A bike generator for the winter...

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AccordGuy
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A bike generator for the winter...

Post by AccordGuy »

I'm toying with the idea of topping up my solar power in the winter with a bicycle generator.

We've got an out house that is only used as a store room at the moment but could be a gym cum generator room...

I was doing the rounds of the car boot sales again a couple of weeks ago and picked up a 105A car alternator. I also have a mountain bike that was dumped outside my garage door about a year ago by someone who couldn't be bothered to repair the flat rear tyre tube...

My dad has some welding kit and I fancy a challenge. I've never done much welding (apart from repairing a car seat frame once) so it will be an adventure. Or maybe I'll chicken out and just lash something together with wood.

I made the mistake of getting an alternator with a multi-plug and then had to Google for ages to figure out what the pins were for. If I'd got an old-skool alternator with just the battery lug and the lamp terminal it would have been easy... Happily the alternator just turned out to be an ordinary type (not a ECU controlled one - like some new ones) and it just has a lamp terminal, a battery sense terminal and a ECU information terminal (FR) that can be ignored.

I tried running it up by putting a drill in the pulley spline but the drill could only just reach the cut-in speed and then the alternator actually slowed the drill with the load and drew about 4A from the battery (rather than charging it). It was making enough power just to excite the field coil but not enough to make a surplus of power... Still, at least I know the regulator and diodes are ok on it. It had come out of a car so could have been dead.

I'm now trying to find someone who sells extra long 6-vee drive belts so I can get it round the 26" bike wheel (with the tyre removed) and the alternator pulley. Reading on the subject it seems this is the only way to get the 30:1 gearing needed to get enough RPMs to run the alternator above it's cut-in speed.

Some sites have suggested that a washing machine motor is better as a dynamo as they have permanent magnets but I'll plug on with the alternator for now and see how it works out.
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Post by Sharkey »

Most exercise generator setups use PM motors because they are cheap and plentiful, and don't need to produce much in the way of output. They also have less loss due to not using a portion of the generator power to excite the fields.

Humans make a pretty pathetic prime mover. I think you'll find that producing more than 30 - 40 watts is very tiring. A trained athlete who is really pumped up and kicking ass on the pedals can produce 120 - 200 watts (10 - 15 amps or so at 12 volts) for short periods. Your car alternator is way-overkill for the application, but give it a shot.

You will almost certainly need to insert a variable resistor (rheostat) in series with the field of the alt. You don't want 90% of your output to go directly back into the fields, and having a method of "tuning" the output will allow you to find the sweet spot for pedaling at a comfortable rate.

A bike-gen can provide much-needed exercise in the winter months, and I personally think that putting that effort to a useful purpose is important, but don't expect to get a lot of power out of the deal.

I've heard stories of families who have children making the TV watching rule that the kids have to pedal to keep the TV going. Sounds like a good way to make sure that they aren't vegeing out in front of the tube all day.
AccordGuy
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Post by AccordGuy »

Yeah... except I'll get the wife to pedal while I veg out in front of the TV :D

Another brainwave I had was to rig an auxiliary battery in the car. When at home in the garage, I could plug the aux battery into the house and run it through a laptop adapter I have that boosts the 12V to 16V and use that to charge the solar bank. Then when I have to go to one of my offices that's 2 hours drive away, I could charge the aux battery from the car, maybe with some kind of gubbins that would only charge it during "regenerative braking" so as not to waste gas on charging it.
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Post by Sharkey »

??? Your car has regen?

If it's a Prius, you have a fairly large reservior of electrons that you could tap off in the traction batteries. I don't know that the SLI battery is charged by regen on those, in fact, I'm pretty sure it's not, and you'd be charging up with petrol (evil!). Would take a high voltage inverter to tap the traction batts, but you could regen that back into shape if you could beat the ICE to the job by doing a lot of braking right after starting the engine.
AccordGuy
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Post by AccordGuy »

Hahaha.. No it doesn't have a regen (it's a regular car) but when decelerating on overrun (whether braking or not) the alternator is still turning over at high RPMs while the injectors have cut off the gas so if you put a load on the electrical system then it gets the electricity for "free" from the kinetic energy rather than loading the engine. Not as efficient as a proper regen but you could safely draw 50A during that time.

I can recycle some electronics that I originally used for the opposite purpose - to eek out a bit of extra engine power by having a throttle operated relay to disconnect the alternator loads when accelerating hard (>80% throttle open). At night the electrical system on a car can put a load of some 300-500W on an alternator... With my gadget, when I put my foot down, the lights literally used to go dim 8)

If I reverse the sense of the throttle position trigger and take a feed from the speedo sender, I can rig it to connect the aux battery to the alternator only when the throttle is closed and the car is moving (a decelerating overrun state). If I just used the TP signal I'd end up connecting the load when stationary and idling (not good).

