 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Solar : Small 48 V DC Generator.
| Author | Message | ||||
| Davo99 Guru  Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Fathers neighbor has his offgrid solar power system up and running finally. He is Back feeding a power circuit and was excited as all get out when I showed him yesterday if he put the fuses back in the whole house would power up. He was wiring the house internally with flat cable over the door arches and along the Skirting boards ( Face palm!!) He has no generator however and I was wondering how one of these 48 V DC motors would go if engine Driven? Has anyone used one as a small Battery charging Genny and if so,how much Power would one expect from one in this sort of Config? I see they are available in 1000W and 1600w. Would they do 50% output as a generator or more and would they run enough voltage for battery charging with out going too far over speed?  |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Dave, can you provide a link to any data or specifications ? Cheers, Tony. |
||||
| Old Seagull Man Regular Member  Joined: 21/12/2019 Location: AustraliaPosts: 55 |
https://www.ebay.com/itm/MY1020-1000W-48V-UNITE-DC-Electric-Brush-Motor-11T-for-Go-Kart-ATV-E-Bike-Scoote-/273363305367 Same type of motor. So info should e a good guide |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
O/k thanks for that, a Google search turned up some numbers: https://www.motiondynamics.com.au/unite-my1020-1000w-3000-rpm-48v-dc-motor.html  On the extreme right column there are some figures for speed versus load at 48.13 volts. No load (at 48.13v) 3,719 rpm at 1.86 amps which would be friction and windage losses. Absolutely flat out, 2,873 rpm at 33.45 amps. 1,218 watts out, watts in (33.45 amps x 48.13 volts) equals 1,610 watt. Drop in rpm under full load (3,719rpm minus 2,873rpm0 equals 846rpm. Internal power dissipation (1,610 watts minus 1,218watts) equals 392 watts. That is rather a lot for something that physical size. Now if run as a generator, with no load on the output, it would need to turn at 3,719 rpm to generate 48.13 volts, the same as when run as a motor. At full load it would need to be turned 846rpm faster to maintain the same 48.13 volts. So full power rpm (3,719rpm plus 846rpm) equals 4,565 rpm. The big problem though, is power loss and 392 watts of internal heat generation. You could not run full sustained power for any length of time on a bike, it would kill the battery. On the other hand, when used as a generator, continuous operation at some(?) useful power level would be expected, and that would depend on safe temperature rise. It does not appear to have a fan or fins or any real method of effective air cooling, so I would expect it to overheat very quickly when used as a continuously running generator, and I suspect its life might be quite short in that application, even if run at very diminished power. My gut feeling tells me this is going to be a bit of a disappointment as a generator, it would certainly produce the power, but only for a very brief bursts, before it quickly overheated and eventually dies. Cheers, Tony. |
||||
| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Thanks Tony And Andrew. Found these that have Fan cooling like a normal Induction Motor. Being these are DC and The magnets would be on the outside of the casing, Would the cooling actually do anything? https://www.ebay.com.au/itm/Differential-Speed-Motor-Electric-Tricycle-Motor-48V-60V-1500W-Electric-Motor/114203723648?hash=item1a97128780:g:seoAAOSw-Xtep9QS&frcectupt=true What would the input to a 48V Battery pack be with one of these? Are there any other Low cost, pre made alternators or motors that could be used? I'm thinking he may be better to do what I said all along and re configure the battery setup to 24V so he could use a car alternator. Less than Ideal and not exactly cheap either but for when he needs it...... He has a Chinese wind turbine which is less than useless where he has it but might be OK on an engine... although I think the output even when engine driven would still be pretty much useless. I think it's 400W rated but from what I have read, would be a lot less in practice. Not really worth worrying about most likely. Weather up here is predicted to be pretty ordinary to wet for the next week so Might be his first test/ wake up call. He has a lot of resource in Fire wood, Maybe I should suggest a steam engine and hook an alternator up to that? Ohhh, On 2nd thought, This would not be a man that would be a wise idea to put near steam. I could see his house and my fathers going Missing. |
||||
| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Better off using one of these dc welder , current controlled charger and just use any standard genny.. You may have to add 1 - 2 turns on the internal transformer to get maximum current... but very easy... I think it works !! |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
A lot of these light duty motors are not rated for continuous flat out use. Things like treadmill motors and bicycle motors can work well, but not for hours on end at full rated power. Now a dc motor can be run as a generator at a reduced voltage and speed, which may be more realistic for a reliable generator anyway. For instance, a 180 volt treadmill motor might say 4,200 rpm on the rating plate. If run at 48 volts that would be 48/180 x 4,200 = 1,120 rpm It would probably make a rather nice 48v dc charger if run up to about roughly 1,500 rpm under load, which is a very practical speed. The serious overheating problem still exists, but if external forced air cooling is used with something huge like a bilge blower, continuous full rated current, or even a tad more might be possible. I am running a single treadmill motor at about 3,000 rpm and getting 1Kw (100v & 10 amps) cooled with a 12v bilge blower.  As my battery is only 50Ah anyway, that is heaps on a cloudy day. No need to fully charge the battery, just enough to stop it from reaching minimum voltage is all you really need. Let the sun do the hard work. Always possible to couple up more than one treadmill generator to the same engine and use a single bilge blower feeding through some 100mm plastic pipe.... Cheers, Tony. |
||||
| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
