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Car Forum / Driving, Maintenance, Tuning / RVs / January 2008isolation diodes, solenoid, FETs
I've been putting off checking out my charging system. I installed a CD deck and a rear view camera/monitor and happen to measure the dashboard voltage as over 15 VDC. Reading Bob Livingston's Repair & Maintence Manual, he describes a typical isolation system with two diodes heat sink mounted. Under alternators he describes various makes and models. I'll need remove the passenger seat this weekend to get a good look in the engine compartment and the alternator. I expect I have an isolation solenoid as I found online mention of an old Clark motorhome with a similar key-on solenoid closing sound. Mine is a small 1983 Lindy on a Chevy frame. When I first looked at the cabin battery it was boiled dry. The area had been rebuilt and I had a tough time fitting a pair of 6 volt golf cart batteries. These aren't yet wired in as I want to put a 1 ohm power resistor in series and measure the charging current as I suspect the 12 volt battery I removed had been overcharged. I figure the 15 volt plus I measure at the dashboard would only be right if there were an isolation diode from the alternator to each of the batteries. Until I read of the isolation solenoid I supposed that only the cabin battery was isolated by a diode given that the alternator could drive the cabin lights with no cabin battery but those same lights would die if the alternator stopped putting out (engine stopped) and additionally this would explain the dash at 15+volts. I could probably leave the solenoid and add the diodes as the cleanest fix. There's still the question of what kind of alternator is actually in there and if there is a voltage sensing wire that needs to be placed correctly. Also, there's the question of how much charge current I will need anticipate and where I'll get the diodes. I probably have a good heat sink among my junk and I've mounted a good many TO-3 power transistors to know the drilled aluminum heat sink needs to be deburred with steel wool so the mica insulator isn't punctured. So, has anyone successfully used any Radio Shack power diodes for this task? There's the question of the power FETs with a Linear LTC4412 as described in this article. http://www.discovercircuits.com/H-Corner/bat-iso.htm If this circuit is okay I would suppose it's only good if the alternator puts out 14.5 volts not 15.3 or 15.4 volts. Bill > I've been putting off checking out my charging system. I installed a > CD deck and a rear view camera/monitor and happen to measure the [quoted text clipped - 35 lines] > If this circuit is okay I would suppose it's only good if the > alternator puts out 14.5 volts not 15.3 or 15.4 volts. There's no need to re-invent the wheel. You can pick up a diode style isolator at just about any auto parts or RV supply store. http://www.ase-supply.com/category_s/20.htm?gclid=CJ2Yo_CqpJACFRscawod4TEL7A Your solenoid isolator should be just fine. The "house" battery was probably "boiled dry" from lack of maintenance. Consider: your chassis battery is being charged off that same alternator. Many people consider solenoid isolators to be superior to diode isolators. If you search through the archives Neon Jonh has a good rant or two on the subject. You might find it on his website too. TB The referenced circuit is not that good for the following reasons: 1. Schematic drawn incorrectly. 2. The FETs have a channel resistance of .02 ohm. At 10 amps of current they are dropping 0.2 volts. Since when are they so much better than Schottkys? 3. The FETs are rated to +/- 20V Vgs max. Since there are no voltage clamps or load dump protection this circuit is prone to blowing. 4. The circuit would not pass any automotive type acceptance testing. 5. Too many parts, go with diodes. 6. There is no load balancing for the paralleled FETs. Failure or compromise in one may lead to failure of all of them. Go to the simplest solution - diodes. > The referenced circuit is not that good for the following reasons: > [quoted text clipped - 14 lines] > > Go to the simplest solution - diodes. Thanks. Not thinking clearly I supposed I'd use a tremendous Dale power resistor I picked up at a ham fair but I'll probably go with a . 15 Dale so I don't voltage limit. Since the batteries are new I can check the charge current with and without their isolation diode in place. Looks like there's a delay due to the holidays as to when a mail order vendor can get an isolator in the mail to me. Radio Shack doesn't stock heavy diodes though they do stock PNP TO-3 power transistors. I wonder if I could get away with tying the base to the collector or if the base would open. I didn't get the TO-3 part number, the question is as a rule. Bill > Not thinking clearly I supposed I'd use a tremendous Dale > power resistor I picked up at a ham fair but I'll probably go with a . > 15 Dale so I don't voltage limit. Light bulbs make great cheap power resistors. The energy is dissipated in the form of light and heat so it doesn't get as hot as resistors. 