Rather than purely rely on the alternator regulator (which has a sense on the regular car battery) I'd probably run a mains car battery charger from the 300W inverter I have permanently installed in the glove box. That way the aux battery can be charged independently from the vehicle battery and I could control the charge load better. I could also switch the inverter to the aux battery when at home in the garage to deliver mains power to the house / garage directly.

I've got a bank of five 7Ah SLA 12v batteries left over from the solar lighting kits I've been buying cheaply for the 12W panels in them. That would give me 35Ah of battery in a very low profile that I could easily hide under the front passenger seat with a link to the glove box. Alternatively, I could put a second battery in the engine bay... Some years ago I moved the original battery to the spare wheel bay in the trunk (to shift the 20kg weight to the rear axle for better balance - I used to race the car and it was nose heavy and understeering). So now I have an empty battery bay in the engine compartment that might take a 70Ah deep cycle battery...
AccordGuy
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Post by AccordGuy »

Cruising the local car boot sales again, I scored a perfect condition exercise bike for just 5 Pounds!!! 8)

This solves some problems and creates others... I couldn't find a drive belt big enough to go round a 26" mountain bike wheel for the alternator and it seemed a bit of a shame to shackle the bike to a stand when I'd gone to the trouble of fixing the bike up a couple of months back (it needed a new tyre tube).

The exercise bike on the other hand is purpose built to go nowhere and has a smaller chain driven flywheel at the front with a rim that is spookily the exact same size as the alternator drive belt.

I found an old bit of 25mm board in the garage and set about making a base board to bolt the bike and the alternator on to. With a quick trip to the hardware store tomorrow to get some kind of brackets for the alternator, I should be ready to wire it up and see if I can make some juice. The only worry is that the flywheel is much smaller than the bike wheel so I'm not sure I'll have enough gearing to make the cut-in RPMs of the alternator. If not, I'll have to ditch the alternator and have another look round for some permanent magnet motors instead.

Before I saw the guy about the exercise bike, I did see some broken electric kid carts being sold at the boot sale. I had a quick look and they were 24V 180W motors with a small tooth chain drive (not the same as the exercise bike that has regular bike chain teeth). If I can find one that has a flat belt drive I might give it a go but then I'll have to build a voltage regulator to charge the battery. The beauty of the alternator is that this is all built into it already. I'll just need to pedal really fast.
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Post by Sharkey »

I doubt that you will want or need any sort of regulator on your bike-gen. The purpose of a regulator is to prevent the batteries from being overcharged by the output of the charging source. Unless you are an exercise freak of some great endurance, overcharging your batteries is very unlikely, simply stop pedalling when the batteries begin to overcharge.

As I mentioned above, if you go with the automotive alternator, you should pitch out the built-in or external regulator anyway, replacing it with a variable resistor so that you can adjust the amount of field current to match the speed and effort you want to sustain on the pedals.

This is one application where the "blocking diode" is going to be necessary. If you use a PM motor as a generator, you'll have to have the diode to prevent the motor from, uh, motoring when you aren't pedalling faster than the batteries terminal voltage-vs-generator output. In the case of the alternator, the built-in diodes wil prevent backflow into the stator, but the field windings will still draw current through the resistor when you aren't pedalling. You will most likely have to put a momentary-action bypass switch across the diode to "flash" the fields when you first start pedalling, few alternators will self-excite without some battery voltage to get them started.

I'd recommend finding a small PM motor and leave the alternator under the bonnet.
AccordGuy
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Post by AccordGuy »

After trawling the hardware store for various shelving brackets and nuts and bolts, I managed to cobble together the base board with the bike and alternator fixed in line with a big eye ended bolt to pull on the other end of the alternator bracket for belt tension. Luckily, because the pulley and belt are grooved, it doesn't have to be super tight to avoid slipping and the bike flywheel is grippy enough and big enough to not slip either.

I ran some tests on a small battery and I can just make the cut-in speed and a bit more with the gearing of 14:1 the setup has. The alternator has a delay built into it's field controller so that if you are quick and give the pedal a quick start, you can get over the cut-in RPM speed before the controller tries to connect the rotor and it's much easier to pedal. If you are too slow to start or slow down too much when running, you suddenly hit a "load wall" where the pedalling gets suddenly really hard, the output to the battery collapses and the alternator draws up to 4A from the battery. At that point it's better to stop and have a rest and then kick start it again. I'll have to rig up a switch as the alternator draws about 0.3A when at rest.

