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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 |
Hopefully this big charger will have a variable set charge rate by setting the default PWM control to whatever rate is required up to 5KW, with soft start on initial switch on; so I can use it on an el-cheapo Bunnings generator if required; that's the theory anyway. We will be using it on a bank of Lead-Carbon batteries, they behave similar to Lifepo4 in that they don't require full top up and work well with partial charges, can be discharged to near 0% capacity approx 1000x and seem to work identically to lithium in most respects but for the volume and weight. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Great stuff! soft start and dial up charge rate is a must. It probably wont work without it. I'm confused, no wait... maybe I'm not... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I wonder about PWM switching in the primary, where both source and load are going to be rather inductive. There might be some really enormous mosfet killing voltage spikes generated, and not much you can easily do to get around that. I think I would just couple up the toroid to clean 50Hz ac, build a conventional dc rectifier with a choke input filter, and follow that with a buck regulator that used a N channel mosfet switching in the negative side. The current will be a lot higher of course, but the whole thing becomes a lot simpler and more straightforward. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Oh, anyone thinking about using phase controlled SCRs for a monster phase controlled battery charger running off a petrol/diesel engine. Forget about it, its highly unstable. The problem is, that the SCR firing angle is usually generated electronically by some controlled delay after the previous zero crossing. This works wonderfully well connected to the grid, but... With a small generator, or even a very large one, the rpm will change with the electrical load. Now you need to think about this. If the increased applied load causes the rpm to fall, the frequency goes lower. The ac cycles get longer, and that causes the "apparent" firing angle to become earlier, even if the controller phase delay in milliseconds remains exactly the same. Earlier firing increasing the load even more, which lowers the frequency further. At some point both the engine governor and the SCR phase control feedback system BOTH try to reduce the rapidly climbing load together. Guess what happens next. Yup, the rpm rises and the load rapidly comes off as it does. The whole thing will surge uncontrollably. I have seen this effect many times, and it can be rather alarming both electrically and mechanically. I have also seen some pretty smart people (that should have known better) try to fix this. The diesel gurus with a bunch of different governor springs, and the electronics types with a box of assorted resistors and capacitors and time constants for the feedback control system. It cannot be fixed, its basically a very bad idea, so take heed. PWM will work fine, because the duty cycle is fixed and changes in supply frequency will not have the same effect as with phase control. Don't wish to sound like a wet blanket, a pessimist, or the "voice of doom". But some ideas have already been tried and found not to work. Just trying to save someone a whole lot of grief. Cheers, Tony. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
So is there any issues with using these inverter welders as chargers off of a generator. They have a rectifier and capacitor bank on the AC input side. I have been told any of the capacitor regulated type generators are a disaster with any electronics due to the third harmonic caused by the winding to generate the field. I have a small inverter type generator and the others are proper brushless Stamford type machines. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Don't really know Mad, but small generators are very different to the grid, and some loads either may have problems themselves, or may cause problems for the generator. Cheers, Tony. |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I can't bloody find it, but I remember Oz saying something about using BIG caps across the gen output and you could still run a small gen on a bigger load and it didn't stall the gen. Wish I could find it. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The problem with all this is that in the old days both generators and welders were fairly simple devices, often without any electronics in them at all. These days many things now have switching power supplies that may have some very unfortunate characteristics that makes connecting some loads to some power sources a fairly risky business. BIG caps across the output of an ac machine may help in some circumstances, or it may cause instant death to the generator, especially if its an inverter generator for instance. I would be very hesitant to recommend anything unless the exact identical setup has been proven to work and be long term reliable. Cheers, Tony. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You can use a capacitor in series for resistive loads like hot water elements and for AC into a rectifier to supply DC to a grid tie inverter to reduce the power. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Ahhh, series was it? That's why I wanted to find that post, now you've answered it. Cheers. Cheers Caveman Mark Off grid eastern Melb |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1026 |
