home made 12 volt generator

[DrivingMissLazy]

I do not know the date of the supplement, but the 4104 was built until 1960. In my statement I said in the 50's 0r 60's. I know that in my 53 model 4104 it was a generator. Sometime then according to what you posted the silicon diode and transistors were developed in the 50's for commercial use and the alternator was developed.
The first computer ever built I saw in 1954 (Philco Geniac) and it was still all vacuum tubes. Therefore I still stick to my statement made in the earlier post: The silicon diode was not invented until the 50-60's and the brushless alternator was not possible without the diode.
Richard

[niles500]

As an aside - I previously verified that the most efficient conversion from AC to DC was by using a full wave rectifier resulting in a 30% +/- inefficiency - FWIW

[Stan]

I was in electronic school in 1956 when the school received a germanium signal transistor from RCA Labs along with a blurb of how these would revolutionize electronics.  I repaired quite few voltage regulators for buses, and still in the 70s they were using germanium transistors that were only available from a small after market company who had them custom made.  Likewise, the front wheel driven speedometer that MCI was still using on the MC-7 (1973) was all germanium transistors. I was using power diodes (20 amp) before 1960 which I suspect were germanium because more than half were reject because of low back resistance and very large heat sinks.

The development of the silicon junction after that time did revolutionize, not only electronics, but the entire world.

I worked on one 1960 4104 and it incorporated quite a few things (including an alternator) that had been developed for the 4106.

Niles: Do you have a reference for those numbers of 30% efficiency. I find it hard to believe that a 270 amp, 28 volt alternator would be radiatiing over 5 kilowatts of heat from the diode plates when it is running. With that kind of efficiency, you coud use an air cooled alternator to heat your bus with the hot air. Since the diode plates are insulated from the case and have no colling fins, I doubt that they radiate more heat than a 100 watt light bulb.

[DrivingMissLazy]

I also would like to see that. My belief is that they are over 99% efficient.
Richard

As an aside - I previously verified that the most efficient conversion from AC to DC was by using a full wave rectifier resulting in a 30% +/- inefficiency - FWIW

[niles500]

Sorry I was wrong - its 81.2% - I must have been confusing it with another application

the math is on the following link - HTH

http://72.14.203.104/search?q=cache:OosJkJDnq40J:www.visionics.ee/curriculum/Experiments/FW%2520Rectifier/Full%2520Wave%2520Rectifier1.html+full+wave+rectifier&hl=en&gl=us&ct=clnk&cd=5

[DrivingMissLazy]

OK. That is the efficiency of the complete AC to DC circuit including the transformers and other components. I suspect the loss across the diodes is less than 1%. I am still surprised that the overall conversion efficiency is that low though.
Richard

Sorry I was wrong - its 81.2% - I must have been confusing it with another application

the math is on the following link - HTH

http://72.14.203.104/search?q=cache:OosJkJDnq40J:www.visionics.ee/curriculum/Experiments/FW%2520Rectifier/Full%2520Wave%2520Rectifier1.html+full+wave+rectifier&hl=en&gl=us&ct=clnk&cd=5

[Stan]

On a silicon diode rectifier, the only loss is the voltage drop across the diode junction. This is nominally .5 volts on an ordinary silicon  diode like we are using.  On a three phase full wave bridge rectifier this loss occurs across two diodes for each phase. One volt of loss on a 28 volt alternator represents 3.5% of the voltage but since the loss occurs at the peak of the waveform where thee is very little arrea under the curve, the actual total power loss (p in/p out) will be less than the 3.5%

Nothing in this world is 100% efficient so any other component that you introduce into the circuit will introduce more losses and they all multipy in series. This is the big advantage of the three phase rectifier in that no other components are required to get a DC voltage  higher than the RMS voltage of the AC input, without having to add a ton of capacitance.

