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toning down a 10A 'smart' charger for flat battery?

Discussion in 'Technical and Troubleshooting Torque' started by chokpa, Jul 3, 2010.

  1. Hi All,

    Just got a VTR250 which hasn't been ridden for at least a month. Tried charging it a few times today and i wasnt having any of it. At first it was semi successful, then it just got less and less willing. User error i'm guessing.

    Tried push starting but in the end the battery is flat as a pancake.

    I managed to borrow a 10A "Smart Charger" from a friend. Basically for dead batteries it'll initially charge at 10A and then gradually give it less juice.

    Is there any way I can just get it to charge at lower amperage from the get go?

    I imagine charging it at 10A will just fry the thing.

  2. Do you have a multimetre?? $12 from Dick Smith/Jaycar/SuperCheap

    You should be fine, just charge it for a few hours

    Or invest in a proper floating/trickle charger ~$50
  3. cool - so the initial 10A hit will be alright?

    can a multi restrict amps? Sorry, pretty crappy with electrics.
  4. cheers toe.

    I might just wait til I see the mechanic and get him to charge it. I gotta go get a pink slip anyway.

  5. Charger will not hurt the battery, it'll step down quickly.
    I've been using a standard car charger for years.

    One thing, don't forget to check the water levels after charging, it's normal for some to evaporate.
  6. apparently a trickle is $20 at supercheap so I might just get one instead of risking breaking it.
  7. To 'tone down' the initial charge rate, just put a headlight bulb in series with the battery. I keep an old bulb with a blown low beam just for that purpose, or just pull the one out of your bike while you're charging.
  8. Actually putting a globe in series will only change the voltage across the battery if the charger is a true 10 amp. You need to find the resistance of the battery preferably under charge and then place a globe or resistor in parallel with the battery to ensure the current has somewhere to go. The current through the battery will be proportional to relative resistance or globe. You could try another battery in parallel, but you may end up wrecking the charger.
  9. yeah im not keen on the whole stick another battery in parallel thing.

    How about a 6A charger? I saw one floating around 2nd hand and it costs $20 less than the projecta I saw which is $50 delivered.
  10. One of the reasons chargers start out charging at a higher amperage is to 'breakdown' some of the memory, etc of the battery.

    When you start a bike, car, boat or whatever it is plausible and often the case that the charge coming out of the battery is (much) greater that 10 amps, depending on the circuits (read resistance) involved and the type of starter on your machine, so an initial charge on those batteries greater than 10 amps is probably ok also. The worst case scenario is you battery is completely stuffed and you short the charger.

    To be completely sure - and I don't know much about bikes yet - you need to do some research on your battery and typical current draws when you start your bike, and have some idea that the battery is ok and can take a charge.

    My initial guess is that if it is a 10 amp smart charger you should be ok. A good charger these days is able to measure the current in, the voltage across the battery, and hence the resistance of the battery, all of which help tell it the battery condition, and capability of the battery to hold a charge.

    Perhaps it would be wise to take the battery down to a battery world or the like to see what they say about the condition before you try and charge it. They are usually pretty good and should give you some good advice. That'd be what I'd do and I have a degree in electrical engineering...

    Hope this helps.

  11. I am not an electrical engineer, however I can say that watts divided by volts equals amps.

    And that your headlight, starter motor, horn, ignition, tail light, and flashers will draw far far more than 10 amps; not that they would all be going at once. None the less, the starter motor alone is likely to draw far more than 10 amps by itself.

    Taking that lot into account, if the battery can discharge at far greater than 10 amps, it can charge at 10 amps, especialy for a short amount of time.

    If you doubt this, put the battery on the charger and moniter the temperature of the battery. ie Put your hands on it just to make sure it is not more than warm to touch. If it starts to get hot stop charging it.

    WARNING DISCONECT THE EARTH (NEGATIVE)LEAD. even better remove the battery from the bike.

    ALSO the electrolyte is a sulphuric acid solution avoid contact with it.

    10 amp 12 volt charger is good!
  12. I'm assuming your bike is 12 and not 6 volt :eek:
  13. Also...another WARNING Do not ever check the fluid level in the battery using a naked flame as a light source.

    Hydrogen is produced by lead acid batteries and an exploding lead acid battery will spoil your day very much indeed.
  14. haha what kind of idiot would hold a naked flame to check a battery.

    Anyway thanks Bugs. I ended up getting a Projecta just to be sure. My bike is yet to get a pink slip so I don't need it to crap its battery out and need that replaced too. Played it safe and got a trickle charger from Projecta.

    Turned out a friend of mine needed it too, so we've gotten some value out of it.

    Thanks for your help. Stored it in my brain for later ;-)
  15. The answer to your question is "The kind of idiot that does not know any better"

    It has happened to many before. The results are horrendous.

    Better for me to make the warning, than have some idiot... (and there are plenty of those) blame me for having a battery explode in their face.
  16. By the way, when your service manual arrives check out the output spec on the alternator... that's the thingy installed on the bike that charges the battery.

    My estimate is somewhere between 18 amps and 30 amps.
    which makes the ten amp charger; which you are worried will damage your battery look... kinda idiotic.
  17. My thoughts exactly. Vehicle batteries are astoundingly tolerant of massive charging currents.
  18. Pretty much agree with what is said above in terms of what a good battery should be capable of taking in terms of amps into the battery. As I alluded to, most vehicle batteries need to have a fairly large current draw available to turn over starter motors in vehicles. Compared to other loads on the battery, it is the major current draw a battery has to deal with, and is more so when it is the only battery available as is the case on a bike.

    I say this because you can buy vehicle batteries that are more suited to running things like fridges, inverters, etc that involve a lower current over a larger period over time - versus batteries that deliver large currents over a short time that turn things like starter motors. Both can have the same ratings on terms of amp-hours, but because of the way they are built are not suitable for the same functions.

    Having said that, if your battery is no good to start with because, for example, cells may have broken down inside it (for whatever reason), no battery charger is going to be able to charge it no matter how good the charger is. Over a period of time batteries do, and will, deteriorate, and you will have to replace them. You can measure the condition of a battery a number of ways, via load testing, hydrometer readings, or a combination of both. The thing is, to do so, you need equipment that you probably don't need to buy. The simplest thing to do is to go to a battery shop and get them to measure the condition for you, which most will happily do.

    If your battery is no good, there is a chance that you can do damage to the electronic circuits on you bike as well as the charger. Worst case scenario is if a couple of cells are broken, and the stress of use breaks down a few more causing a short circuit either on your bike or across the charger. It can be a fire hazard. So get the battery checked to make sure it is ok. It should be free to do so. Incidentally, have a read of this: http://www.batterystuff.com/tutorial_battery.html#5

    It may answer a few of your questions. Google is your friend.
  19. Incidentally, be careful about using trickle chargers as it is possible to 'overcharge' a battery. Many people use a timer as well to ensure thus doesn't happen.