I used a little 12v Christmas tree light bulb as the charge lamp / field initiator (as in the car circuit) and then ran a long (20m) 16 gauge cable out to the garage from my solar batteries in the house. This alternator has a battery sense terminal so I ran a thin bell wire back to the +ve terminal of the battery clips as well. This worked out quite well as then the alternator could sense the battery voltage directly and compensate for the long cables.

The good news is that I could pedal the thing and push a steady 4.5A into the battery pack (it was almost fully charged anyway from the PV array today - first sunny day this week!!!). The charge light goes out when the sense wire voltage is greater than the battery sense voltage.

The bad news is that I'm unfit :lol: I could only sustain the 22+mph that I need to be doing for 30-45 seconds at a time. The bike has a computer linked to a flywheel RPM sender. You programme the computer with a real bike wheel size (I put in the 26" mountain bike wheel diameter) and it then tells you the simulated speed and distance travelled. With the need to make about 4A for the field coils and making a surplus of 4.5A into the battery that means putting about 120W of pedal power (not counting losses) into the thing.

If nothing else, I'll get a good work-out...
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Post by Sharkey »

Good to see you got the mechanical fabrication accomplished. I really want to encourage you to try bypassing the alternator's regulator, I think you'll find much more satisfactory results without it. Replace the regulator with a rheostat and you'll be able to dial in whatever level of effort you wish, from no effort (with no resulting battery charge) to full-on hard exercise. I also believe that you'll make more effective use of your efforts not expending leg power keeping the alternator fields at full power when it's not needed. An adjustable field supply will allow you to loaf along for a good while at a leisurely pace, and sprint for some serious amperes when you want to work up a sweat.

Although I've always considered exercise for exercise's sake as being ~really~ lame (weight lifting, running/jogging, etc) I could possibly get into some mid-winter workout if I knew that my toil was going to a good cause. I was just looking about in the wrecking yard where my radio client's AM tower is located, and there is a big pile of cast-off consumer scrap, including multiple exercise bikes. Maybe I need to go dig some of them out of the heap and try them out to see which is most comfortable. I already have a 40 volt PM motor I could rig up for the generator, and lord knows I could stand to not gain back the 20 pounds I've managed to loose in the last couple of months.
Jones'n4chrome
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Post by Jones'n4chrome »

Super cool topic.
I like to see the new developments. I think Sharkey's idea for the rheostat is the way to go, but if not, maybe you can sell one of those gizmos to Jane Fonda, for her upcoming video "SWEAT TILL YOU PUKE"
just kidding, keep up the good work.
AccordGuy
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Post by AccordGuy »

Jones'n4chrome wrote: "SWEAT TILL YOU PUKE"
just kidding, keep up the good work.
Hahaha... I like it. Yeah, the next step will be to play about with taking the regulator off but the bolts and screws were really tight when I tried them. Plus, I wanted to find out if the thing works ok before I break it 8)

I saw these WindBlue generators on e-Bay that are modified Delco alternators for wind power. They rewind the stators and replace the rotor coil with a big neodymium doughnut magnet inside the claw pole piece.

They claim 12v charging can start from 150 RPM and make 15A at 2000 RPM. It's a bit expensive at $230+postage though.

I swim quite a lot. I started so that a) I could go snorkelling in the sea on holiday and not drown and b) I wanted to lose 18kg so that my knees wouldn't hurt when climbing hills / mountains in Scotland - oh and c) stand a chance of getting a girlfriend. I'm not great at swimming and usually do a 25m length and then rest and then another and so on for about 30 mins. I guess the problem is that it built up my arms and shoulders more than my legs and it only takes about a minute to do a length so that fits with me only being able to do a 30-45s blast on the bike... no stamina :roll: Given the UK prowess in the Olympic cycling this week - I feel it's my duty to be able to cycle for more than 60 seconds up what is the equivalent of only a modest slope (based on past cycling experience - I used to cycle everywhere as a kid and then it all went wrong when I bought a car).

Oh, yeah... I can now free dive to 4m in a coral reef without drowning, did manage to lose the weight and I got married :wink:
AccordGuy
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Post by AccordGuy »

Some pics of the bike generator...

Image Image

At last week's car boot sale there were some guys selling broken / incomplete left-over stock from a catalogue shop again and they were trying to off-load 3 exercise bikes for 1 Pound! You couldn't tell if any were complete as they were all in bits in boxes but likely you could build one complete one from the three sets.

