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Forum Index : Electronics : 5KW Battery Charger
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
What to do with a spare 5KW toroidal core, perhaps use it to build a big battery charger for use with a 230 vac generator. The requirement is to allow bulk charge into the bank independently of the existing solar chargers. There must be voltage control and perhaps current control at the charge end point. With a 100 or so amps I don't really want to be actively managing the output, would prefer to control the 230 vac side. 30 years ago I built something like this using thyristors and phase control, feeding a transformer, yes it worked but not that well. Also worked on high power rectifier sets that used bridge rectifiers with 1/2 the bridge being dual thyristors for power control, sort of old tech, so don't want to go there. Today is different we have mosfets, so what I want to do is chop the 230 vac sine wave into high frequency PWM controlled square waves and feed that into the transformer primary. To prevent the back emf spikes, an active clamp shorts out the primary when the other mosfets are turned off, some dead time will be required. Rather than use a diode output rectifier, will use a synchronous rectifier to keep the losses down. Here is a concept schematic:   The waveform after chopping.I don't know if the HF choke is really required here, but cannot hurt. Normally the AC mains would be rectified and the high voltage DC switched into a ferrite core for isolation, resulting in a compact power unit, however whilst I do have some ferrite cores to play with, I don't have any big value 400 Vdc cap's on hand; with this big core sitting here, shame not to put it to some use. Comments please, is there an easier way of building a big arse battery charger... Cheers Mike |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Mike have you looked at these cheap Chinese Inverter welders? Such as this or this They are only using lightweight high-frequency components to step down the rectified AC input. As standard they don't put out enough volts to charge a 48V battery bank but adding just one more turn to the small toroid on the output side does the trick. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 513 |
Be carefull with some of the arc welders... they can feed ac direct from transformer.. will need at least a bridge rectifier on output... the mini inverter ones are usually already dc output.. I think it works !! |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
I have, cost a bit more to get to NZ; but would still have to add automatic charge control etc to make it work and at 100% duty cycle would require a couple, so no won't be using them. Cheers Mike |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
If you are running an Ozinverter, you can hook up a GTI to that and feed it with rectified gen output. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
I have not got around to it but plan to trace out the circuit of the Inverter welders with the idea of scaling up to a DIY 5KW size. Just did some searching and found a schematic but it is not real easy to read.2018-07-15_151042_EasyArc_zx7-200_igbt_inverter_welder.pdf There are only 10 types of people in the world: those who understand binary, and those who don't. |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1419 |
Madness, I recently bought a CIG Weldskill 180i stick welder. I found a service manual for it which includes block diagram of the circuit, thory of operation, a simplified circuit diagram and repair/debugging flowcharts. All of the above helps me to understand how it works. The specs of this unit say it makes 180A @ 27.2V DC down to 90A at 23.6V DC Open circuit voltage I measured at 75V DC google drive link to manual wronger than a phone book full of wrong phone numbers |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Thanks Poida, can't help thinking the CIG is not much different to the Chinese ones but with a proper manual. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Thanks Mad\Poida, I imagine all those low cost inverter type welders are pretty similar in design, basic rectify the mains, PWM H-Bridge to ferrite core transformer for isolation and controls for current etc. The CIG unit 2.1KW continuous would be the max to safely run from a 10A mains wall outlet. Would still require > two for 5KW, so for me, not really an option, unless get some from the dump. renewableMark, yes that would be an option,however GTI's are not available here in NZ, in fact virtually no 2nd hand solar stuff ever comes up for sale. Still I would like to charge my bank independently of any low frequency H-Bridge type of inverter running in the system. Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Did a search on AliExpress, the guts of those basic welders are available without a case; now this is something perhaps better to experiment with. IGBT Welder Control Card  |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
For about the same price here in Australia you can buy the whole welder on EBay as per the links above. They are quite light apart from the PCB there is not much else to them. The toroid on the right in the photo above needs one extra turn, the factory winding is Aluminium, it is not hard to replace with copper. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Mike your proposed topology does work. I used the front end of your topology (minus output synchronous rectifiers) to have a controlled AC current source by simply using a POT to manually dial in a fixed pwm from 0 - max. The AC output looked to have almost no distortion. It was for measuring earth resistivity @ 25A RMS for a whitegoods manufacturer. It was going to incorporate a feedback loop to regulate to a set current but the project was abandoned by the customer before we got that far. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Duplicate post - but I will add, that the choke between the switcher & toroidal was required. And I never hooked it to mains only ~ 20VAC but I am confident it would work ok on mains. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
I wish, those links they don't ship to NZ.....  |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Cool, thanks wiseguy, might order some IGBT's 600V 60A or similar rather than mosfets and have a play, probably use pulse transformer for gate drive in order to take the inputs below emitter potential for good switch off. Sync. output rectifier can have parallel mosfets (3 or 4) for efficiency. Now how many projects do have on the go..... its endless. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I would be very interested in what you guys come up with, I have several inverter welders like this professional grade CIG jobbies. they are outstanding welders, I can weld something at 100 amps that a yum cha welder cant at 180 amps but I cant get them to run as a power supply at all. I know the lincoln welders dont work, there is to much "welder assist" electronics that cant be switched off.  I'm confused, no wait... maybe I'm not... |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I will say I have not used a big charger to take a battery up to 100% for many years, in this day and age it is just not necessary. I just bulk charge with them and use solar or small chargers to finish topping it off. I'm confused, no wait... maybe I'm not... |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Man we have had days and days of cloudy dull weather this winter, need something to keep the batteries fully charged, cannot rely on solar here in NZ. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
That probably explains why there are so many Kiwis living around here, typical winters day = clear blue skies and temperature range of 10 - 25. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
yeah, I understand that but there are practical things that become blindingly obvious when you do try and run a big charger. if you go completely off grid, the power comes from a generator, most generators with a capacitor voltage regulator struggle to start a big charger. Inverter welders are even worse, my 140 amp CIG's have a recommended generator size of 12 kw. A 7 kw cap reg genset wont run them at 100 amps. So we buy the biggest single phase generator we can find and end up running it for hours trying to top up our lead acid cells at a trickle. Alternatively we can install a bank that doesn't need to be fully charged (lithium) at a cost of 25% more, use a 2kw inverter genset and smaller PFC chargers but we lose that large reserve capacity for that once or twice a year night time heavy load.....so we start the little generator. Nothing is perfect just some things are a better match to certain situations than others. big chargers are great for installing and testing battery banks so that the job can be completed in a short day. I'm confused, no wait... maybe I'm not... |
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