Solenoid diode.

[Texas_Electric]

My 89 Marathon does not have one, but it's a series resistor cart. I can see why a solid state controller would need one. Does a resistor cart need one as well?

Thanks!

[cgtech]

NO, that would be bad, it would always be hot trying to push golf cart.

[radioman]

As info Diodes are used across relay and solenoid coils to clamp inductive reverse voltage spikes when the coil is de-energized. The voltage spike is caused by the magnetic field collapse into the coil when the voltage is removed. The diode is connected so it don't conduct on applied voltage. The striped end is the cathode and is connected to the positive applied voltage so it does not conduct. The collapsing magnetic field generates a voltage spike in the reverse polarity of the applied voltage and the diode conducts and suppresses the reverse voltage spike which can be many times greater than the applied voltage.

[JohnnieB]

Just to get everybody on the same page.

The solenoid in all golf carts should have a diode connected across the small terminals for the reason radioman stated.

However, there should not be a pre-charge resistor connected across the larger solenoid terminals in a Resistor drive cart for the reasons cgtech stated.

The cart will run without either device, but they reduce the arcing on the contacts of upstream switches and the solenoid contacts in carts with electronic speed controllers, which in turn prolongs the lifespan of those components.

[cgtech]

I was mistaken (read wrong), we werent talking about resistors. Question for JohnnyB: the resistor coil cars have no ESD sensetive devices to protect, what would the purpose of the diode be in a system that has no microprocessors, transistors, ect. I know the voltage can spike to over 1kv, but it doesnt have the power (amps backing up the spike) to even light a light bulb.

[JohnnieB]

Originally Posted by cgtech

I was mistaken (read wrong), we werent talking about resistors. Question for JohnnyB: the resistor coil cars have no ESD sensetive devices to protect, what would the purpose of the diode be in a system that has no microprocessors, transistors, ect. I know the voltage can spike to over 1kv, but it doesnt have the power (amps backing up the spike) to even light a light bulb.

It protects the contacts in whatever switch opens to de-energize the solenoid.
Typically it is the pedal switch, but the keyswitch or the microswitch on the F/R can be the first to open.

What happens is that the switch contacts open at mechanical speeds and the spike occurs at near the speed of light. Basically, the instant the contacts open, current stops flowing through the solenoid coil and the magnetic field collapses, generating a high voltage spike with the opposite polarity while the slow moving switch contacts are still in arc-over distance physically.

True, the ampacity of the spike is low, but it is still enough to pit the switch contacts and cause them to fail sooner.

[cgtech]

Gotcha, diode = happy microswitch Why no diodes on gas cars?

[Texas_Electric]

Thanks for the info. I have one on the way from Golf Cart King, plus talk few other goodies........

[JohnnieB]

Originally Posted by cgtech

Gotcha, diode = happy microswitch Why no diodes on gas cars?

I don't know diddly-squat about gas carts, but in general terms the DC coils of all solenoids, relays and contactors ought to have a diode across them.

Might be because they probably operate on 12V , which won't generate as high of a spike as 36V and above. But that is just a guess.


EZGO didn't put a diode on the solenoid in a PDS cart either. Both sides of the coil is fed by the controller, so there is no mechanical switch contacts and some protection for the electronic switches probably exists inside the controller, but adding a diode to it certainly won't hurt.

The DCS controller has a diode, but it is in parallel with the pre-charge resistor across the contacts rather than the coil, which makes no sense to me. The solenoid coil is energized/de-energized by the controller also, but can also be de-energized by the keyswitch and a microswitch on the F/R assembly, so the coil needs a diode.

[tculpepper]

Johnnie B, would putting a diode on the solenoid of my resistor cart possibly help resolve all of the arcing issues I've been having with my wiper board?