Lowering amps for charging system.

[graeme1198]

Hi all,

Wasn’t sure where to get some information, so I thought I’d ask the question here! FYI I have no electrical quals, I build custom motorcycles as a side hobby and have built a fair few looms over the years, all be it simple platforms.

Im in need of a little advise if something is theoretically possible and how the best way to go about it would be.

I’ve got a custom motorcycle which has a charging system output of about 17amp max chat. I’ve got a battery to work with that max charge
Rate is 4amps. (Lithium) this is all to do with space constraints it being so small.

Any way to step down that amperage? Adding resistance? Massive drop from 17-4 I know….

Any advise would be appreciated!

Cheers

 

[plugsandsparks]

Not fully understanding your terminology used but will give you some principles. Simple vehicle battery chargers using either a dynamo or alternator or magneto will generate a voltage , say for a 12V system, this will produce a voltage of between 12 and 14 V depending on the speed of the engine and load from electrical system including battery charging. The battery charge rate is mostly a function of the state of the battery since the battery voltage rises, as it approaches fully charged, naturally reducing the current. If you are fitting a lithium battery (i guess similar to what i have done on my car) i would check to ensure the battery is designed for this purpose. For example my car's limit for charge voltage is 13.7 volts, however the lithium battery fully charged voltage is 14.4 ( i think), this means that the battery will charge aggressively when very low and will naturally peter out to 0 amps at 13.7 volts (below the max of the battery) hence no risk of over charging.
If you post some details of the battery you have in mind and the type of engine electrical generator, i.e. alternator or magneto along with its operating voltage i may be able to work out what needs to be done (if anything)

 

[graeme1198]

Not fully understanding your terminology used but will give you some principles. Simple vehicle battery chargers using either a dynamo or alternator or magneto will generate a voltage , say for a 12V system, this will produce a voltage of between 12 and 14 V depending on the speed of the engine and load from electrical system including battery charging. The battery charge rate is mostly a function of the state of the battery since the battery voltage rises, as it approaches fully charged, naturally reducing the current. If you are fitting a lithium battery (i guess similar to what i have done on my car) i would check to ensure the battery is designed for this purpose. For example my car's limit for charge voltage is 13.7 volts, however the lithium battery fully charged voltage is 14.4 ( i think), this means that the battery will charge aggressively when very low and will naturally peter out to 0 amps at 13.7 volts (below the max of the battery) hence no risk of over charging.
If you post some details of the battery you have in mind and the type of engine electrical generator, i.e. alternator or magneto along with its operating voltage i may be able to work out what needs to be done (if anything)

Hi,

Thanks thanks for your reply sorry if my terminologies a bit mad.

The bike is a kick start only platform, so it doesn’t require much of a battery to operate everything. The small battery is appealing as it’s able to be hidden very easily.

I have an alternator system which manufacturer states produces 17A at 1000 rpm. This is a gear driven alternator. States in the instructions that at 1500 rpm’s. It should read 12 volts. At 2000 rpm’s 15 volts, and at 4000 rpm’s 26 volts. Comes with a regulator/rectifier.

Using an anti gravity lithium battery 401 (Antigravity Battery AG401 - https://www.antigravitybatteries-uk.co.uk/small-case-type-batteries/antigravity-battery-ag401.html)

I was concerned that the amperage was to high as on the battery itself or says max charge rate 4A….

Appreciate your help!

 

[plugsandsparks]

It looks like the Anti-Gravity battery is similar to mine, although smaller. Mine also has some in-built protection which made it MSA approved for Motorsport. The link is very specific about using a modern alternator with regulator/rectifier as you have mentioned. Its the voltage regulator that is vital here along with a full rectifier. This will ensure the voltage does not get too high. I can see where they have a note saying only use an approved charger, i think they mean when charging at home, rather than when the bike is re-charging the battery so i can see where you have concerns.
my advice is to contact Anti-gravity, confirm the battery will work OK with an alternator /voltage regulator as you have indicated and buy the correct charger from them for home charging. Thats basically how i tackled it.
You may need the details of the regulator / rectifier though, as the details you have provided about the alternator are voltages before the regulator ( i hope, lol)