[Tim Strommen]

...Your making this more difficult (for me) than it needs to be.... My understanding when I started this thread was that you could make a generator of sorts using an alternator and just charge your batteries to keep up with the demand on them from the inverter. eliminating the need for a large, expensive, and loud generator. I already have a coleman 3500 generator that does the job when called upon. I however cannot use my smart charger off of it as it has already burned up 2 of them. Just not compatible. I may build one of these just for fun and something to do and the learning experience....

No matter what anyone else thinks, I think it's cool, Ron.

My plan is to use inverter technology and an Isuzu motor from a Carrier or Thermoking reefer unit. It'll take up a whole bunch less room than my old Generac contraption. I also plan on mounting 2 Leece-Neville truck alternators on it to run 2 seperate inverters. After all, why not, If the little motor has to run, it needs to be run under a load anyway, why not make that load as heavy as possible?

Hey Ron,

Your idea is totally valid.  Take a look at the small Honda generators, the new hybrid-drive systems in use, and the diesel-electric locomotives that the majority of railroads use.

On smaller generators - a small microprocessor can control the speed of the engine to create enough power out of the generator (rectified alternator) to fit the demand of the load - the DC is then inverted to AC for consumption.  This is the type of method is used in the little Honda inverter generators.

For hybrid-drive systems, they use a smaller engine and a battery/ultra-capacitor bank to store power when the drive train load is not high.  Then, when the load is increased, the batteries/ultra-capacitors dump their stored power into the drive system to augment the power created by the prime-mover (this allows the use of a smaller prime mover to overcome the "average" load - not the "peak" load a direct drive vehicle needs to support).  When the load is near-or-at "No-Load" for a given time, most new hybrid drives will shut down the diesel to save fuel (and will run from the batteries until they reach a low level).  Diesel-electric locomotives are run about the same way - except there is no mechanical connection to the drive wheels from the diesel.


Back when I was toying with the electric fan replacement concept (which worked somewhat - but not to my satisfaction), the idea was to have a second power pack to run the house and maintain the chassis electrical (and take over for the prime-mover alternator when on hills etc.).

I quoted Dallas' comment as he has hit the efficiency nail on the head.  If you are going to be running a secondary engine - you'll want to try to snatch as much energy out of that engine as possible.  Electricity is okay, might as well throw on an air compressor to keep the chassis aired-up, and heck why waste that heat generated by the small engine?

One of the ideas I was floating (and continue to...), was using a DC generator to maintain the chassis battery bank, and separately run as much of the interior as possible (using 24-volt devices as much as possible) on a second alternator/battery bank.  A 110-volt AC inverter only runs the microwave and the cook-top.  Having a 24-volt coil in a water heater (hydronic heating throught the whole rig - and a heat exchanger to warm the prime-mover's block before starting) - then using a heat exchanger to the water heater to reduce the electrical load of the coil, and an exhaust heat exchanger to grab more heat from the output of the small engine (a marine heat exchanger for this).  By having more than one source of energy put into a specific task - it ensures optimal efficiency, and shortest run time.  While the engine is running, piping in a second air compressor to the govenor line and T-ing off the output line to the air dryer ensures that any running engine produces air pressure automatically to keep the tanks full using the existing controls/filters (makes for quick getaways...).

There was a busnut on the other BBS who had contacted me about building a controller for this type of task - but admittedly I've been side-tracked with work (so sue me - I work in the Silicon Valley at a technology company).

Basically it would monitor a buch of things and determine the optimal time and durration to run a secondary power plant (SPP) - and maintain the vehicle within a certain margin.  There was an air pressure tranducer planned to kick on the SPP if the air was below 30psi while the rig was in-station, a prime-mover water temp sensor planned to help warm up the block before starting (you know how those ol' DDs hate real cold), and a battery monitor to ensure the batteries didn't go below their 25% discharge level (and a load current sensor to ensure the SPP was running when a major load was being run - like a 1500w microwave off an inverter).

