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Forum Index : Electronics : Question regarding capacitors?
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WindyMiller Regular Member  Joined: 05/04/2011 Location: United StatesPosts: 62 |
GidDay All! I have a question regarding the use of oil caps or motor run caps with automotive alternators? My question is this. Would using motor run caps in a circuit with a Delco 10 SI alternator cause the regulator to blow? Does a alternator see a bank of motor run caps as a short? What I have is this. I have a 63 Amp delco alternator that I use for charging batteries and I have it setup so it can supply 100 volts DC for running tools, lights, etc. I have seen on websites the suggestion of using a 10 UF cap to stop from stalling the engine when alternators are used for welders. So I got to thinking and was wondering if I inserted a 10 UF cap in my generator would it cause the alternator to blow the voltage regulator? When a alternator is converted into a welder they remove the voltage regulator and such. I am interested in using the cap method with the alternator to stop from stalling my small engine when I am using this machine to either charge a really low battery or to power a 1500 watt hotplate at 100 Volts DC. This is the projected wiring diagram. The diode is from a microwave. 
Everything on my generator is common grounded to the frame. My second question is this? If the above would indeed work? I would like to insert a 1.6 Megaohm resistor in after the diode as the resistor would not conduct at 14 volts but does for the 100 Volts DC thus completing the circuit. This method is to stop the cap and diode from draining the battery when I leave the unit sit for a week or more at a time. For those that do not follow me please see my other post about Delco alternators. http://www.thebackshed.com/forum/forum_posts.asp?TID=4236&PN =1 Robert |
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| larny Guru  Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, Properly designed Voltage Regulators have overload protection which limits the current (and the power dissipation) if a short circuit is applied to its output. So I suggest that you examine the specification of your regulator. I don't understand the second question as I can't see a diode in your drawing & I don't have the time to read through your other post. Nor can I see why you think the resistor would not conduct at 14 Volt. Len |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, The regulator I am sure has a specification sheet? But I have not found any official documents from Delco? I am unable to obtain that information? The diode in my drawing is the little black square. The resistor I would assume does not conduct because I have one on a meter and it does not move at all until higher voltages are reached. As I understand it you are basically saying the cap would be seen as a short in the circuit? Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, Can you open the case of the regulator and look inside? If so, you should be able to see the regulator IC (if it is an IC - it may be a discrete one) Tell me the numbers on any ICs or transistors that you can see and I'll have a look at their data sheets. You can't have a diode in series with the battery. When the battery is charging, the current goes through the battery and through the "black blob" from Right to left. But when it is discharging,the current goes from the battery, through the load and through the black blob from Left to Right. So if the blob is a diode, it will either block the charging current or the discharge current - depending upon which way it is oriented. Also, if you have 14 Volt across a 1.6 M resistor, the current will (using Ohm's Law) will be 14/1.6 = 8.75 uA. If the capacitor is discharged and then you apply a voltage across it, it is almost a short circuit initially. So the initial current will be very high - unless the regulator has overload protection to limit the current. It is almost certain the the Reg has some type of overload protection. There are broadly 3 types of protection. 1. current limiting 2. fold back 3. electronic fuse or physical fuse. Long story, Len |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
The only regulator I have is the one in the alternator. I cannot easly disable my generator to remove the thing and pry it apart. I actually blew up the regulator by accident once while hooking the battery up as I got in a rush and connected in backwards. I fried my wiring and the regulator. However I did not keep the old one so I cannot use it as a reference. However I did find this on the web while looking for a way to repair the thing. This regulator is almost exactly like the original delco unit. Regulator I was shocked to see that it was almost identical to the way the delco units are built when I was comparing the two side by side. The wiring in the drawing is like this. The red wire comes from the alt into the cap, from the cap on the same side of the cap the wire continues on to the load which is either the battery or the output for the 100 volts DC depending on the switch position. The diode is not in line with the battery on the positive wire. The diode is only the connection from the other side of the cap to ground through the the steel frame of the generator. Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, A picture is worth a 1000 words. I drew the attachment from my understanding of your description, but it does not make any sense. So I must have misunderstood something. The problems with the drawing are:- 1. The alternator can be switched either to the load or with S in the other position to the battery. The battery can never supply the load. It is usual for the battery to be across the load so it supplies the energy when the alternator is not operating. 2. If the diode is as drawn, then the cap can charge, but never discharge. If the diode is oriented the other way, then it can discharge but never charge, Of course, if it can't charge, there is no energy stored so it can't discharge either. I looked at the link. Comments:- 1. The voltage regulator is a crude design. The voltage at which it switches ON/OFF is dependent mainly upon the Zener voltage which will vary a little from one Zener to another since all components have a tolerance. 2. It would be temperature dependent so the voltage at which it switches will vary a little with temperature. EDIT. It does not have any overload protection. What I think you need is a well designed voltage regulator with current limiting so the capacitor can charge slowly and thus store the energy necessary to prevent the stalling of the engine when welding that you mentioned in the first post. Len 
