40 Amp constant DC power supply @ approx 12 Volt

Thread Starter


Joined May 23, 2018
I am a pensioner doing experimental electrolysis development. I do not have an electrical engineering background but have successfully built simple electronic circuits.
I have this far succeeded in powering an electrolysis cell with a 12 volt battery system, which in turn was "recharged" by standard 8 amp, 33 Volt PV panels through a 12/24V VITRON 30 Amp (max) MPPT charge controller. The eventual application will be rural so it makes no sense to me to use a controlled commercial 230 Volt AC power supply.
One of the basic problems encountered with electrolysis cells is varying resistance over the plates due to varying factors. It is important to prevent runaway current in the cell when heat lowers the resistance of the electrolyte.
I have inquired locally whether "standard DC/DC constant 40 Amp controllers" for a 12 Volt or 24 Volt DC battery power supply are commercially available but without any success.
Is such a power supply a pipe dream or virtually impossible to be build by an amateur? Is a circuit diagram for something like this available?
Kind regards.


Joined Feb 24, 2006
Depending on the capacity of the battery (measured in Ampere-hours), a 40 Ampere load is going to draw down the batteries in a hurry. The batteries are going to need recharging from the mains. So no mains means you need an inexhaustible supply of batteries. I imagine you will need a truck to transport the batteries to the nearest source of AC power for recharging. On the other hand you might be able to use a wind turbine to generate the needed power, or some combination of solar, wind, and water.

Thread Starter


Joined May 23, 2018
Thank you Papabravo, The PV solar panels will be supplied according to the eventual weather expectations. For my development I have excess capacity in PV solar energy supply, parallel charge controller capacity to recharge batteries and a bank of 4 x 12 Volt 105 Amp-hours batteries. My solar capacity at this stage is roughly 2 Kw (2,4 Kw peak). The process is being designed to use only solar and wind. At this stage however I need to control runaway current. Perhaps the "constant" current requirement has been misleading. Kind regards.


Joined Aug 1, 2013
Are you asking about a constant current regulator that can be set to 40 A? If yes, what is the peak DC input voltage, and what is the lowest acceptable output voltage when the regulator is passing 40 A?

Note - a constant current regulator works by turning down its output voltage until the load draws only the designated current. So even if the input voltage from the batteries is a rock steady 13 V, the output voltage will decrease as the impedance of the electrolysis cells decrease. So if the cell impedance is 0.15 ohm and the regulator is set to 40 A, the voltage at the regulator output will be 6 V (Ohm's Law). This means that there will be 7 V across the regulator at 40 A, for a heat dissipation of 280 W. You'll need some fans.


Thread Starter


Joined May 23, 2018
Much appreciated Analogkid,
The peak DC input voltage I presume is either the voltage of the Vitron MPPT charge controller; 14,4 Volt or the charged voltage of a full battery bank appr. 13.7 Volt. The "internal resistance" of the electrolyte requires (when the process start} is roughly between 1.9 volt and 2.05 volt to allow current to flow freely and to produce adequate reaction. The second part of you question is unknown at this stage. I have this far protected the system by means of a 30 amp slow blow fuse. This fuse had to be replaced once already. I would like the system to run unattended so turning down the voltage is not desirable. Heat dissipation with 30 amps posed no problem for the present setup but will be attended to once I up the system to 40 Amps.


Joined Mar 30, 2018
I have a circuit in mind that might do what you want – but 4 or 5 of these wired in parallel might do what you want, giving considerable control over the output voltage/current and being far more efficient than linear regulation of the voltage/current.

The listing states that ‘two groups of current can work simultaneously without conflict’ my guess is that this is Chinglish for it being possible to wire two in parallel to give an increased current output – whether 5 could be wired in parallel to give a 40A supply is not clear. But in any event, you could include a diode at the output of each so that there was no danger of one unit feeding another.


Top tip if buying multiple items like this on ebay from China; order in lots of total value less than £18 to avoid paying import duty/tax (in the UK).
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