A small micro-controller would have the operation characteristics for each system plugged into a table - which would be used to run the engine at the RPM needed to maintain a little head-room over the applied loads.  It would also provide a safety system to shutdown the SPP if there was a problem (fire, low oil, low water - danger of using too much fuel from the main tank).

I presume a system like this can also include an air-conditioner compresor to help with cooling/refridgertion.  Basically, if you try to consider how you can tie a few systems together it will give you more bang for your fuel buck.

Cheers!

-Tim

P.S. - It's a little more complicated putting in a second alternator - as you need to ensure that they don't interfere with each other's operation.  A simple pair of relays to "lock-out" the voltage regulator/field on the oposite alternator should be enough to protect the electrical system and components.  This can be accomplished by using a pair of double-pole double-throw relays - and wiring the positive supply of the coil of the oposite relay to one of the poles (on the Normally Closed side) and the ignition sense of the local voltage regulator to the other pole in the Normally Open side).  So when the first power plant is turned on, it energizes the local relay's coil which breaks the connection to the other power plant's relay coil - while attaching the ignition sense on the local v-reg to the supply (turning it on, and operating the local alternator).  Even if the other power plant is turned on - the other relay can't be energized because the coil has no supply power (circuit broken by the first relay) - thus the other v-reg/alternator will not be activated.  But - when the first one is switched off - the first relay opens reconnecting the other coil's supply, allowing the second power plant's relay to now be energized, and thus turning on the second v-reg/alternator (and of course locking out the first one).

This way - the first alternator will always be activated - and the second will not interfere with the first's operation.  It's a simple bi-stable break before make lock-out safety system.

Alternatively, you could use a Normally Closed single-pole single-throw relay to simply lock-out the secondary alternator (by breaking the v-reg's ignition sense line) when the prime-mover is running (simpler).

Oh and in either case, if you have more than one alternator per power plant (say one for a house bank, and one for a chassis bank), you don't need larger relays with more poles - you simply split off the ingnition sense from the respective relays. -Tim (confusing enough? )

[gus]

Well, actually the old auto generators produced AC, all generators do. The reason it came out DC was that only part of the output was used. One half the alternating current was clipped off by using only a few of the armature segments and what came out was sort of a pulsating DC but good enough for auto use. Then it was pulsed by ignition points so  the coil (which is a transformer) could raise voltage high enough to fire the spark plugs!!

Alternators produce AC (!!) but are rectified by diodes to make DC. Again, only part of the output is used.

Kind of sounds like what started this thread in the first place.

[Homegrowndiesel]

Hey CR,

The only reason my Homemade DC Generator is loud is because it is on display, without any shielding, or sound control.

YOU CAN DO IT.


I feel the bigest efficiency comes from the direct drive of the air conditioning compressor, recapture of the exhaust gases, and cooling system recapture of thermal energy. You can make DC with less fuel used(low idle), you can store DC not AC.

I am going to try to recapture the heat generated by the alternator and use it.

Lets take the mechanical engine output, figure loses in conversion to AC 120, or 240. Now take the losses of conversion of the electric motor that drives the electric - mechanical, compressor.

Direct drive belts take 2-4 % , much better than -40, -40 mechanical to electric - electric to mechanical compressor.

I could not cite the proper text book losses, but have found more comfort for less $ and foreign oil used.

OW, sorry I did not mean to hijack your thread. Just add to it.

I would use a 24 volt system if my bus was 24 volt.

Yea I like the vrod approach. I thought a Harley engine would draw some attention. Liquid cooled is a must. Easier to recapture the thermal energy also.

With the 5, or 6 speed trans you could easily choose the ratio to efficiently drive air conditioning, electrical generation, and an air compressor.

I would be willing to help.

Bill

[captain ron]

 

Hey CR,

The only reason my Homemade DC Generator is loud is because it is on display, without any shielding, or sound control.

YOU CAN DO IT.
Yea I like the vrod approach. I thought a Harley engine would draw some attention. Liquid cooled is a must. Easier to recapture the thermal energy also.

