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Forum Index : Electronics : Question regarding capacitors?
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| larny Guru  Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Thanks Yahoo2, A scan of a hand drawn one would suffice. Robert, I'm currently working through your info. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Yahoo2, I assume you're referring to this from warpspeed. You could probably buy a commercial battery charger that used a switching power supply to convert 240 volts ac to properly charge your battery. The way these work, they rectify the ac mains voltage to create a high dc voltage, usually at around 340 volts (for 240v input). That dc voltage is then chopped at high frequency and fairly efficiently transformed down to the required lower voltage to charge the battery. The clever thing about that, would be that you could feed your 290 volts dc, or 350 volts dc, (or whatever you end up having) straight into the 240 volt ac input, and it would work perfectly. The actual input voltage of these switching supplies is non critical, because they are built to accommodate wide variations in mains supply voltage. An unmodified off the shelf unit should do the job admirably. If you want to run both hydo systems in direct parallel, you still can, and have the rectifier at the house. Or have two rectifiers and combine the outputs to feed high voltage dc to the house. Try it both ways, and see how it goes !!! There are advantages and disadvantages either way. Just did an ultra quick Google, a fully automatic 12v 20A battery charger, with fast charging, and float modes $70.00 on flea-bay. There are many comparable products flooding out of Asia that are of similar or identical design. http://www.ebay.com.au/itm/NEW-12V-Battery-Charger-20-Amp-Ca r-Boat-Caravan-/270784868768?pt=AU_Car_Parts_Accessories You can plug high voltage dc straight into the input of something like this, and it will not know the difference. The 12 volt side is completely isolated from the 300 volt side, so it will be as safe as if it was connected to the 240v mains. Robert, This sounds like a good idea, but you will need a switching mode charger, not one that has a transformer. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, The Pow'r Converter.pdf has numerous "schematics". Which one is applicable to your arrangement? And the same question applies to the Handi-Power paper. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, In one place you wrote:- "The other side of the cap plates are connected to the frame of my machine as the outlets in my box are grounded to the case of the alternator through the frame of the generator. (What is the generator? So the diode is to allow the use of the frame instead of adding another wire from alt ground directly to the other set of terminals on the cap and the outlets in the box. (I don't understand this point) My thinking is that the cap would somehow work while charging the battery and work with the high voltage output. In other words the cap is being used like a small battery to store just enough energy to stop the engine from stalling" But later you wrote:- "The diode is only to stop feeding power the wrong way into the cap thus into the alternator if something is connected in reverse by accident" So I'm confused as to what you want the diode to do. Len |
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WindyMiller Regular Member  Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, The system I am using is a internally regulated 63 Amp Delco alternator. I may refer to it as a generator or an alternator even know the two are completely different machines. So the diode is to allow the use of the frame instead of adding another wire from alt ground directly to the other set of terminals on the cap and the outlets in the box. (I don't understand this point)--- The frame of the whole thing is the return for everything back to the alternator. The diode is to allow power not to be fed backwards into the cap and the B+ stud. This is if the battery is connected the wrong way by accident. Yes damage would be done either way as I have done that already once last winter. Blew the reg and fried my wiring. No the cap was not and is not installed until I know if it will do more damage than good? If I ran an additional wire from the cap to the outlets then the cap would have no effect in the battery charge mode. Simply no connection to the negative battery cable as the converter is not wired that way. I know it does not make sense in the way I am explaining it? I am not good at explaining things sometimes I am affraid. I want the cap to store a small charge to stop from stalling my old engine when connected to a low battery or a heavy 100 Volt load as it stalls the engine sometimes. Yahoo, My hotplate is 750 Watts. I am also going to need a bleed resistor on the cap as it could store the 100 volts which would be bad for the regulator and the battery even know the spike would be a second or two as the cap is switched over into the battery charging mode. Yahoo, My system is 1 wire for the simplicity it offers in the wiring. I have thought of buying a switched mode battery charger from Black and Decker as I had the chance to get a 10 amp charger for $50 but missed out because I could not see the need to buy it with other things needing tending to at the time. Anymore questions just ask? I might have missed something needing clerification. Robert |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
