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More electricity...

Discussion in 'General Survival and Preparedness' started by Pax Mentis, Sep 3, 2013.

  1. Pax Mentis

    Pax Mentis Philosopher King Site Supporter

    Hand Crank Generators

    I haven't seen mention of these on the board and just purchased one so thought I would share the link.

    We have gas generator, small solar array, small windmill and a couple of small charging alternators with a homemade setup to use the flow of the river (we have both a "narrows" and 2 decent rapids on the property) or with bicycle frames, but this struck me as a handy backup for keeping things like handheld radios and rechargeable "letter" (aa/aaa, c, d) batteries charged.

    Once I get it and use it a bit I will try to drop back and post a review.
  2. Motomom34

    Motomom34 Moderator Moderator Site Supporter++

    I am poor so even though a hand crank generator generator would be awesome it just isn't in the budget. I am very interested in the small solar array and the windmill that you mentioned. I have been wanting to experiment with solar to learn the how to's and to judge for myself how effective it would be at our home.

    Did you make your windmill?
  3. cdnboy66

    cdnboy66 Monkey++

    be a great setup if you could attach a drive from a windmill too.
    kellory likes this.
  4. Motomom34

    Motomom34 Moderator Moderator Site Supporter++

    So I started googling after seeing Pax's post and there are instructions on how to build your own hand crank generator. I would try building a mini one but I think it is do-able. I know I could get a used alternator at the junk yard. I am going to start accumulating stuff and we should be able to figure it out. Has anyone here ever build their own?
  5. melbo

    melbo Hunter Gatherer Administrator Founding Member

    I have one that I purchased maybe 10 years ago. I remember testing it out but don't remember the outcome. I think the problem with a lot of these is that they are of pretty cheap quality. Need to lay my hands on the circa 1950s dynamo that used to sit on my fathers work bench.

    Please share some results with us!
  6. natshare

    natshare Monkey+

    Lurker and Icefoot like this.
  7. Airtime

    Airtime Monkey+++ Site Supporter

    When following the link to the website I was at first rather intrigued. Then I saw numbers like 400 watts and 1600 watts and claims of running all kinds of appliances etc. Then the specs on the batteries were in cold cranking amps and not in amp-hours. Wait a minute, this isn't ringing quite right and the skeptical engineer in me kicked in so I had to run through some numbers to see if this made sense.

    So, let's establish some facts first. How much power can a human generate and for how long? I remember this being researched a bunch for the Gossamer Condor and the Gossamer Albatross developed to win the Kremer prizes years ago for the first human powered aircraft to have sustained controlled flight and then to cross the English Channel. Digging into human power found a nice chart here:
    Program: hpv (updated 6/22/11)

    I suspect most of us would be "healthy humans" capable of producing about 0.2 HP for 3 hours before being exhausted.

    From the picture of these systems, they use a V-belt drive from a very large diameter sheave to a very small sheave of the generator/alternator to get the RPMs up. Belt drives have some efficiency loss as the chart on page 7 of this presentation shows from this website:

    The chart shows the smaller the sheave (pulley) the lower the efficiency. On this generator one is large one is small so let's assume say 94% efficiency.

    0.2 hp x .94 = .188 HP delivered to the generator.

    To look at things in watts, 1 HP = 746 watts

    So we have about 140 watts available at the generator shaft. From here we see that permanent magnet generators range from 75-95% efficient with the average being about 85%.

    So the actual power that a healthy person can deliver to actually charge a battery is at best about 120 watts for three hours and thenn you will be exhausted. Oh wait, that is what a healthy person can do with pedals. Try that with a hand crank and as the generator manufacturer acknowledged it will be about half. So a person turning the crank hard by hand can generate maybe 60 watts for about 3 hours or about 30 watts for 8 hours.

    In a SHTF situation, this might be just fine if you are holed up in a bombshelter for 2 months and need the exercise, but I think if one is not buried under ground, there may be better ways to spend multiple hours a day. And a good solar panel for mounting on one's roof is 250-300 bucks for a 200-240 watt panel that can work as long as the sun shines.

    Bottom line, interesting product but it's not on my list of things to buy. Just my opinion.


    Edit addendum: It should also be noted that some energy will be lost in charging a battery and then in the inverter that converts 12 into 120 volts AC.

    As noted in the link below, for a typical 6 cell lead acid battery, the charging efficiency for a modern charger is about 75%. That takes us from 120 watts of pedal power down to 90 watts.
    Section 3. Battery Charging

    The efficiency of a good quality Xantrex pure sine wave inverter is 90%. Now we actually are at 81 watts for 3 hours yielding a total energy of a bit less than 0.25 kilowatt-hours of useable energy yielded for three hours of pedaling and about half that for hand cranking. Now look at their test data in context.

    The website had "test data." One of the impressive claims was they ran a 600 watt hot plate for half an hour. That would be about 300 watt-hours or 0.3 kilowatt-hours of energy. So to run the hot plate for half an hour would require about 3.7 hours of pedaling or about 7 1/2 hours of hand cranking to charge/recharge the battery. YMMV....
    Last edited: Sep 4, 2013
    Motomom34, kellory and melbo like this.
  8. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    I've seen this guy before, but this was more in-depth. thank you for posting it. I hear you can use a cordless drill for the generator as well. Harbor freight has them for about $20.
    Motomom34 likes this.
  9. melbo

    melbo Hunter Gatherer Administrator Founding Member

    Nice info and thanks for putting it in perspective!
  10. Seawolf1090

    Seawolf1090 Adventure Riding Monkey Founding Member

    Handcrank Generators are designed to provide temporary power to small devices, like radios, for the Army or other groups in remote environments with a lack of fuel. I don't see them really useful to preppers unless you just want to run your Ham radio to talk to someone. Trying to charge batteries simply isn't feasible.
  11. Pax Mentis

    Pax Mentis Philosopher King Site Supporter

    Got it about 10 days ago and when it is set up with my son's mt. bike, I must (somewhat) respectfully disagree with Seawolf and Airtime.

    Not trying to sell one to anyone, but it is very well built, as well as much more efficient than the various setups using truck alternators and various power sources we have. I am very happy with the purchase.

    YMMV, of course.
  12. Silversnake

    Silversnake Silverback

    From a pathophysiology standpoint, a repetive motion like operating a hand crank for 3 hours straight is a fast track to an overuse syndrome, tennis elbow, golfers elbow, subacromial bursitis, deQuervain's tenosyovitis, bicipital tendonitis or other soft tissue inflammation of an upper extremity. You probably won't be able to do more than 2 iterations of this with a day in between before the average person has something inflamed to the point you can't do it again. Using a bicycle set up with pedals is a better bet.
  13. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    Or better yet, let the windmill spin it.
  14. Airtime

    Airtime Monkey+++ Site Supporter

    Just curious: regarding the energy assessment I wrote, with what exactly do you disagree?
    The sources of the data used for the base assumptions? Did I make a mistake in the calculations or the engineering analysis (wouldn't be the first time)? Something else?

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