Intermittent loss of power question

[crash51730]

I haven't had a chance to really dive into this problem, but I wanted to bounce it off you guys first. It helps having a place to start. Cart info 1998 ezgo medalist. Long travel 6 in lift, 23" tires, recently installed scottyb's 2g cables, 500a alltrax controller and heavy duty solenoid. We are still running on the 36 v setup, batteries are 4+ years old and can only get them to about 85% soc. the cart will lose power for a second then regain power. It seems to occur during all phases of acceleration but seems worst in the middle of accelerator travel. It also seems to be possibly happening when hitting bumps in the road. But it has also occurred on relatively smooth riding. Power just cuts out then comes right back to regular power. The problem occurred before all the Scottyb upgrades as well so all of those connections I have high confidence in. I don't hear the solenoid dropping out when this occurs. But you can see the voltmeter jump up like all the load is off the motor. Is it possible for the ITS to have a dead spot, or for it to be malfunctioning over bumpy travel?

[JohnnieB]

After working on electrical and electronic devices for over half a century, I can assure you that anything that can go wrong, will go wrong.

What type motor does your cart have, series or sepex? (AXE or DCX Alltarx conteroller?)

Did you replace all the high current cables? (13 on a series, 10 on a sepex)

You'll to have to monitor some voltages while the cart is moving to find the problem, so pick up a set of clip leads like those shown in attachment from Radio Shack or wherever you can find them. They don't have to be exactly like those shown, but they do need covers over the alligator clips so they don't short something out if they move around while the cart is in motion.

Using insulated clip leads, attach your DVM's negative test lead to the battery pack's main negative terminal and the positive test lead to the white wire to the ITS. The voltage on it should vary with pedal position.
If it doesn't, try the black wire to ITS. (One of those two ought to vary with pedal position.)

If that voltage is staying steady while cart is misbehaving, the ITS is probably OK.

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Next place to monitor is between M- at battery pack and the B+ terminal on controller.

That voltage may rise some when cart misbehaves because pack voltage increases when it is unloaded, but it shouldn't drop any.

If it is stays the same or increase a bit, the controller is doing its thing correctly and there is an intermittent open somewhere in the high current loop.

Motor brushes, maybe?
Cables to motor? (If they haven't been replaced.)

[crash51730]

It is a sepex motor. I also did replace all 10 cables with ones from scottyb. The only cables to the motor that were not replaced were the 2 motor field wires. It does seem when the problem occurs, the pack voltage jumps back to NEAR standing voltage. Then drops when the motor picks back up. I have a digital dash voltmeter installed so it is pretty useful in that regard. I am going to dig into it this weekend. Just wanted to try and find a couple of places to start.

[JohnnieB]

Having a sepex motor adds another possibility to the list, but easy to check.
Just connect the DVM across the F1 & F2 terminals and monitor the voltage.

I screwed up on which terminals to monitor, should have been M- and B+.
I corrected it in my earlier post.

If the solenoid is staying activated while the cart is misbehaving, that pretty much narrows it down to an ITS issue, a motor issue or the F1/F2 cables.

Yep, the DVM on the dash is a handy little gadget.
You've got a high amp controller, so you might want to keep an eye on how far you are dropping the pack voltage under load.
Try to stay above 1.75V per cell (31.5 for a 36V pack) while accelerating and climbing.
Only take them down to 1.5V per cell (27.0V for a 36V pack) in dire emergencies, like getting off the tracks when a train is coming at you.

[scottyb]

Just a hunch..... these carts have a built in flaw. The motor wires pass through a steel loop which sometimes rubs the coating off of the wires and causes a short. I have seen this in my service work time and again.
This loop is located on the passenger side of the cart at the rear of the battery box.

See pics and check it out.

[JohnnieB]

Thanks Scotty,

I'll make sure to take a close look at my F1/F2 cables while I'm cleaning/painting the battery rack.

I inspected the ends closely when I replaced the high current cables, but don't remember looking at the stuff in between.

[razor1]

Check your key switch. Just had one go faulty on me and it caused the exact same symptoms.

[scottyb]

Everybody with a TXT should check their cart... you see the loop in the pic it is typically mounted to the corner vertical of the battery tray. I prefer to slide a 4-6 inch piece of agricultural drip tube over the wires (where they pass through the loop) to prevent chaffing. The drip tube is tough stuff and I slit it and zip tie it in place. A hole in each end of the tube to run the zip tie through guarantees the tube will stay in place.

[razor1]

Scottyb - Is that the rear passenger side battery frame upright in the picture?

[Taykol]

Yes
Was just looking at mine 5 minutes ago