Wiring Battery Status Meter to Switch

[ezgovstar]

I have a 1989 36v EZGO Marathon resistor cart. I'm trying to wire a battery indicator to monitor battery charge. I've reviewed the wiring diagram, watch many You Tube videos (not specifically for my cart) and can't seem to figure out how to wire the "C" terminal. It says to wire it to the key switch. But I get no voltage on either terminal with the key in either of 2 positions. If I wire the "C" terminal directly to the 1st battery then the meter works. But I don't want it constantly on. The switch does something, because the cart won't move with it in the off position.

I can always add a two position switch in the "C" terminal wire, but that seems ignorant. Or, (and maybe this is the intended way) I can come off the "+" battery terminal to one lug of the switch, and off the other switch lug, run the wire to the meter. But I'm sure this is the right way. Anyone have any experience with this?

[JohnnieB]

The keyswitch in a resistor drive Marathon is not directly connected to B+ or B-.
The solenoid's coil and pedal switch is between the keyswitch and B+ while the motor's stator windings are between the keyswitch and B-. (see attached schematic)

Using a DPST keyswitch like the ones used for factory installed headlights in later EZGO carts, is the only why to shut the meter off with the keyswitch. Or a separate SPST switch for the meter could be used.

[ezgovstar]

Thank you JohnnieB.. Looks like I can get that key switch from Amazon for $21. I think I like that option better than a second switch or just allowing the battery indication to be powered all the time. Also beats me banging my head on the driveway. :)

[Timberwolflt]

I like my meter constant on... I can glance at it anytime I walk past and it ain’t like that LED is drawing any power to speak of... Probably take it 15 years to drain the pack any noticeable amount

[ezgovstar]

I was curious about the draw. I didn't think it was much, but my cart will sit for long periods. Suppose it's insignificant when compared to how much battery it takes to operate.

[Sideways]

I have my LED digital meter wired to be on constantly as well, mainly so I can glance at it while I am charging the batteries.
It is also convenient to see if I have to reconnect my DPI charger if I don't use the cart for a week or so to top off the charge.
As in everything, it is all personal preference.

[Timberwolflt]

If your cart sits for long periods... you have to top off the charge anyway periodically to avoid battery damage... I really doubt the meter makes any difference at all

[JohnnieB]

IIRC, the dash mount DVM I got from Scottyb back in 2011, draws about 5ma, so it'd take about 22,500 hours to drain a 36V pack of T-105s down to 50% SoC.


The batteries in and of themselves, self discharge at about 1% SoC per day. (94ma discharge rate)

[ezgovstar]

There is no doubt that I have mistreated my batteries. This is my first cart, the batteries in it I put in new in 2011. It spends the winter outside (until now, it’ll be in garage) so the batteries have been exposed to freezing temps. So part of what I’m doing is to prep for better battery care when I replace these. I appreciate everyone’s thoughts.


Sent from my iPhone using Tapatalk

[JohnnieB]

Being exposed to freezing temperatures (IE: +32°F and below) doesn't hurt lead-acid batteries as long as the temperature doesn't fall below the freezing point of the electrolyte, which varies from about -78°F for fully charged batteries up to about +4°F for batteries at 50% SoC.

The trick is to charge them up once a month or float charge continuously when the cart isn't being used.

Cold batteries have less storage capacity and less ability to produce amps. A 225AH cart battery that is rated at 80°F, only has a storage capacity of about 112AH at 0°F.

Keep the batteries charged to 70% SoC (-15°F freeze point) and higher during the winter and they'll be fine in Gastonia, unless the temperature drops abnormally low