Need circut to convert 14v car alternator to 12v fixed with 20A

Thread Starter

hamed_hossani

Joined Dec 25, 2020
2
Hello;
I'd like use car alternator to power on hashboard asic miner(l3+ 800w that ha 4 of them and any of them got 250w)
The car's aletrnator output is 14v
I need circut for convert 14v to 12v for power on the hashboard. That runs by 12v 200w.
My idea is generate electricity with mown engine. Whitout use convertor 12v dc to ac 220. I would like to use 14v for power on asic directly whitout power modules. (220v 1600w)

Can i use Atx (pc power psu) to convert 14v to 12v with 20A or higher? I need a circut for this convert. For lower cost. My asic has 4 of hashboards.
Are the voltage and Current damage the hashboard?

Is it possible?
What is your proposal?
 

Leadfootin

Joined Nov 8, 2019
29
Simplest solution is to not modify the alternator but connect a very large capacitor like 1F or more on the output. Then measure voltage and use drop diodes or a simple low drop-out voltage voltage regulator circuit to get a stable output at 12V or exactly what you need.
Beware that some alternators may not play well with this setup. I would get one of the older self excited Delco one wire alternators as they contain a robust regulator and no external power is required upon start up. That big cap is an absolute necessity as you are looking at about 20+ amps current needing the voltage ripple to be reduced to within the regulator's capability.
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
You can remove the regulator and fit a field control circuit I have used once using a LM311 and a Mosfet and set the comparitor for 12v, you need an initial 12v supply to start the regulator.
After that is is self sustaining
Max.
 

Leadfootin

Joined Nov 8, 2019
29
You can remove the regulator and fit a field control circuit I have used once using a LM311 and a Mosfet and set the comparitor for 12v, you need an initial 12v supply to start the regulator.
After that is is self sustaining
Max.
As long as the ripple voltage can be kept low enough for the circuit being driven. Alternator output is rectified three phase and some regulators chop the field drive rather than linear control so output waveform must be checked.
 

bassbindevil

Joined Jan 23, 2014
158
I'd modify an external regulator (or make one). But be careful that the alternator can handle that load continuously. Look for an extra heavy duty unit from an ambulance or truck, and provide plenty of air cooling.
 

Patel N

Joined Nov 15, 2019
1
Hello;
I'd like use car alternator to power on hashboard asic miner(l3+ 800w that ha 4 of them and any of them got 250w)
The car's aletrnator output is 14v
I need circut for convert 14v to 12v for power on the hashboard. That runs by 12v 200w.
My idea is generate electricity with mown engine. Whitout use convertor 12v dc to ac 220. I would like to use 14v for power on asic directly whitout power modules. (220v 1600w)

Can i use Atx (pc power psu) to convert 14v to 12v with 20A or higher? I need a circut for this convert. For lower cost. My asic has 4 of hashboards.
Are the voltage and Current damage the hashboard?

Is it possible?
What is your proposal?
very cheap idea is IC 7812 USE IN PARALLEL IN NUMBER OF AMPERES each IC serve 1.5 Amps and it must be mount on Good heat sink. at alternator out put link 10000mfd cap 25v .
 

Leadfootin

Joined Nov 8, 2019
29
In addition to Patel's reply, use a single adjustable reg or a diode in the groung leg of a 7812 and use a suitable high current NPN power transistor for main regulator. This eliminates potential regulator mismatch issues. Only real concern is a large enough heat sink.
Earlier Max suggested regulating field current which works if ripple is kept low enough. You might talk to an auto electrics repair shop about a self excited alt and if you can break into the field circuit to control output this way thus eliminating a need for separate 12V battery at start up.
With any solution the prime criteria is voltage control with full load ripple and no load alternator output being very important. Note that many alternators will output quite high voltages at no load or with full field current. This could fail the attached regulator circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
Earlier Max suggested regulating field current which works if ripple is kept low enough. You might talk to an auto electrics repair shop about a self excited alt and if you can break into the field circuit to control output this way thus eliminating a need for separate 12V battery at start up.
The rectified ripple of a 3phase supply is only around 5%, the one I built was originally for a 250vdc 100amp generator.
With the LM311 design, the 12vdc output is kept constant.
Max.
 

djsfantasi

Joined Apr 11, 2010
7,689
very cheap idea is IC 7812 USE IN PARALLEL IN NUMBER OF AMPERES each IC serve 1.5 Amps and it must be mount on Good heat sink. at alternator out put link 10000mfd cap 25v .
Question, I’ve never used 78xx in parallel. Does one include separate capacitors on the input and output, or one larger cap on the input and output?
 