With the 5, or 6 speed trans you could easily choose the ratio to efficiently drive air conditioning, electrical generation, and an air compressor.

I would be willing to help.

Bill

It may take a while to find an affordable V-Rod engine and transmission as they are still too new not a lot of salvage. but I will find one and build this. It will be fun, cool, different and a great conversation piece. And when I find all the HD components I will call on you for your offered help. I keep watching E-Bay and Crashed toys .com and will put a bug in my friends ear that owns the HD dealership

[Jeremy]

As per my earlier post on this thread, I very much like the idea of a simple 12v / 24v DC generator for use as a supplementary battery charger; personally it would only be for use as an emergency back-up as I already have a full-size silent generator for 240v mains voltage (and also, as it happens 12v DC, but only at 8 amps).

I've been looking through the catalogue of my usual supplier of workshop machinery, and I see that 4-5hp Honda petrol engines are far cheaper than I would have expected, and they are ready-to-go with pull-start, fuel tank, varous drive pulleys etc. I realise these will be noisy and shakey little things, but for my application (ie. emergency use) they would be ideal. Carrying petrol isn't really a problem for me as my full-size generator is petrol (yes, I would have preferred a diesel genny, but petrol option was much smaller, quieter, lighter and cheaper for the same output).

As well as various low and high voltage alternators, the same catalogue also includes lots of other devices that the engines can be bolted to, such as air compressors and various types of water pump, including jet-washer pumps - it's a shame I cannot really think of a good use for any of those things on the bus.

I still think my earlier idea of using the back-up engine to somehow drive the OEM bus alternator would be the perfect solution, but I also like the idea of using two small and cheap 12v car alternators rather than a heavy and (probably) expensive 24v one. My house batteries are 12v, so there would be benefits there too.

I couldn't help but wonder why I hadn't come across petrol-powered battery chargers / DC generrators before, given that they seem such good idea. I did a quick search on Google, and the first result that came back was of this unit from Australia:



In order to choose an engine to power such a generator / charger I would be very grateful if someone could offer a clear explaination of how to calculate the engine horsepower required to turn an alternator (or alternators) of a given output. Presumably, if the efficiency of the alternator is known it should simply be a matter of converting mechanical power to electrical power? Also, what is the optimum rpm for a car-type alternator? I've always assumed their power output was very flat over a wide range of engine rpms, but presumably there is a speed they are typically most efficient at. I can work our the gearing required between the engine and alternator myself.

Lastly, I very much like the idea of the engine throttle being automatically opened and closed as the load on the alternator varies - in fact my full-size generator has this feature and it is a major benefit. Can anyone think of a simple way to acheive this? Designing custom circuitary to operate servos or stepper motors is beyond me.

Jeremy

[Tim Strommen]

Shoot - I just spent 30 minutes writing up a big long explanation of how this is done, and then pushed some funky keyboard combination and lost the whole post by going "Back" (GGGGRRRRRRR  ).

Oh well (the milk is spilled) - I'll try a truncated version.  You'll want to have these four equations handy:

Watts = Volts X Amps
Drive Ratio = Alternator RPM/Engine RPM
1KW (1,000 Watts) = 1.34102209 HP
Horsepower = Torque x RPM / 5252

There is also a rule of thumb you'll want to remember: Assume a 20-25% loss at every conversion.  This would be mechanical-to-electrical like in an alternator – and even mechanical to mechanical like in a belt drive (some belt drives can be up to 98% efficient, but if they are not maintained can drop to 92% or less efficient – in my opinion I'd play this one safe).

You'll want to start at the alternator as it's the last conversion (I'm disregarding wire "line" loss for this discussion as it should be part of the system design equations already ).  Make sure the alternator you pick is sized for the system and charge-rate of your system.

