honda305 Home honda305 Auctions honda305 Gallery honda305 Forum Electronic Ignition honda305 Forum honda305 Forum honda305 Forum honda305 Racing honda305 Literature

Auctions  Mailing List    Registry   Marketplace

honda305.com Forum - FULL SCREEN

honda305.com Forum

Login
□ Search
  □ CLASSIFIED_ADS
□ FAQ 
  □ SEARCH_ADS
□ 
  □ MY_ADS
Vintage Honda Owners,
Restorers, Riders and
Admirers

Ballast resistor for low ohm coil

Charging System, Wiring, Lighting
Post Reply
brewsky
honda305.com Member
Posts: 1769
Joined: Wed Jul 23, 2008 5:21 am
Location: Princeton, WV

Ballast resistor for low ohm coil

Post by brewsky » Fri Nov 01, 2019 8:52 pm

I ordered a new dual-fire coil for my dream and it only reads 1.6 ohms across the primary.

If I add a 3 ohm ballast in series, that should bring the resistance back up close to the original 4.5 of the stock one?

Am I missing a potential problem using this setup?[/quote]
66 dream, 78 cb750k, 02fz1, 09 wing

User avatar
garncarz
honda305.com Member
Posts: 188
Joined: Thu Oct 31, 2013 7:44 am
Location: York, PA

Post by garncarz » Sat Nov 02, 2019 6:31 am

Two issues: (1) Why would you want to purposely reduce the output voltage of the new coil? and (2) At 12 volts, your coil is drawing almost 8 amps. You would therefore need a 100W (really big) resistor. Might want to do some more research.

brewsky
honda305.com Member
Posts: 1769
Joined: Wed Jul 23, 2008 5:21 am
Location: Princeton, WV

Post by brewsky » Sat Nov 02, 2019 7:42 am

!. You are right...I don't especially want to reduce the output of the coil....especially when starting.

2. If I add a 3 ohm resistor in series, that should drop the current to 2.6 amps....assuming the resistor doesn't increase in value as it heats up, which would bring the current down even further.

Maybe a switch to short the resistor for cold starting only?

Maybe I've done too much research!!!

http://www.randakksblog.com/ballast-res ... procedure/
66 dream, 78 cb750k, 02fz1, 09 wing

brewsky
honda305.com Member
Posts: 1769
Joined: Wed Jul 23, 2008 5:21 am
Location: Princeton, WV

Post by brewsky » Wed Nov 06, 2019 5:54 am

Ok, does anyone have the actual primary ohm spec for the OEM coil?

I can't find it in the manuals,,,,I have 2 different original ca77 coils handy, and one reads 4.5, and the other 3.6?
66 dream, 78 cb750k, 02fz1, 09 wing

Geoff Hastings
honda305.com Member
Posts: 235
Joined: Wed Feb 22, 2017 2:59 pm
Location: Epsom, Surrey

Post by Geoff Hastings » Wed Nov 06, 2019 6:29 am

Most set ups using a ballast resistor have it out of circuit when cranking to allow for volt drop at the battery and then have it in circuit to prevent the coil being over powered under normal running. The Honda just earths the starter solenoid via the button when cranking so you might not find it as straight forward as it seems.

brewsky
honda305.com Member
Posts: 1769
Joined: Wed Jul 23, 2008 5:21 am
Location: Princeton, WV

Post by brewsky » Wed Nov 06, 2019 8:11 am

Just thinking out loud here....what about the ballast in series with the coil for normal running, and install a jumper from the hot terminal of the starter to the coil side of the ballast?

That should provide as much voltage as available when starter button is pushed, and cut out when released?

Edit: will not work....disregard
66 dream, 78 cb750k, 02fz1, 09 wing

Post Reply

 


 

CB-77 | CYP-77 | Road Test | Riding Log | Literature | Zen | Marketplace | VJ Survey | Links | Home