Hello,
My father owns a golf cart. Today, he noticed that the charger was not working anymore. The cart, now dead, had to be hand loaded onto a trailer and hauled away. He said that he'd have to spend several hundred dollars to get a new charger. As I'm studying to become an EE, or so I hope, I suggested that I would fix it and he'd devote the money to my education.
Now I understand basic circuit troubleshooting, and I'm confident I could fix it. It's a basic transformer-type lead-acid battery charger (6x 6v batteries), with a little bit of digital circuitry to control the state of the charger and the current flowing through it.

What I'm rather unclear on is how to get the charger to try and "start up". Normally, you'd plug it into the golf cart, but if I wanted to use it with my oscilloscope (I'm assuming I'll need to use the oscilloscope), I'd have to move the charger inside of the house.[1][2]

So my question is, what could I use as a stand-in for a battery pack? [3]

Thanks!

[1]: IMHO, it's too hot outside for the oscilloscope at 89F in the shade -- and the trailer isn't in the shade.
[2]: Yes, I know. I have to prevent ground loops when probing.
[3]: I didn't search online for an answer. I'm trying to be prudent so as to avoid blowing up the charger and/or hurting myself. I did try and search the forum, but the search function still only gives me blog post results.

 

Typically, golf carts run on lead acid batteries. You don't need an oscilloscope to trouble shoot the charging system. A DMM should be enough.

First step is to find out how many batteries are in the cart, the voltage on each battery, and how they are wired together.
This will give you the output voltage required from the charger.

Your second step would be to measure the voltage on each battery.

The third step would be to measure the voltage output of the charger both when not on a load and when connected to the batteries.

 

Typically, golf carts run on lead acid batteries. You don't need an oscilloscope to trouble shoot the charging system. A DMM should be enough.

First step is to find out how many batteries are in the cart, the voltage on each battery, and how they are wired together.
This will give you the output voltage required from the charger.

Your second step would be to measure the voltage on each battery.

My original post lists them as 6x 6v batteries. Maybe I should shorten the post?

The third step would be to measure the voltage output of the charger both when not on a load and when connected to the batteries.

Don't I have to create a circuit diagram after examining the charger and checking for any obvious signs of damage to the circuitry? I mean, we already know that either the output voltage or amperage or both are incorrect.

 

My original post lists them as 6x 6v batteries. Maybe I should shorten the post?

Don't I have to create a circuit diagram after examining the charger and checking for any obvious signs of damage to the circuitry? I mean, we already know that either the output voltage or amperage or both are incorrect.

You don't have to shorten the post. I have to scan through about 100 posts daily. I can easily miss important details in a quick scan.

Trouble shooting in electronics takes meticulous detective work. You don't assume anything without actual verification.
As I said, measure the voltage on each battery.
Measure the total voltage of all 6 batteries.
Measure the output of the charger while disconnected from the batteries.
Measure the output of the charger when connected to the batteries.

If you seriously want to become an EE it pays to pay attention to details such as this.

 

Please do not make substantial edits to your posts because this would put follow up replies out of context and make them meaningless.

 

<snip>
Trouble shooting in electronics takes meticulous detective work. You don't assume anything without actual verification.
<snip>

If you seriously want to become an EE it pays to pay attention to details such as this.

Hmm, good point.

 

All 6 batteries are at 6.0-6.1 volts.
The charger doesn't output any voltage when it's not connected to the load.
When connected to a load, I get a variety of readings. My DMM, when first connected, reads 7.4v. Then it quickly falls to 4v. Then to 3v. Then to 2v. Then to 1.7v, where it goes up and down a little bit back to 3v or so.
Edit: Measurements of the output voltage of the charger were taken before it goes into the cord to the golf cart.

My DMM is a True RMS meter TA801C. I'll post pictures of the charger.

 

There might be nothing wrong with the charger. Most chargers these days have some "smarts." They measure the voltage of the pack when you hook it up and if the pack isn't within a certain voltage window it won't apply any charging current. This is because, let's say it's a 36V pack but the charger only detects 31V; it could be because each battery has discharged to 5.17V, or it could be because one of the batteries is down to 1V because it has bad cells, while all the others have 6V. You apply charging current to that, it could blow up the bad battery.

Once a cart goes below the point where a charger will still charge it, you have to get creative. I recently "fixed" a friend's "dead" cart by taking all the batteries out of series, putting them in parallel, and trickle charging the whole pack for a week as if it were a single 6V battery. I used my bench cc/cv power supply to do it.

 

All 6 batteries are at 6.0-6.1 volts.
The charger doesn't output any voltage when it's not connected to the load.
When connected to a load, I get a variety of readings. My DMM, when first connected, reads 7.4v. Then it quickly falls to 4v. Then to 3v. Then to 2v. Then to 1.7v, where it goes up and down a little bit back to 3v or so.
Edit: Measurements of the output voltage of the charger were taken before it goes into the cord to the golf cart.

My DMM is a True RMS meter TA801C. I'll post pictures of the charger.

Something is wrong with the cord to the golf cart. From the point you are measuring, you should be able to measure 36V from the cart, even with the charger turned off.

 

Something is wrong with the cord to the golf cart. From the point you are measuring, you should be able to measure 36V from the cart, even with the charger turned off.

Under normal operation, the charger has a relay or something inside you can hear go "click" when you connect it to the golf cart's battery. It then starts to make a buzzing noise.
BTW: It's still making those noises, it's just that the batteries don't charge for whatever reason.

 

Oops, I misread what you said. Yes, the cart's batteries are currently at a combined 36v.
(It's late. I need to go to bed.)