Ian0

Joined Aug 7, 2020
2,192
very cheap idea is IC 7812 USE IN PARALLEL IN NUMBER OF AMPERES each IC serve 1.5 Amps and it must be mount on Good heat sink. at alternator out put link 10000mfd cap 25v .
A 7812 needs 2V heardoom, if there is any ripple on the 14V then there may be ripple on the output.
Nothing wrong with parallelling regulators, but parallelling a few for each load four times, would perhaps be tempting fate rather less than parallelling them all.
 

Ian0

Joined Aug 7, 2020
2,192
A very obvious way to deal with any possible ripple would be to connect a lead-acid battery to the output of the alternator. An added advantage is that the system will keep going for a while after the petrol runs out.
 

prepka

Joined Oct 5, 2020
13
In my opinion analog regulation will not work here. A 7812 needs 2.4V higher on the input terminal to regulate at full load though it will be slightly less as load levels go down but not less than 1.53V at no load. The pass transistor idea is good but the same problem when adding a drone in the ground leg and also significantly worsens regulation over load range. You really need to.know what exactly is powered by the 12V and what the maximum input tolerance needs to be to work correctly. There are probably buck regulators on the board to power the microprocessors and their support chips of 5V or lower that will not be bothered from slightly higher input voltages. In a normal PC, the 12V powers the hard drive and CD/DVD and maybe an amplifier if it powers an amplifier for speakers. The power tolerance on these devices does not actually have to be exact and as long as maximums are not ever exceeded then all should be fine. I would suggest being a good large capacitor and a choke inductor band another large capacitor to filter any spikes from the source. Alternators are known to put out large spikes and the battery that is normally connected to them filters these out enough for the car computers they connect to. That is why you never disconnect the battery when the car is running. The switching regulator types on the newer cars can put out 100V or higher spikes when unloaded.
I would check out the circuit first before connecting it it your boards.
 
As an ASE Master Tech since 1978, The “Delco” 10-SI was used on everything in the 60’s. 6 cylinder engines had outputs of 20 amps. It use a voltage regulator the controls ground the the rotating coil to produce the 3 phase a/c that is rectified into voltage. It uses one wire from the key, but a 470 ohm resistor has to be used in series as full current with destroy that voltage regulator faster than you can say “Syne Wave”. The voltage out is two fold. One, a good battery at 100% of charge is 12.8 volts. The task of starting drops this voltage, the BAT wire to the alt’s output senses this a output voltage goes up. Inside the alt. the diode trio provide the regulator with voltage to operate at 400 hrz but a ceramic temp sensor at the back of the housing detect air temperature coming in as the front fan is centrifugal pulling air over the hot diodes first. It has no-chrome wire wrapped around it and if cool or cold, voltage goes up. Cold batteries are charged with “Dumb” chargers on high. The rest is system current. With a working alternator, the battery can be removed (Don’t try on 90’s and up / they control positive to the rotor) The Fix; Measure at room temp the ceramic resistor then heat with hot air, measure Min-Max. Use a good battery but insulate the terminal leads, run outside to potentiometer bolted to the alternators end frame without touching. Remember to run large gauge wire from end frame for negative as this is where negative is produced. I don’t know your setup but if you keep the driven speed constant set it, put gauge on it and dial in out voltage. You can find 20 amp stators, bearings, brushes and parts at www.alternatorman.com
Hope this helps as I rebuilt these for decades before boxed remanufactured stuff was used.
 
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