They didn't have any more electric bikes or go-karts this time though so I'm still on the hunt for a chunky PM motor...

I read some stuff about stepper motors making good generators and that they will become more common as things like washing machines start to use them instead of regular motors. They are good for generating because they have strong magnets and multi-phase windings (for the steps). Apparently, the use of them in washing machines is so that the machine computer can drive them and know / control the exact speed of the motor.
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Dennis The Bus Dweller
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Post by Dennis The Bus Dweller »

This thing is great, Have you put a meter on it yet?
Peace along the way
Dennis the bus dweller N.Y.
AccordGuy
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Post by AccordGuy »

Thanks Dennis!

Yes, when I use the bike I connect a 10A multimeter to the connector so I can see if I'm making any juice. If you pedal too slowly it actually draws about 4A from the battery! Just sitting idle with the charge warning light on it draws 0.3A... not ideal.

Trawling the car boot sales again yesterday I bought a neat 12V PM motor. It was part of a model aeroplane kit and is used for starting small petrol engines. It caught my eye because it has a good pulley bolted on it with a vee belt and flat belt section. It also has a weird rubber bit on the end which apparently is for pressing the motor against the cone on a prop rotor (so you spin it up just by the friction).

It had an integral momentary switch but I took it apart and shorted it out by soldering the reeds in the switch together.

Running it up on the bike's flat belt (just by holding it there and turning the pedals by hand) was a bit disappointing. It can make loads of Amps (7 or 8 just in this way of operating) but only at a maximum of about 4V... no good for charging without some kind of inverter to get to 14V.

Image

So I put it away in my filing cabinet in the workshop (filed under "useful someday") and set about taking the alternator regulator apart to see if I could do something about the massive field current this thing draws.

The Germans have really done a good job on this one! It's a Bosch alternator and the rotor brushes and electronics are all encapsulated in a single plastic thing. I could disconnect the stator winding from the thing to stop it drawing from the stator but without a battery connection, it wouldn't work at all. The charge lamp current was just enough to energise the rotor a little bit but then the alternator could (like the starter motor) only put out 5A at 2-3V... no good.

I tried putting some resistance on the stator-rotor connection to the regulator to see if I could fool it into working with lower rotor current (as I don't need the thing fully energised) but that just confused the hell out of the regulator which then started to oscillate the rotor current on and off.

The transistor housing was just plastic spot welded on so I cut it off to see if I could get at the brush terminals directly (you can get to one of them via the +ve battery terminal lug on the regulator. But sadly the other brush had no visible contact in the electronics box. A weird thing was that the electronics inside was a couple of bare integrated circuits connected together with very fine wires and then encapsulated. For some reason, they used a non-solid encapsulation material though. I touched it with my fingers and it was soft and squidgy and I bent some of the connecting wires in it (luckily none broke or shorted out). At least this meant that I could poke a test meter probe through the "jelly" and test the chip's contact points but no luck... the brush connections were embedded somewhere else in plastic (probably under the moulded-in transistor.

So I put it all back together and it still works... Next I might try something more drastic like drilling out the back of the brush housing to see if I can get a screw to contact the brush spring and so bypass the controller but I've probably got a 50% chance of breaking the whole thing then...
AccordGuy
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Post by AccordGuy »

Not much progress lately... It's been heavy at work, having to drive 130 miles every day and working 12 hours at a time. But the project finished today so I played with my bike gen again.

I took Sharkey's advice and put a diode on the output of the alternator with a momentary switch across it so that I could "flash" the alternator over to start it up. With just a blocking diode there, the alternator never gets going but if you press the momentary button, the charge warning bulb comes on and you can pedal up to the cut-in speed. When the ammeter shows some output you can release the button and keep pedalling. If I slow down too much or when stopping, the reverse flow into the alternator (some 3-4A as it winds down) is now blocked as well as the 0.3A it used to take in "standby". So at least when I've run out of steam and am waiting to have another go, the battery doesn't drain any more. It also means that now when I get too slow, the alternator will just cut out and stay out, removing the heavy mechanical load that the motor-effect placed on my legs as I slowed down. Otherwise you are just burning loads of calories and draining the battery at the same time :(

I'm still on the lookout for a decent PM motor as a alternative though. Or maybe even make something using magnets glued on to the flywheel as a rotor and and a bunch of home-made coils mounted around the edge as a stator. A few bike gen / wind power web sites I've seen have detailed making PM alternators from bits of plywood and epoxy resin!
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