Alternator Information

This is a brief overview of currently-known alternator information for the Ninja 250. This information is only likely to be helpful to advanced mechanics.

Tiny alternator glossary:

Stator: The part of the alternator which is affixed to the bike, inside the left hand engine cover. This part may be replaced with some work.

Rotor: The part of the alternator which spins, affixed to the crankshaft. No aftermarket replacements available.

A stock alternator stator was sent to Electrosport for testing. They sent back the following results:

	Core Thickness	Output (A) @1000rpm	1200rpm	1400rpm	1600rpm	2500rpm	3600rpm	6000rpm	Power(W)@13Vdc
EX250 OEM Rotor (stock)	13mm	6	8	10	11	13	14	15	180W
ESG110 Rotor	15mm	6	10	12	14	17	18	19	230W
ESG636 Rotor	19mm	1	6	10	14	20	23	25	300W

Note that all stators make nearly their full power by 1400 RPM, which is approximately idle speed.

No information has been collected on how much power the bike requires while running. This information is necessary to accurately determine the actual power overhead available. Common wisdom is that there's about 60W overhead available for accessories (lights, heated clothing, etc.) with a stock stator, which would imply that the bike needs about 120W to run. IanJ is planning on gathering this information, but it's not currently a priority.

Electrosport reports that the ESG110 stator can be installed without modifications to the engine case, although it does not come with the correct connector, and will require cutting and soldering to get the stock connector swapped on. The ESG636 can be installed in the Ninja 250's case, but it will "require some machining of the case." More-specific information isn't available at this time.

For the time being, a stator swap should be considered an expert-level modification, not suitable for most mechanics. If you're comfortable with soldering and have access to heat-shrink tubing (electrical tape is not an acceptable insulator for this job), and are capable of jobs such as a valve adjustment, you have the skill to swap in the ESG110. If you're willing to commit your engine cover to having at least 4mm machined off the stator mount-points, the ESG636 should be achievable. If considering either modification, contact Electrosport directly for more-specific fitment information.

This FAQ article should not be considered authoritative on the matter of stator installation.