For this example – I'll assume we're using a 24Volt (28 volt charging voltage) 200Amp alternator which is belt driven.  Also – I'll assume that the max current is achieved at 6000RPM (this information would be in the alternator's spec-sheet).  This means that the alternator will create 28Volts x 200Amps = 5.6KW at the output posts.  However this is a result of a mechanical input shaft to electrical field conversion.  Which means – you'll be drawing 5.6KW x 120% (added 20% of loss to the output power – or a decimal value of 1.2) = 6.72KW at the pulley.  If you don't have an engine that'll put out the required HP at 6000 RPM ( or you don't like the "sound" {punn} of an engine running at 6K RPM for any length of time) – then you'll need to use a step-up drive system (belts are typical).  So let's add another "loss" to the system: 6.72KW x 1.2 = 8.064KW.  This number will let you do two things: 1) pick an appropriate peak output engine, and 2) a suitable drive system.

To pick the engine, convert the KW to HP (KW x 1.34102209 = HP) so: 8.064KW x 1.34102209 = 10.814HP.  You'll need to pick the next size UP from this or you'll stall out the engine at max load.  Let's say that we have selected an 11HP engine.

To pick the drive system – you need to figure out the max power and RPM of the engine from the published performance table.  Now figure out the pulley size by measuring the alternator pulley size and getting the circumference (let's say the alternator has a 2" diameter pulley).  The circumference of our alternator pulley is thus: Pi x Diameter = Circumference or Pi x 2" = 6.283" circumference.  Now figure out your required drive ratio by finding the RPM at which your engine creates just a bit more than the peak power required (we'll say 11HP in this case – and for this example say that the hypothetical engine's performace table indicates that this occurs at 2600RPM).  So your peak output of the alternator (28Volts@200Amps) occurs at 6000RPM on the alternator and the 11HP is generated at 2600RPM.  So find your drive ratio by 6000 / 2600 = 2.308:1 (or 2.308 rotations of the alternator for every 1 rotation of the engine).  To find the size of your engine (drive) pulley – take your drive ratio number (2.308) and multiply it by the alternator pulley circumference (6.283"): 2.308 x 6.283" = 14.501" engine pulley circumference.  You can get your pulley diameter now by reversing the math: 14.501" / Pi = 4.616" diameter.  You'll also need to ensure that your drive system can support the power rating for the length of time it's being used (i.e. 11HP under continuous use).  Some systems will require the use of a dual slot pulley (or worse if really big).  You also need to ensure your engine can support the side-load of the tension of the pulley/belts against the crankshaft bearings (or the engine will fail pre-maturely).  You may need to use a short shaft and a set of pillow blocks (aka bearing blocks) to take up the belt load from the engine.  Just be sure to align your pulleys so they don't eat belts quickly.

Both your selected engine and selected alternator should come with performance tables showing (for the engine) how many HP are generated at a certain RPM – and (for the alternator) how many Amps are generated (at the charging voltage) per input RPM.  You'll need to match up values of the alternator to the values of the engine.  This is easily done within a look-up table in a microprocessor (and you'll probably need one to controll this well - as most of-the shelf voltage regulators are not suitable for this task).  You'll also need to get the table for the field current of the alternator to the output amps.  Again – plugging these into a microprocessor's look-up table is easy.  A voltage sensor can tell the microprocessor if the voltage is below the nominal rating (less than 28V because of draw-down) and increase the RPMs of the engine.  A smart-desiner's voltage regulator can also prevent the field from getting a bunch of current until the engine is at an RPM where it can support the requested current (a fractional multiplier equation [to derive a "margin"] will ensure that the engine power [throttle] is always that fraction above the actual requested alternator load - and then only allowing the requested output to be so-output in relation to the >>actual<< engine RPM via the look-up table will prevent a stall).

