while cleaning out the barn I found a new Ford cutout , #BONN-10505-A , most likely for our Ford 9N we once had , could this be used on a T ? thanks
I've been told by a very knowledgeable electrical engineer that the best thing to do with those is to duct tape them to a cinder block. Go to a very deep lake, and toss the cinder block in.
If the cut out dies open it can fry the generator.
Can you help me on this one?
We still have an N and I use a cutout on a 1935 V8 since I got it over forty years ago as well as a '25 touring.
I also know what to do when a cutout does not operate as it should regardless of what it is on.
What I have been unable to determine is the following:
Is the FP diode type cutout a voltage regulator?
I am talking "voltage regulator" in the sense of delivering to the battery what is necessary to maintain a full charge level.
I believe the answer to the above question is no because the amp rate is still "regulated" by the third brush even with a diode type cutout.
Ken in Texas
We make BOTH cutouts and Voltage Regulators. On the outside they are identical but on the inside they are not at all alike nor do they function the same. The T cutout we make (P/N 5055) is a diode cutout and has no ability to change the charge rate from what the generator setting is. If the generator third brush is thus set to charge at 4 amps then that will be more or less the constant charge rate whenever the generator is spinning fast enough to put out 4 amps and the third brush is regulating that rate to 4. in this cutout setup the voltage out of the generator is not regulated so when the battery is fully charged the constant 4 amps will not reduce but will overcharge the battery. The battery terminal voltage will go higher and higher with overcharge and eventually electrolyte in the battery will boil away unless the overcharge is kept rather small hence the 4 amp setting.
The VR we make for the T (P/N 5055R or S5055R) operates differently. The charge rate setting of the generator is typically setup to put out enough current to carry the headlights at about 8-12 amps and the charge rate will be at that setting during driving only until the battery is fully charged and then the VR will reduce the charge rate radically to prevent any overcharge. It can and will reduce the final charge rate to below 4 amps even when the generator charge rate is set to 12 amps. Thus it allows a higher third brush setting that charges at a higher charge rate to quickly recharge the battery after starting but then reduces it to only the amount the battery wants in order to maintain its output at full charge. Thus the cutout requires the generator to be set low because it is a constant rate and can result in overcharge while the VR allows the generator charge rate to be safely set much higher because it will lower the setting once the battery is fully charged as determined by the battery voltage hence the term "voltage regulator". The purpose and overall function of the VR is the same as the VR on you modern car. On modern cars the VR is generally part of the alternator and built into it. It doesn't matter where it is and early alternators had an external voltage regulator much the same as the later 2 brush generators did.
I have a question about your VR. If you set your generator to 12 amps, (6V system), start with only a partially charged battery, or even a fully charged battery, and are using "stock" head and tail lights and driving for an hour or so at night, wouldn't you run the risk of overheating your generator? For how long can a 100w "T" generator supply 12A @ 6-8V safely? I drive at night quite often with our local model A club and would love to avoid running at night at -5A for any length of time.
I take it the 5055 and 5055R both have a diode and it is the diode that protects the generator.
Are the diodes replaceable or do you just get another unit?
Other than hooking up a 12 volt battery to a 6 volt unit or having the battery cables reversed, etc., what is the main threat to a diode under normal driving conditions?
I can't speak for other cutouts but it isn't the diode that is in danger if you increase the current beyond the 15 amp rating of the generator. The generator is going to burn out first unless there is something radically wrong in the wiring in which case the wiring might smoke first. I have my own generator set at just over 12 amps on a 1% accurate ammeter and that generator has been set that way for over 50K miles on my T. It was installed in the late 80's and I have not re-adjusted it since that time. The generator can handle 100 watts continuous but the battery cannot take that much overcharge and will boil away. Everyone is terrified of driving with ANY discharge at any time. If driving at night with a proper setting of the third brush as directed with the instructions you will run out of DARKNESS and will be hit by MORNING long before your battery notices anything. Most issues that are discussed are hypothetical and overthink is the real problem. I suspect many of the VR's are not likely adjusted correctly because the owners have a "different and better" method. So long as the final setting is less than their generator can handle (100W) there is no consequence other than a long time interval in recharging the battery. This will shorten battery life somewhat but is probably not serious.
I wasn't addressing the diode - I think that was Ken. I was just questioning if the "T" generator could put out 100W continuous, putting out 12A at, what I assume, is about 8V. Your experience is it can, without overheating, and that is great news. Looks like your VR is the answer.
Modern batteries should not be subjected to 8V charging or they will be hurting. It does appear that when charging batteries during the T era it was common to subject those batteries to more than 8V. I sometimes wonder if that didn't contribute to their short life. The 100 Watt limitation on model T generator is usually taken as up to 15 amps when charging at 7V (preferably limited to 7V max). The problem is that many of the ammeters are not that accurate and were spec'd at 5% when new on the large meters (19-25) at full scale. On the small meters (26-27) the spec said they were to be within 1 amp at 10 amps which is 10% accurate but not really specified at full scale which is the norm. It is risky to assume the ammeter reading is dead accurate.
Thank you for your reply. From what I have read on this forum from you over the years, I do consider you THE EXPERT! I am always surprised by how few very "mechanically inclined" people really understand basic electrical theory.
Am I wrong to assume that with an electromechanical or a diode cutout, the voltage applied to a 6V battery by an unregulated T generator would be determined by the internal resistance (the condition) of the battery in the circuit? A sulphated battery may allow 8-10+ V at a reduced amperage.
Does your VR limit the charge voltage to 7V regardless if IR, or simply cut the amperage down when a full charge (6.3V) is reached?
To be totally accurate the charge voltage is monitored and regulated to near 7V at all times. The ambient temperature will have an effect on the voltage a wee bit since the main job of the VR is to provide maximum battery life and the battery benefits by the charging voltage changing with changing temperature according to small voltage change being made for each degree of temperature change that happens. A fully charged 6V battery that has not been charged or discharged for 48 hours will read about 6.35-6.38 V in a 70 degee F ambient temperature. When you first stop charging the battery you will be removing it from a 7V source and it will not immediately go to 6.38 V but will slowly drift down to that voltage. Hence if you measure a battery's voltage with a digital meter it can read much higher and you MUST know the battery state of the previous 48 hours or you can get fooled about its charge state. 48 hours is the absolute for sure time to use but you can generally read a battery after 24 hours off of the charger and get a close approximation. If after you remove a battery from charge its voltage drops below 6.30 then it is not fully charged and you don't have to wait another long time to know that. Just be aware that lead acid battery terminal voltage is not useful as a charge measuring stick unless you know the immediate previous 48 hours since the battery voltage drifts slowly down and needs a lot of hours to fully settle down. Final voltage can also vary a small amount so write down the full charge voltage of your new battery and use that as your reference.