally for a low loss connection home.comcast.net/~ddenhar...DTpins.jpg A 100 ohm resistor seems to reduce the milliamp requirement for holding. But I've yet to run voltage tests to insure it will close at 10.5V with a 100 ohm R in the coil circuit. Last test to pull is measuring pulse amps across a .006 ohm shunt using the contact set as opposed to having them externally shorted. I am shifting my lab to the living room so that I can watch DVD's while running extended tests that require close supervision. I've yet to move some L-16's into the living room, but I'll get aroundtoit one of these days. Next I'll measure any difference between the DPDT and a 4PDT relay. Here is a sort of before and after scan of the 4PDT relay modified to replace the skimpy internal contact wires with desolder wick. home.comcast.net/~ddenhar...4PDTBA.jpg After comparison tests are done between DPDT and 4PDT relays (contact losses), I intend to program a PICAXE to excercise the relays for a few thousand Makes and Breaks to get an idea of how bad the contact sets fare.
	Remove this ad
als	Re: more simply	#11	[-]
Posts: 375 May 18 04 3:24 AM Reply Quote More My Recent Posts	Why not toss the relays completely, and add a couple more diodes? Just isolate the feed from the output, and insert. A _ton_ more reliable. And cheaper. Since I started building all my pulsers with separate inputs and outputs, this is very easily done here. I had run smaller wires parallel to the big cables anyway, in order to get a more accurate reading direct from the battery terminals. One could use the smaller wire to feed the large inductor and timer circuits. I don't, since all my setups include a trickle charge to make up for pulser draw and self-discharge. (As an aside, it will be interesting to watch for any accelerated improvement; my latest batch of tricklers are pulse-mode). <als>
desulfator2	Re: Re: more simply	#12	[-]
Posts: 1052 May 18 04 8:41 AM Reply Quote More My Recent Posts	Hi Als, I couldn't follow what you were saying. How does one seperate inputs and outputs with diodes. Guess I need to see a picture.
als	Re: Re: more simply	#13	[-]
Posts: 375 May 18 04 3:03 PM Reply Quote More My Recent Posts	Sorry. It just seems obvious to me. Look at: people.txucom.net/andysm/...html#3fet1 (You can leave out the extra 2 FET's). Add another forward-based diode to the terminal labelled "BAT +" and connect the power supply input terminal to the smaller positive lead from the battery. Use Schottkey diodes if you wish to minimize the voltage drop. <als>
als	Re: Re: more simply	#14	[-]
Posts: 375 May 18 04 3:18 PM Reply Quote More My Recent Posts	Stupid me. Shoulda actually LOOKED at what I was pointing you to, before posting the message. Add: And move L2 to connect the cathode of D8 to the L1/C3/C2/R10 junction. The added diode(s) should not be necessary in this case. <als>
desulfator2	Re: Re: Re: more simply	#15	[-]
Posts: 1052 May 18 04 6:33 PM Reply Quote More My Recent Posts	I dunno Als, I looked at the circuit and was somewhat puzzled. Won't R7/R9 feed a POS to the NFET gate (smokin inductors)?? On a reverse connect, won't D1~D3 and D6 pop? Maybe I was looking at the wrong schematic. At any rate my immediate goal is to come up with a low tech reverse polarity protection for the AC standard and NFET output stages.
als	Re: Re: more simply	#16	[-]
Posts: 375 May 18 04 11:06 PM Reply Quote More My Recent Posts	Yep, yer right. Reversed connections would cause a direct path thru the diodes. Dunno what I was thinking about; probably another supply connected to the battery at the same time not affecting the pulser, or something of that nature. Would still work if you added a healthy fuse, tho. I confess that I have not given the reverse polarity problem much thought - I just don't hook 'em up backwards. If it truly is a problem, get some of the colored soaked terminal pads, and use color-coded cables. Red Sharpie's or Marks-a-lot on the terminals and/or cable ends, or some such. As far as the pullup; all my separate timing modules have active high outputs (and therefore are grounded when OFF). Guess I should have made that more clear. <als>
Anthony Doyle	Or...	#17	[-]
Posts: 177 May 20 04 1:31 AM Reply Quote More My Recent Posts	Simply: Put a high current diode in series with a fast blow fuse between the +ve and -ve leads. When reverse connected, the fuse should blow first.
DonaldPlisc	Re: Or...	#18	[-]
Posts: 48 May 20 04 7:02 PM Reply Quote More My Recent Posts	Anthony, I like that idea; It's simple...Would the fuse be able to blow fast enough to keep damage from being done to rest of the circuit? Would that somehow interfer with the pulse when normal polarity is applied? Would the pulse want to feed thru it in normal opperation?
Ed	Re: Or...	#19	[-]
Posts: 361 May 20 04 11:48 PM Reply Quote More My Recent Posts	The fuse and diode in series would add unacceptable increased impedance, if you are trying to maximize pulser effectiveness. Here what you can do, at no cost to pulser performance. Add a diode, an LED and a resistor in series, and a wire to the circuit. You are going to end up with a 3 wire (instead of 2 wire) pulser. The series diode and led get soldered to the negative pulser lead. The other end of the series diode and led goes to the third wire. When you connect your pulser to the battery, connect the negative lead first. Touch the third wire to the remaining battery terminal. If the LED lights, then and only then connect the remaining pulser lead to the battery post. The added circuit: Neg---diode--led--resistor---third wire (the above edited because the symbols I drew using a less than symbol and forward and reverse slashes messed things up) The diode protects the LED if you wire it backwards. Use a 1K resistor. The wires for this circuit can be any gauge that is practical. Even if it is dark and your eyes are tired, this will positively prevent a misconnection if you follow the rule: no light, no good. Ed
Anthony Doyle	Re: Or...	#20	[-]
Posts: 177 May 21 04 5:32 AM Reply Quote More My Recent Posts	Hi Don, Although it would work, the fuse in one of the leads would attenuate the pulse too much. I think either the relay, or Ed's idea is the way to go. I have a fuse between L2 and the adjacent lead. This protects the pulser for most problems other than reverse connection, without getting in the way of the pulse current.
	Remove this ad

<< Previous Topic Next Topic >>

Yuku free message boards

Reverse Polarity Protection

Reverse Polarity Protection