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len this is basically what I have done with my alternator Alternator Modifications I use my generator either to charge a set of batteries to run my inverter for AC power, or I use the 110 volts DC the alternator produces to run tools, lights, electric heating elements, etc. My inverter is just a cheap 700 watt mod sine I use for a small TV and Digital signal converter box as our antenna signal here in the USA switched to digital not long ago. I also run a VCR or DVD player some times as well. This generator allows me to cook something to eat and run the TV during bad weather like the hurricane that went through a few months ago. The idea with the cap is this. The red wire is from B+ and goes into one side of the cap. The other red wire comes from the same side as B+ but goes to the switch in the box. 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. 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. 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 as it is old and tired, but a good work horse. Robert |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
I am thinking the only way to solve this is to go down to the wrecking yard and get a 35 amp Delco just to try this idea incase it blows up the alternator. That way it was not the 63 amp unit and would be no big loss. Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, I sent you a PM. I'll await your email. I need to fully understand your arrangement & what you're trying to do. So don't bother going to the wrecking yard at the moment. Once I understand the situation, I'll be able to advise you better. Len |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, It all works like this. Inside the Power converter box is a simple 4 pole double throw switch. wire 1 from the alternator goes into pin 1 on the switch, a little orange wire is also connected to wire 1. The little orange wire goes into a 30 amp circuit breaker and to the outlet. The outlet's neutral is the frame of the generator to the case of the alternator. On the switch wire 2 goes to the battery. Wire 3 and 6 are connected together. Wire 4 and 5 go to the triode pack and the voltage regulator. Wire 4 is connected to the triode and 5 to the voltage regulator in place of the steel strap. When the switch is thrown the alternator field is excited with 12 volts dc, the regulator is isolated, and the battery disconnected from the B+ stud. The B+ stud is connected to the outlet in this mode and when at 2500 RPM presents 100 Volts DC. In this mode the battey is only supplying the field and is receiving no charge. What I propose is simply connecting a cap in wire 1 from B+ to the switch. The cap would have one side connected to the black wire 1 and the other side to the frame in place of a copper wire so the cap would be in parallel with the alernator and either the battery or the outlet depending on switch position. The whole way of thinking I have is this. The battery negative wire is connected to the case of the alt. The outlets in the Pow'r converter box is connected to the frame of the generator and thus the case of the alt. If I connect one side of the cap to the frame it should work with either mode using the frame as the white wire for parallel connection. 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. On The cap between the terminals is also a bleed resistor and on the case of the alt a MOV is installed from B+ to the case as a spike arrestor to save the diodes in the alternator. In the high voltage side the regulator is not connected and would be no problem with the cap. The only problem I see and need a answer to is wether or not the crude delco voltage regulator would see a parallel cap as a dead short in a dc circuit? Robert |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Robert, The regulator in the link you posted does not have any over current protection. So it is likely to be damaged by the capacitor charging current. I need to see the full picture so I can suggest a solution. Len |
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| sjh7132 Newbie  Joined: 27/12/2011 Location: United StatesPosts: 13 |
10uf is nothing. 63 amps would charge that at a rate of 6,300,000 v/sec. In other words even if it did look like a short it would only look that way for a millisecond or so. I'm guessing that your alt wouldn't even notice. And this only happens if you connected the fully turning alt to the fully discharged cap. Isn't it more likely the cap will charge as the turbine spins up? Steve |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
I agree, but my assumption has been that you will need a lot more than 10 uF to achieve your aim. I suspect that you will need at least 5000 uF. |
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| sjh7132 Newbie Joined: 27/12/2011 Location: United StatesPosts: 13 |
Even if you made it a farad, it would charge at 63v / second. Is it standard practice to let your turbine / motor and alt spin up, then connect the load? That sounds bad to me for several reasons. If the load is always connected to the turbine / motor, I don't think it could accelerate fast enough to hurt the alt. If you really want to switch the load on and off, do it after the cap. BTW I'd suggest in the circuit that the diode go between that alt and the cap. Where it currently is (between the cap and ground), I think it will prevent the cap from putting current into the load like you want. Steve |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Another issue to consider is whether the capacitor can withstand a current of 63 Amp. There is no point in connecting a diode between the alternator and the capacitor since the alternator is connected via a diode bridge anyway. As I said in a previous post, and diode between ground and the capacitor will either block the charging current or the discharging current depending on which way it is oriented. Len |