100 watts is no problem, don't need an oil bath or any other form of cooling. Get your incadesant bulbs soon before the greenies outlaw them. > > Not thinking clearly I supposed I'd use a tremendous Dale > > power resistor I picked up at a ham fair but I'll probably go with a . [quoted text clipped - 4 lines] > is no problem, don't need an oil bath or any other form of cooling. Get your > incadesant bulbs soon before the greenies outlaw them. Okay, using a .1 ohm Dale power resistor I found unexpectedly that the batteries are in the compartment backwards and trying to wire them up makes for a strong flash. The hot is black and ground white. Anyway, the shorepower power supply puts out 12.5 VDC and there is no current flow into the brand new and assumedly fully charged batteries. Using the engine running with closed solenoid however causes 750 mv to be dropped across the .1 ohm resistor. This is telling me the batteries are charging at a rate of 7.5 amps while fully charged. The voltage drop across the power resistor isn't so much less than one would expect from a heavy duty diode although at 7.5 amps that drop will be higher, still... Bill > > "Bill" <wtjohns...@gmail.com> wrote in message > [quoted text clipped - 22 lines] > > Bill Okay, I installed an isolator. As directed I disconnected the BAT wires at the alternator. I ran a cable from the BAT (alternator output) to the A terminal of the isolator (anode of both diodes) and from one of the cathodes I ran a cable back to the wires I disconnected from BAT terminal of the alternator. Next I connected the cabin 12v in to the other cathode. Now the cabin battery gets 14.5 volts BUT the dash still gets 15.4 and measuring the actual alternator output (A to ground) I get over 16 volts. So, somebody tell me what's going on please. Bill >Okay, I installed an isolator. As directed I disconnected the BAT >wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 8 lines] > >Bill Either a bad voltmeter or a bad alternator. >>Okay, I installed an isolator. As directed I disconnected the BAT >>wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 10 lines] > >Either a bad voltmeter or a bad alternator. Did you ever figure out the problem? dean >>Okay, I installed an isolator. As directed I disconnected the BAT >>wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 10 lines] > >Either a bad voltmeter or a bad alternator. Did you ever figure out the problem? dean > >>Okay, I installed an isolator. As directed I disconnected the BAT > >>wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 14 lines] > > dean Sorry guys. Am on road home. Lots of shakedown problems. Had a transmission cooler put in. Broken vacuum fitting. Muffler broke. Will figure out the wiring when I get home. > > >>Okay, I installed an isolator. As directed I disconnected the BAT > > >>wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 20 lines] > > - Show quoted text - Well, that won't be happening. The camper burned today. Total loss. Took my wallet. I got out with my dogs. Well, that won't be happening. The camper burned today. Total loss. Took my wallet. I got out with my dogs.<<<<< HOLY sh.t !!!! Glad to hear you and the dogs got out OK. Any idea of what started the fire ?  SignatureJerryD(upstateNY) On Jan 2, 1:52 am, "JerryD\(upstateNY\)" <jer...@justask.com> wrote: > Well, that won't be happening. The camper burned today. Total loss. > Took my wallet. I got out with my dogs.<<<<< [quoted text clipped - 5 lines] > -- > JerryD(upstateNY) The carb was never set up right. I was only getting 6 mpg. I went to change the fuel filter on my way up to NY and found there was none. Since the camper was probably sitting for months before I bought it there could have been scales on the gas tank that now got free. So for the rest of the trip I hoped to just get by and rebuild the carb when I got home. I put in an inline filter when I found there was none. On my way back, in NC, another camper much like mine cruised right by comfortably. Mine had no power. I decided that next time I stop I'll try and fix it before starting again. I opened the engine compartment (inside) and took off the air filter. I could see that of the four barrels only the front two would open no matter how far I opened the throttle. I tried to manually work the real butterflys and they did move properly if I put a screwdriver in. Working the throttle I kept pumping in fuel so since that didn't look good I disconnected the fuel line (but didn't plug it). I got caught up in the complexity of the linkage and forgot about the fuel line. When I went to start it I got pumped over with gas. I was on my knees in cab when the engine started. I quickly put my right hand over the pumping gas line and turned off the ignition with my left but I was covered in gas and it ignited. My right hand and arm and chest on fire I took off my sweatshirt and got it out. I grabbed