Have been running an old Telecom battery charger for years off the generator, as yet have not had any substantial issues. Most often when we use it, we run at full current 55A up to 53.3v before it drops back. usually only run this setup for about half an hour, thats enough to survive overnight (keep the lithium batteries happy) till sunny the next day The generator is my avitar ST2 12HP. I might have trouble if I ran 2 of them on the same battery bank, currently only 320Ah many years old? I'm well interested in any new way to charge batteries as these charges are getting old, I keep getting told.  The charger has 2 massive chokes, and a capacitor bank that runs parallel on a circuit breaker? I think? Cheers Aaron Off The Grid |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
SolarMike, I know this is another option that is not using your torroid, but this is on my list of stuff to make here I got a couple of stators & hubs from machines left in the street, just need the motor and pulleys and time to do it. Looks like a simple solution. Like one suggestion, if it loads up too much simply back the magnet rotor off a bit with spacers. Cheers Caveman Mark Off grid eastern Melb |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Well yes it would work, back in the day 35 years ago when I had a full machine shop to play with, lath's, milling machines, welding bay, power cutoff metal saws, 40 Ton hydraulic press, 4 foot guillotine, folding brake, yeah could have built something like that, unfortunately I no longer work for that employer, so options are more limited. There is a place here in NZ that sells kits using those old smart drive units to make your own wind turbines etc. I was rather hoping we would not have to use an external backup generator, just wack up another 25 PV panels on posts in the paddock, but with the crappy weather at the moment, even that wouldn't be enough. Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
You could well be right there Warp, I was hoping the active clamp would direct those transients back into the core\load. I didn't really want to do switching in the output due to the high currents, big chokes and lots of parallel devices. I think a simple variable pot driving a pwm generator fed to some devices has to be built as a test, if it blows up not too much lost. Mike |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Is there no possibility of wind or hydro where you are Mike? The little inverter welders are a quick and easy way to get a 25-30A charge going, just takes about an hour to do the rewind. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The Mickey Mouse way to build a big mutha battery charger, is to use a car alternator hooked up to your petrol or diesel engine directly, probably through two stages of pulley drive to gain sufficient alternator rpm. These vehicle alternators start charging at about 2,000 alternator rpm for a 12 volt system. What many people do not be realize, is that at 4,000 rpm they would start to charge a 24v battery, and at 8,000 rpm a 48v battery. Only the voltage regulator stops this from happening. It just needs a simple home brew voltage regulator that feeds no more than 12v to the field winding under any circumstances. But the alternator and its diodes will work fine at 48v or 60v dc. Now 8,000+ continuous alternator rpm sounds like a lot, but it isn't. On most car engines the alternator pulley ratio is about 3:1 or 4:1 the alternator light comes on below maybe 700 to 500 engine rpm (about 2,000 alternator rpm). So going up through the gears to 6,000 engine rpm, that alternator might see 24,000rpm on a four cylinder engine. And it will do that for the life of the car without any problems. So running an alternator at 10,000+ rpm continuously is not a big deal. And you can still get the full rated dc output current, but at four times as much voltage. That is a LOT of dc power, and all from a $10 junk yard alternator. Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Hydro is out, small creek doesn't have enough water, even though it flows all year. Wind might be an option, this install is for a charity, so funding is always an issue to get things like wind turbines, I will get a wind map of the area, I guess someone has these, see if the location is suitable. Cheers Mike |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
That is a good point, an old 4 stroke lawn mower engine coupled to an alternator from the dump, does sound like a viable option, I will pass that idea on, let someone else possibly have a go at that, I can build the electronics if it works out. Cheers Mike |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
An old horizontal shaft Briggs, a junk alternator, and an old air compressor all bolted together so you can swap the drive belt between the two might be a useful gadget. Cheers, Tony. |
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Chopperp Guru Joined: 03/01/2018 Location: AustraliaPosts: 1057 |
I've often wondered if there was a reduced current limit in doing this. Now I know there isn't. I've been using a 12V alternator to charge a set of 36V (42V) batteries for many a long year using a home brew regulator feeding the field from a 12V supply. Obviously you need the revs to get a decent output as mentioned. Thanks for the info ChopperP |
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