My engine is a Briggs 5 1/2 HP unit that is well over 30 years old I would guess? I have a 6 1/2 inch pulley on the engine to drive the alternator up to 105 volts DC exactly. The old engine simply cannot do any more than that I am affraid. It also has the type of governor that is not really suitable for generator service, but she runs and does a good job most days except for winter months. I guess the way I am confusing Len is because of the nature of caps on a DC circuit. The diode to the frame would cause some kind of a problem I would guess? I must admit that exactly how a cap works on DC confuses me sometimes so I end up confusing you guys. Yahoo, I should just go with a three wire regulator and setup the unit so I can bring the engine to speed then switch in the load to stop from stalling the old girl. However I am really interested in how a simple 1 wire Delco alternator would see or respond to a motor run cap in parallel connection? The crude regulator I posted a link to in page 1 could have something done to make it more suitable and not end up with alot of parts I would hope? I see the article talks of a 0.18 Ohm resistor and an additional diode as over voltage protection? Crude but might just work I am thinking? Any thoughts. To yahoo, yes 1500 watts is a little much for a 63 amp unit, but if I got a 100 amp stator would that make the difference? Alternators of the Delco type are common and cheap here in the US so they are easy to experiment with. Unlike my old favorite the induction generator which requires a suitable motor for conversion and they are rare in my town. Robert |
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| sjh7132 Newbie  Joined: 27/12/2011 Location: United StatesPosts: 13 |
Maybe instead of using a cap to try to store energy to prevent stalling, you should consider some sort of inrush current limiting circuit. I know they make smaller units that are devices with a reverse temperature constant. When they are cold they have a higher resistance, limiting current, then they quickly warm up and become more like a short. (not a perfect short though.) Another approach would be to use a microcontroller and a FET as your switch and instead of slamming the load instantly hard on, it could ramp the duty cycle up over a second or two putting the load gradually on the motor. Steve |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Good morning Robert (well it's morning here) You did not answer the questions I asked in the post above. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
I'll be able to comment on how to connect the diodes once I understand how your system is wired. Would it be possible to put a fly wheel on your engine? This would be equivalent to a capacitor, but would offer the following advantages:- 1. there would be no effect on the electrics. 2. it would store more energy than a small capacitor. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, A capacitor connected to DC is like a water tank. You fill the capacitor with charge just like you fill a water tank with water. Then the cap can discharge and do work of some kind. In your case, supply the energy necessary to supply the welder for a brief period in order to prevent the engine stalling. Water flowing from a tank can do work such as turning a turbine to generate electric power, etc. To continue the water analogy, a diode is equivalent to a one way valve. Water can flow one way, but not the other. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I have attached a modified version of the circuit that was on page 24 of one of your .pdf docs. I assume that this is what you have. I have added 2 diodes to prevent reverse voltages causing damage. D1 needs to be 63A rated. D2 will only have to pass the field current so it can have a lower rating. I initially added a D3 & then realised that it won't do anything, so I deleted it (as you can see near the breaker). If you need to use a capacitor (ie. if the flywheel idea is not viable) then I'll add some simple circuitry to cope with the charging current, etc. Len  |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, The wires 7 and 8 are not used and are tied back. Terminal 9 is not connected to any wires at all. For my alternator wires 3 and 6 are connected together. The engine I have is off a riding tractor and has a cast iron flywheel as do all small engines like from a lawn mower, roto tiller, etc. The pages in the PDF Len is the ones referring to the GM Delco 1 wire alternators. I believe it is pages 4 and 5 in my PDF. The only option I really have is a cap. I have several on hand, but would like to start with the 10 UF cap. I also have a 40 and 50 UF cap. I can also order as large as 60 UF from the surplus center on the cheap. I also want to confirm that installing a proper bleeder resistor on the cap will not cause any problems? This is to bleed the cap fast for changing out batteries to prevent any arching if the B+ cable touchs the frame. Can I also confirm that adding a MOV to the alternator from B+ stud to ground will not cause any problems? This is to arrest any spikes from loads being turned on and off that could harm the alternator diodes. Len, you say the diode near the breaker needs to be a 63 amp? The breaker is only 30 Amp. Or is the diode supposed to be in wire 1 from B+? Len, This system is not used for any kind of welding. I either charge batteries, or use 110 Volts DC for light construction or work around my property. Len, Can you confirm your drawing will if used? Not cause any damage to the system, or interfere with how the switch works. 12 Volts in one mode and 110 in the other? I don't understand the diode in wire 3 and 6 where they are spliced together? I know this must be getting tiring for everyone? But I really do appreciate the help as I am not a electronics expert, but a tinker like most of you guys on here. However I do know the basics and the dangers with DC vs AC and stuff like that. Circuit design is my weak point in this hobby. Robert |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, If you need to use a capacitor (ie. if the flywheel idea is not viable) then I'll add some simple circuitry to cope with the charging current, etc. This is the route I want to go with this. This circuitry will consist of what, some diodes, resistors, ferrit cores, metal oxide varisters? Len, would these work for the diode you said needs to be 63 amp rated? Diodes Diodes 2 These should do for the field diodes correct? Diodes 3 Or do you have any part numbers for parts that would work? I would prefer diodes of the round type that I could just solder and heat shrink into the wiring? However It would probably be better to use a square diode with two legs and screw the thing to the inside of the box for heat sinking purposes. Ofcourse the diode would have to be of the electrically insulated kind as the box is steel and grounded. Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I have put my comments in bold above. Perhaps you should remind me why you need the capacitor. As I said above, I thought it was because you used a welder which has high current damands when you strike the arc. And also when you charge a very flat battery. Please clarify. Len |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I had a look at the diode links. 1 & 2 are transorbs & not suitable. Also it appears that you have to buy more than one. Diode 3 would be suitable for the D2 diode, but it appears that you have to buy 50. However, I'm not sure if what I proposed is what you want, so I won't do any more until you answer my previous post. PS old computer power supplies have high current diodes in them. So, if you can obtain one cheaply, you could possibly remove the diodes. Len |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, I use this setup to recharge two or more batteries for use with a power inverter for loads that cannot use 110 Volts DC. Two of my batteries are large capacity and stall the engine even when it is in full throttle. When I use the 110 Volts DC side I run anything from 750 watts of heating element to a 1HP brush motor. The heating Element and large electric motor tend to stall the engine sometimes. The motor is a pain because it is attached to a water pump and needs high torque for the pump which draws a large amount of amps constantly. Welding is not installed currently but I am seriously considering the idea as I need welding ability for my turbine construction project. So If you want to consider this project as a welder I will go along with that approach. I could use the ability to weld now and then. I thought you said that the alternator can output 63 Amp. yes. I also have a 105 amp stator available for the alternator if I need more amperage. Besides, diode D1 is not in the breaker path. It is in the battery charging path. You said you want to protect against accidental battery reversal. I do. I had this happen last year and it cost me a pretty penny for new regulator and wiring. However, note that D1 prevents the battery supplying the load if the alternator voltage reduces (or the engine stops). Is this what you want? The battery in the 110 Volt mode has to supply the field current for the alternator but receives no charge. I see no reason why this is a serious issue other than the voltage regulator may not like not being able to sense the battery if the current cannot flow from the battery to the alternator via wire 1? I do notice that when the engine is off that there is 12 volts at the outlets when the switch is in a certain mode. The diode would stop the backfeed I would assume? This would be good to stop the thing from draining if the switch is forgotten and a lightbulb is left plugged in by accident. PS old computer power supplies have high current diodes in them. So, if you can obtain one cheaply, you could possibly remove the diodes. I got a ton of these that have Fets that blew up. No problem. 60UF too small? I can get my hands on a high voltage DC cap of around 5000UF if that would work? What do you think I should be on the lookout for? This is the game plan 1. The engine is a variable I cannot change right now. 2. I want to add a cap to stop the stalling issue which is caused by #1 3. My loads are battery charging, Power Inverter, Or heating elements, electric tools, lightbulbs. Welding maybe in the future if I can convince myself that if done with the proper gear is not as dangerous as was distilled in me growing up. Long story! 4. I know that 63 amps in 110 Volts DC the output is only 6 amps or there abouts. I can and will be rebuilding the alternator for 105 amps using new parts and the fan and back half of a 12SI as they have a superior cooling system than that of the old 10SI. This would give 16 amps in 110 Volts Mode. 5. Someday I hope to find a 6HP 3200 to 3600 RPM engine to replace my old 1750 RPM engine of 30 years of age. Engines are expensive and rare around town so I would need to order one and have it shipped in. 6. Caps and diodes are cheap if you know where to look? I know some people who can help and I will be talking to them this weekend. Robert |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, Regarding TVS and such I was told by someone that the caps across the power mains in a switchmode PS do not like 400 Cycles and blowup? If this is the case than what would I need to do to make a suitable surge arrestor for the spiking of the diodes in the alternator? What arrangment of Say TVS diodes, Mov, Or 2x 1UF cap from a computer supply would work to make a nice little surge arrestor for the alternator diode bridge? This is of concern were spikes would be present from welding or the sudden changing from loaded to unloaded back to loaded like with a high power tool? Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Roberet, I have highlighted my questions in the quote in red so it is easy to see my text versus your's. I also added the note re the 63 Amp in red. I have attached some rough calculations on what size capacitor would be required. Note that I did not include the contribtion of the alternator. but I think it is obvious that 60 uF would be next to useless. I suggest you ask someone to check my calculations & assumptions. Len 
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I'm not an expert on spikes from alternators, perhaps someone else may be able to comment. |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I have been forgetting to make some points about the diodes. If you connect diodes as shown in the drawing, this will introduce a voltage drop of 1 Volt or more - depending on the current. This will not make much difference in the 110 Volt case, but it will in the 12 Volt case. So I suggest you consider Schottky diodes in lieu of normal ones. These have a lower voltage drop, but there will be still some effect. Diode D1 will prevent the issue that you raised regarding draining the battery in the 12 Volt case if something is left plugged into the outlet when the alternator is off. Diode D2 will reduce the voltage at the voltage regulator. Is it possible to adjust the voltage regulator to compensate? In other words, can you increase the voltage output from the alternator in order to account for the voltage drop across the diodes? Len |
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