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| WindyMiller Regular Member Joined: 05/04/2011 Location: United StatesPosts: 62 |
Len, I see what you are saying, and will agree with it. The diode method is scrapped for reasons stated above. However I was under the impression on a DC circuit the current would flow from the alt into the cap and through the diode to gound since DC does not have the sine wave like AC does? I thought DC went in a streight line. The cap would charge from the red wire and discharge through the cap and diode to ground? The cap I am thinking of using is a AC oil cap, other wise known as a motor run cap. These caps have been used for decades with induction generators putting out some serious amps and I have never seen any reports of them failing? Steve, This setup is not being driven by a turbine at all. The whole thing is coupled to a petrol engine. Robert |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Robert, The capacitors in a small engine welder give you enough extra energy to strike an arc. For a fraction of a second it is a dead short, before the rod starts to melt, without the caps the alternator can stop dead. when the arc is lit the operator controls the resistance with the arc size, distance and angle of the rod tip from the job, which in turn effects the voltage and current the alternator delivers.In a single phase DC welder the caps smooth the choppy current so that the arc wont snuff out at a low voltage point in the rectified wave's cycle. With battery charging the problem is a constant heavy load on a cold grumpy engine or the sudden load from nothing (to quick for the governor to catch up) stalling the motor. Capacitors will not be effective unless they are massive. Is the delco alternator you are using a 3 wire model or one wire? this is a three wire internal regulator. 
If it is the 3 wire option, one of the spade terminals is a remote voltage sense wire. manipulating the voltage that the regulator is seeing on this wire will change the voltage applied to the rotor field coils which directly effects the alternator output. A suitable diode or resistor on a switch on this cable will give you a choice of two charging rates and the ability to charge the batteries to a higher voltage. Reducing the charge voltage(and therefore current)is a bit trickier. There are two options, boost the voltage seen on the sense cable (may need an amplifier circuit for this). Or manipulate the voltage on the regulators earth strap by inserting a diode. Both will have the same effect. This is a mod to change the earth voltage on a bosch regulator but only suitable for very light duty, the diode is not big enough to be reliable for heavy use. You can clearly see the earth strap to the bolt hole has been cut and removed and a diode soldered in its place. 
CHANGING REGULATOR EARTH VOLTAGE On an external regulator it is easy isolate the regulator from earth and fit a switch to the ground terminal with a diode that can handle the field current and this will change the earth voltage by 0.6 volt. The diode will need to cope with the full 3-4 or 6 amps across the field coils depending on the charge rate and perhaps need an insulated heat-sink to dissipate the excess heat. On the internally regulated delco the earth strap from the regulator is one of the three bolts that hold it in. It is very hard to do this mod without mounting the reg outside the alternator casing and running wires in to the connection points. Ideally you should end up with 4 settings 1 no power (open circuit field wire or regulator earth) 2 low 13.6 Volt? warm up and trickle setting (diode on regulator earth) 3 standard 14.2 volt (sense wire directly to the load) 4 boost 14.8 volt (diode or resistor in remote voltage sense wire) the low settings current output will be directly affected by the batteries resistance at that particular voltage so gels and wet leads are different. Hope this makes sense, if not, I can post a couple of photos, as I am repairing one from a John Deere tractor soon. yahoo PS there are some diodes that will give a 1.2 Volt drop. PPS not all alternators are wired this way so it is not a universal modification. thermal runaway is a real risk for the batteries and alternator without temp sensing in the circuit. I'm confused, no wait... maybe I'm not... |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
yahoo2, Thanks for the input. Do you have a circuit diagram of the arrangement? I'm trying to help Robert without any prior knowledge of this arrangement. Len |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
bit embarrassing  the diode on the earth strap will raise the charging voltage Sorry I had a major Brain Fade.
the only options to reduce it are, wiring the remote sense wire directly to the alternator output and placing some resistance (like under floor heating cable) in the main cable or boosting the voltage artificially. couple of links SmartGauge Electronics - Increasing alternator charge voltages Self build adjustable alternator controller I will have a look for a circuit diagram, I might not have it on this computer, it would be more than 12 years since I last modded a delco. The professionally built engine driven chargers have two adjustable external regulators set to different voltages and a 3 way switch. yahoo I'm confused, no wait... maybe I'm not... |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Given the choice I would I would run a standard AC battery charger from the 100 Volt dc supply See warpspeeds post in johns microhydro discussion. (about half way down the page) Flat batteries are best charged up with a shop charger, not a car alternator. And the hotplate, 1500 watts is about 500 over the alternator's limit so it is going to struggle no matter what. yahoo I'm confused, no wait... maybe I'm not... |
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