1977 KX 650 b1 HOT rectifier

First of all thanks for taking a look at my post! Here are the symptoms,, Bike is not overcharging indicating regulator is functioning properly. The red/white wire coming off of the rectifier was getting really hot until I cut and re butted the wire with a new connector and now as far as I can tell istnt getting hot. The rectifier however is hot enough to fry and egg on and could potentially melt wires unless addressed..
Very Hot Rectifier? Any ideas why?

KZ,, sorry, typing too fast!

Your battery needs to be load tested for a bad cell or two. This will cause the charging system to work extra hard.

To get your battery ready for a load test,fully charge it with a motorcycle battery charger,and then take the battery to the shop, there a tech will put a resistive load across the terminals reading the amount of discharge.

Check the connector going to the regulator/rectifier and see if a small gauge brown wire is in the plug. Some bikes have it others may not. This is the sense circuit for most of the Kawasaki motorcycles limiting the amount of current going to the battery.

The connection may have corrosion in the male/female pins or the brown wire circuit has been damaged.

skydailey wrote:

Very Hot Rectifier? Any ideas why?

Yep, I can say with 100% certainty that it is due to power dissipation...... no help, eh?:laugh:

A rectifier only dissipates too much power in two ways:

1) forward conduction (diode on) with too much current going through. The reg will turn the rectifiers ON as much as needed to get the battery up to 14V. Is the battery voltage coming up to 14V? If the batt has a shorted cell, it will cook the rectifiers.

2) OFF STATE (diode blocking) leakage current. A sick, damaged rectifier doesn't turn off completely and has reverse current flow when it should be off and that dissipates HUGE amounts of power because the voltage across it is high then.

No brown wire.. This system is a seperate rectifier and regulator. Two wires going to rectifier "red/white and black".. The battery is only 8 months old so could it still have a shorted cell? Also, one more symptom.. The rectifier gets hotter in neutral/idle than it does going down the road.. Also if im riding and turn the lights on it gets red hot!

I think you need to check your rectifier and regulator. www.kz650.info/ has a free Haynes manual download that has testing procedures for the rectifier and regulator. You'll need to buy a multitester, which are really cheap ($3-10) and can be found at Harbor Freight tools (cheapest), any auto parts store or hardware store. Here's the link to the manual: forums.kz650.info/index.php?topic=1833.0

Hope this helps.

Doesn't matter how old or new the battery is. Get it tested before you cook the regulator/rectifier.A weak,shorted or discharged battery are the number one causes of burnt out regulator/rectifiers.When I worked as a Kawasaki mechanic back in the 80s, I saw a lot of regulator/rectifiers burnt to a crisp from people bringing bikes out of winter storage for a spring ride with dead/bad batteries, jump or push start it and go. The charging system goes into full output to quickly try to recharge the battery and then overheats and kills itself and sometimes takes part of the wiring harness with it.All this could have been prevented with a new battery or simply charging the battery overnight the nigh before.

Battery is very week due to sitting a couple of months. I will charge it and see if it changes anything then get back to you ASAP. Thank you for the info guys! Results coming soon!

One more piece of information that was asked about above.. The battery on a meter while at idle is around 12.67 to 13.5 volts. It is clearly under 14v as metioned it should be above..

The battery won't charge at idle speeds, so you won't read anything near 14v there. 14v at 3000-4000RPM is normal. I'm no mechanic, but have ridden these sinse new and have had a lot of dead batterys and it's never once damaged anything. This is the first I've heard of this. If you charge the battery and it has enough power to turn the starter, the battery is OK. 1977 with the separate reg/rect only was used 1 yr. Probably because it was not that great of system. It may get hot under normal conditions. I think if I remember right the rectifier case has a lot of heat sync aluminum on it? You got the burnt wiring problem fixed, I've seen that a few times and fixing the connectors is for sure the cause of that. If you see 14v charge at 4000RPM and the battery turns the starter I'd call it fixed.

Yeah the fins are to dissipate the heat as it bleeds off un-needed voltage.

Locozuna wrote:

Yeah the fins are to dissipate the heat as it bleeds off un-needed voltage.

SCR regulators don't bleed off voltage, they act as series switches between the current output coming from the alternator and the battery (and the rest of the electrical system). The voltage at the gates of the SCR's is controlled by the regulator, and this voltage determines if the SCR's are turned ON to pass current. If they are OFF, they block and the alternator output is not connected to anything as long as they are off. Basically, the alternator looks like a big current source and the SCR's are voltage controlled switches that allow the current go to the electrical system as needed to charge the battery and feed the electrical loads of the bike.