The Treadmill motor is a great Suggestion. Never thought of that although I have heard of them before. I was wondering about an Unmodified F&P motor run through a 3 Phase Rectifier. I Imagine the thing would only need to be turned pretty slowly. Obviously best to re wire them but not something the Neighbor would be interested in and I'm not either. :0) Did one years ago, that was enough. Forgotten more than I remember about them now. Anything Higher power in DC never seems Cheap. Is there any sort of run of the Mill conversion with DC motors as Generators as to what one would get out of them in reverse operation? Out of interest, is the heat problem the same as when used as a motor or are there other things at play when reversing them? I have used the DC scooter type motors like in the first Pic for many years and they certainly do get warm especially at full tilt. I only use them on an Oil pump for about 5 Min or less at a time. Always amazed at the torque those things have. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Permanent magnet dc motor should work as a generator, they are completely reversible in function, and with similar efficiency either driving or being driven. The thing is, many (most ?) types of common permanent magnet dc motors are only rated for intermittent service. These can be extremely powerful for their size, but after only a few minutes at full load will very likely be smoking hot. Cheap and heavy duty, are not going to happen, unless you are lucky enough to pick up something fairly large and very old. The only thing I can really think of right now, might be an old (or a new Chinese) wind generator, but even that might need some extra cooling. In its original application its only going to be working really hard in a very high wind. Driven equally hard indoors, it may not be entirely happy without some help. In your travels, you might be lucky enough to score a storm damaged wind machine that still has a functional generator. Something that may not be economic to restore as a wind machine, might make the basis of a really super petrol or diesel powered battery charger. Edited 2020-06-18 17:54 by Warpspeed Cheers, Tony. |
||||
| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Golden motor in china Link have a huge range of perm mag DC motors; one of the scooter type may be ok. Mike |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I would not discount an F&P too quickly. The wind turbine guys usually have to rewire theirs because they have to match the blade operating rpm to the battery voltage to get any kind of workable efficiency. The other reason for rewiring an F&P is to rearrange the windings to provide a higher current at a lower voltage. If you are going to drive it with petrol/diesel, the F&P drive rpm can be very easily changed by pulley ratio. Much easier to do, and other issues such as cogging will not be relevant either. Now with petrol/diesel you can run the F&P faster (spin dry speed!) to achieve a higher ac voltage output, something the wind guys just cannot do. Suppose you run it fast enough to generate 230 volts ac three phase (at a lot higher than 50Hz). Then use three fairly ordinary off the shelf transformers to drop the ac voltage down to maybe 50v to 55v volts to drive your battery charging rectifier. That was just an example, no real need to drive it that fast. You can run it any speed and voltage you want within reason, then just use transformers that have a suitable primary to secondary turns ratio. Home brewing some transformers would not be that difficult. The much higher operating frequency means far fewer turns and a smaller core for the power. The F&P would also be a good choice because of its size and open frame construction, much better cooling potential than an almost totally enclosed dc motor. It would require three transformers, but at least you don't have to get in there and molest the F&P windings which would be an awful job. Edited 2020-06-20 11:37 by Warpspeed Cheers, Tony. |
||||
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Dave, if he has a std 240v generator you can plug in a welder and use that as a charger. Noneya had this one and it gave 1200 watts without modification. With modification it gave 3.5kw maxed out. I think he used Rossi ones as well, I don't know what they did out of the box. Even without mods, 1200 watts is still handy. Have a look here Cheers Caveman Mark Off grid eastern Melb |
||||
| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Very interesting with the welders and I like the F&P/ transformer Idea too. I was talking to the guy yesterday after surfing ebay and something dawned on me. Seems he has an inverter than can be set to charge the batteries from 240, pretty much just reverse the the thing as it were. He said he has the 4 Batteries set as 24V but that's not what I saw in the configuration or the voltage I measured. I don't know how he came to that conclusion but electrics are not his Forte although credit where credit is Due, he seems to have learned a lot and put some decent study into reading every word of his inverter manual. From what he said and I got the idea looking at what I think he bought, it should be possible to just get a regular generator, plug it in and set the thing to battery charge and it will do it that way. I spoke to him about having a backup and he said he had been thinking about that. I said you get a week of wet weather and you'll need one. Watching his house, only a few panels I saw get sun for even a couple of hours if that. So many 150Ft trees around there. My father has more panels on his shed with similar shadowing and he's lucky to make 2 Kw a day on a sunny day atm. Seems for him a regular genny may be all he needs. He could have the house connected and set the inverter to charge mode ( from what I understand) and it will bring the batteries back up. From what he said it can also be left connected to the mains and supply power at the same time like a Tesla battery I think. This one Might be a simple solution for the Neighbour. I'll bet he'll buy the cheapest, probably used, generator he can find if he does get one. He was asking me about the solar controller for heating his water. Must have had to refill the 9Kg BBQ gas bottle he uses on his camp shower and had a coronary he had to pay the $20 for the top up. I told him not going to do him any good in winter. I didn't realise how shaded his place is at this time of year. I suggested a gas hot water heater with the gas burner removed and put it on a stand and light a wood fire under it or use and oil burner I just set up. That way he could do it batch mode and only have to fire it every 2nd day or 3. I said if he got a bigger electric tank and circulated the water through that, Might last him a bit longer. Anyway, I have tried to give him the heads up so up to him what he does. I stressed he wants to keep the batteries as charged as Possible and draining them down will shorten their life severely. had I been going down that road, the FIRST thing I would have got myself was a generator but he does have a very perspective. This was an interesting learning question though. Seems there are a few ways of getting round the problem. My Father has a Big ass MIG welder I'm going to get which he no longer wants. I'm going to see if I can replace the failed wire speed control board with a simple PWM controller on the motor. If I can I'll probably fix the thing and keep or sell it but if not, it has a very heavy old transformer, bunch of Mosfets and some big caps in the thing. |
||||
 Print this page |