By adjusting the multiplier (engine HP to Alternator output "margin") you can affect the rate at which the engine will obtain it's desired RPMs.  If you want to get more complicated - you can vary the magnitude of the multiplier over the base value (with another multiplier) by evaluating the difference of the requested current in relation to the actual output current.  This way it will push the engine up faster if a large load is detected - but will only rev up the engine slowly under light loads (rate of acceleration affects fuel economy - and if it's a light load, it's more likely it won't negatively affect the battery pack's charge state with a huge draw).  This would probably be optimal, as allowing the batteries to take care of long term variations in smaller amplitudes will stabilize the system faster.

This system can be further improved with load current sensors (current loops or a shunt) to tell the microprocessor exactly how much power is being drawn from the alternator (and even another to show the ammount and direction of charge/discharge from the battery) – which will give it a better picture of the power situation in-circuit.  For example – say you turned off your 2400Watt inverter and now there is no draw on the alternator other than the trickle the batteries need – the shunt will note this change quickly and the voltage regulator can drastically cut the field current to the alternator to prevent a voltage spike, keeping only the trickle charge to the batteries.  Also battery and ambient temperature sensors can be used to better match charging rates to the current battery states (and with a microprocessor controlling the alternator - you can do those fancy multi-stage charging steps).

If you have the microprocessor running the engine and watching the system voltage/current already - you may as well put in some other features like engine warm-up before loading, engine cool-down before shut-down (required for turbo longevity if one is used on your engine), low-oil shut-down, over-temp shut-down, low-fuel shut-down (if the generator and Prime-mover are run from the same tank), auto-start, auto battery-maintain, "quiet time" (hook up a clock and set an "out of bounds" time-frame when most in your camp ground are sleeping...), battery fan controls, etc.


Of course building your own voltage regulator is a bit complicated, and making a mistake, and/or not having hard fail-safes (fuses, voltage limiters, diodes, etc.) can destroy very expensive parts in short order (say a $3000 inverter? or a large battery bank?).

It's not for the faint of heart – but it can still be done with a good deal of planning.

Heck – diesel locomotives use a similar control system to regulate the speed of the engine/generators – and Honda has produced small A/C inverter-generators that do this all the time (so it has been done, and can be done again).

Do it your way – and be safe (put in emergency shut-downs and fire/smoke detectors), there's nothing worse than burning down your bus with your family in it... 


Oh - almost forgot.  If you use a current shunt on the output, it creates a voltge across it.  If you tap in a low-voltage solenoid/actuator to the measurement lugs of the shunt - the voltage could theoretically push the solenoid out harder/farther with a higher load.  Attaching the output shaft of the solenoid to the throttle is the easiest way I can think to automatically control the speed of the engine based on the load - but this would have to be coupled with an anti-lug govenor (which I think most small engines have in them anyway).  Sounds complicated and hard to ballance - mostly because is is .  Manufacturers who use this method have custom actuators and throttle springs for this function.

Another concept that I've not seen but is concievable - is to drive and actuator from the voltage regulator's field output (more field current - equals more alternator load, and should be matched with more throttle movement) - this could possibly stabilize a generation system faster (but don't quote me on this ).

Cheers!

-Tim

P.S. Hope this wasn't too long-winded and boring...

[gr8njt]

^^^^^^^ ^^^^^^ That's what I'm talking about.^^^^^^^ ^^^^^^^
THE ABOVE POST BY TIM STROMMEN IS AN INFORMATIVE, INTELLIGENT AND  WELL ARTICULATED SCHOLARLY POSTING.
You sir, have placed in a "nutshell" the most important "basic" factors to consider needed to plan such an interesting project (though not for the faint of heart) without the "confusing micro-details" that would have earned me a PhD in a few more weeks. The exact calculations and formulas that you presented to derive at correct equipment combinations is the first in this board, bar none.

TIM STROMMEN, You are an asset to this community. The substance of your post exceeded all expectations in this thread. I salute you!

[Tim Strommen]

Hey Gr8njt,

    Thanks for the note , it was rather entertaining to read (and all this after the thread almost got away from Captain Ron).

The accidentally deleted post I wrote previously may have given you the extra edge to get that PhD  .

Cheers!

-Tim