my brand new fire extinguisher from Walmart and thinking what a mess the powder or liquid was going to make, tried to use it. I got nothing, just a dribble of water and foam, not a quarter cup full. I got my dogs out and my bicycle off its rack and the rack off. The fire department was called but the propane had already ignited (discharged through the roof) and was done by the time they got there. I have second degree burns of my right hand. Some pretty big blisters. So, I must have been driving on 2 barrels while gas might have been pumping in all 4. Explains the backfires. On the way up a shoddy vacuum line port repair on the intake manifold turned up. The vacuum line had broken off at the port and somebody had stuck it on with just a short piece of hose. I put in a more effective temp fix with RTV and wire ties. Bill Bill wrote:I got caught up in the complexity of the linkage and forgot about the fuel line. When I went to start it I got pumped over with gas.<<< Glad to hear you didn't get burned too bad. I did the same about thing some years ago. SignatureJerryD(upstateNY) On Jan 2, 11:22 am, "JerryD\(upstateNY\)" <jer...@justask.com> wrote: > Bill wrote:I got caught up in the complexity of the linkage and forgot about > [quoted text clipped - 5 lines] > -- > JerryD(upstateNY) Darn, only having liability on the vehicle, it's a total loss but I had hoped some new equipment was covered because it was purchased on a credit card. The credit card company, issued from the largest bank in the US, says no. Is this correct anyone know? > On Jan 2, 11:22 am, "JerryD\(upstateNY\)" <jer...@justask.com> wrote: >> Bill wrote:I got caught up in the complexity of the linkage and forgot about [quoted text clipped - 11 lines] > credit card. The credit card company, issued from the largest bank in > the US, says no. Is this correct anyone know? Bill, I was glad to read you and the dogs made it out OK. How are the burns? Now, about credit card coverage. Keep asking and ask as many different ways as you can. The policy is bank and card specific, but you might just find someone that will admit that this was are covered. Did you have homeowners? Some of the things you bought may not have been RV specific and you were just transporting them.. Next? Did the loss (fire) actually occur this year or last? (If it was actually after midnight -01 January 2008, you have plenty of time to get the documentation in place.) Do you file income tax long form? ....You will this year. Between bad debt, uninsured casualty loss and capital losses, you should be able to Zero this year and maybe carry some over to next. This is another one where you have to keep asking everybody you know if they know a truly vicious tax person. If he is any good, he will not be taking on new clients. Try to talk to him anyway. Tell him your problem and promise that you will have your paper together, be prompt at meeting on his schedule and only plan to bother him this year (if he so desires) and with luck he'll help you. BTDT (long story) Matt Colie > I was glad to read you and the dogs made it out OK. > How are the burns? Right hand. It will heal. > Now, about credit card coverage. > Keep asking and ask as many different ways as you can. The policy is > bank and card specific, but you might just find someone that will admit > that this was are covered. > > Did you have homeowners? No. > Some of the things you bought may not have been RV specific and you were > just transporting them.. > > Next? > Did the loss (fire) actually occur this year or last? Morning of the 1st. > (If it was actually after midnight -01 January 2008, you have plenty of > time to get the documentation in place.) [quoted text clipped - 10 lines] > meeting on his schedule and only plan to bother him this year (if he so > desires) and with luck he'll help you. Thanks Matt. I try to do my own taxes though this might be a trial. Bill > Okay, I installed an isolator. As directed I disconnected the BAT > wires at the alternator. I ran a cable from the BAT (alternator [quoted text clipped - 8 lines] > > Bill Bill, Your connection is correct. The reported values are a little strange, but are consist with some bad of missed connections. The IP seeing 15.4 is high, but not very. It is high enough to shorten the life of the lamps. The fact that the cabin (coach) battery is showing 14.5 is good, but is it being regulated to that or it the battery clamping to that by charging - we don't know. What is the start (engine) battery showing? I have frequently seen alternator terminal voltages as high as 18+ during heavy charging. I can't find my books right now, but I remember that the single foot GM alternator senses on little terminal (I think marked +) and not the battery terminal. Before you do much else, confirm that this is how the alternator you have is supposed to function. Then confirm that the sense lead does go someplace real near one of the battery terminals. Matt |
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