Having trouble diagnosing a couple of electrical issues with this scooter. I would appreciate some assistance in determining whether the charger is (or is not) outputting the required voltage and how the failure of the ammeter (onboard) to register any amps during charging is (or is not) related.


This is a 24 Volt scooter. The two batteries have been tested as okay. The voltage readings discussed here are taken with a Voltmeter connected across the battery terminals. The on-board charger is a 24V DC charger with a 29.4 V max rating output. The on-board ammeter has a black and red wire connected to the rear of it with these two wires leading to the output harness of the on-board charger. This scooter also has an on-board voltage gauge.


The first issue is the on-board ammeter is not functioning. It is supposed to indicate 1 or 2 amps when the on-board charger is plugged in depending on how drained the batteries are. The batteries have been drained to various levels without any movement of the ammeter needle when the charger is plugged into ac power.


The second issue is the batteries will not hold a full charge. After charging for 8 hours or so, the on-board voltage gauge will indicate 25 volts or so, but very little usage will drain off 2.0 volts. The batteries take a charge but never reach more than 12.7 to 12.8 volts each. (As measured with a Voltmeter.)


Voltage readings have been taken across the battery terminals with the charger connected and disconnected with a 0.1 V difference. This 0.1 V difference between charging and not charging test occurs at most every level of battery charge state.


I am not sure how to go about testing the charger voltage output other that across the battery terminals. Seems to me with the batteries in a 70% drained state I should get more than 0.1 V difference in voltage readings between charger plugged in and not plugged in.


Do I have a faulty on-board charger or on-board ammeter?

 

If the batteries aren't new, take them to an auto parts store and have them tested (unless you have a load tester on hand).

You can check the charger by putting a 1A load on it.

If batteries and charger both checkout, you've found the problem.

 

Having trouble diagnosing a couple of electrical issues with this scooter. I would appreciate some assistance in determining whether the charger is (or is not) outputting the required voltage and how the failure of the ammeter (onboard) to register any amps during charging is (or is not) related.


This is a 24 Volt scooter. The two batteries have been tested as okay. The voltage readings discussed here are taken with a Voltmeter connected across the battery terminals. The on-board charger is a 24V DC charger with a 29.4 V max rating output. The on-board ammeter has a black and red wire connected to the rear of it with these two wires leading to the output harness of the on-board charger. This scooter also has an on-board voltage gauge.


The first issue is the on-board ammeter is not functioning. It is supposed to indicate 1 or 2 amps when the on-board charger is plugged in depending on how drained the batteries are. The batteries have been drained to various levels without any movement of the ammeter needle when the charger is plugged into ac power.


The second issue is the batteries will not hold a full charge. After charging for 8 hours or so, the on-board voltage gauge will indicate 25 volts or so, but very little usage will drain off 2.0 volts. The batteries take a charge but never reach more than 12.7 to 12.8 volts each. (As measured with a Voltmeter.)


Voltage readings have been taken across the battery terminals with the charger connected and disconnected with a 0.1 V difference. This 0.1 V difference between charging and not charging test occurs at most every level of battery charge state.


I am not sure how to go about testing the charger voltage output other that across the battery terminals. Seems to me with the batteries in a 70% drained state I should get more than 0.1 V difference in voltage readings between charger plugged in and not plugged in.


Do I have a faulty on-board charger or on-board ammeter?

If you have medical insurance, they should pay for the repair.

 

Thanks for the replies. Unfortunately the repair is on me for now GopherT.
The batteries have been taken in for a load test and they were ok, auto parts houses do not have the right equipment to load test accurately AGM batteries. At least so I was told. The batteries will take a charge and somewhat hold the charge, just don't think they are being charged fully IMHO. But, I am confused about the failure of the on-board ammeter to function and whether it is related somehow, or involved in the electrical issue. As I posted the on-board ammeter is directly wired to the output of the on-board charger. The little I know of electronics. ammeters must be wired in series I think. The other lead coming out of the charger has 3 wires that go into a white 3 prong connector, which is connected to a connector which has wires that go to the controller and other places.

dl324, how would I put a 1 amp load on the charger and how would I test the charger, other than connecting my test leads across the battery terminals? I do not have an amp meter, only a voltmeter. I probably need to acquire one I suppose. If I had one I am guessing that I could connect the two leads in series with the on-board ammeter(between either the black or red wire connector and the tab the respective wire plugs into on the rear of the on-board ammeter). Or, I could unplug both the red and black wire connectors on the rear of the on-board ammeter and connect each to the respective leads from the Ampmeter (which I currently do not have)? However, as dl324 indicated, I have read elsewhere that a small load needs to be applied to these type of DC chargers for the charger to output a voltage. Not sure how to do that.

thanks for the replies.

 

Measure the voltage at the battery terminals while charging. It should read ~14V.

 

The little I know of electronics. ammeters must be wired in series I think.

Is the ammeter analog or digital? If it's digital, it could be a voltmeter measuring the drop across a sense resistor.

dl324, how would I put a 1 amp load on the charger and how would I test the charger, other than connecting my test leads across the battery terminals? I do not have an amp meter, only a voltmeter.

The simplest way is to put a 1 ohm 30W resistor across the charger. You can calculate current by measuring the voltage drop across the resistor. The charger output should be in the neighborhood of 28V.

If you don't have appropriate power resistors, you could make an electronic load using a voltage regulator like an LM317 (heatsinked) drawing 1A and let the regulator dissipate most of the power. I'll post a schematic when I get to a computer with a schematic editor...

 

Schematic as promised...

Put a heatsink on the regulator (LM317T - I didn't label in the schematic) as it will be dissipating around 18W. It will protect itself, but you want it to draw 1A long enough for you to measure the output voltage of the charger.

R1 and R2 can be 1/4W resistors, R3 needs to be at least 10W. Load current will be about 0.98 amps; you should measure about 10V across R3.

If the batteries weren't being charged properly for an extended period of time, they may too far gone.

 

how would I put a 1 amp load on the charger

Use a 12V 12W (or as near that Wattage as you can get) car light-bulb as the load.

 

Use a 12V 12W (or as near that Wattage as you can get) car light-bulb as the load.

The charger in question charges 2 12V batteries in series.

 

Measure the voltage at the battery terminals while charging. It should read ~14V.

Double that; it is a 24V system, or read each 12V battery separately, and add the two voltages.

Good reference on proper SLA charging voltages.

 

The charger in question charges 2 12V batteries in series.

Oops, forgot that. So, use a 24V (15W-21W) bulb as the load.

 

Here are the specs on the charger, taken from the tag on the base of the device:
Fast charge: 29.4 VDC
Absorption: 29.4 VDC
Float Charge: 27.6 VDC
AC Input: 100 - 240 V - 2.5A
DC Output: 24V - 4A

After charging overnight, with limited usage this am the voltage reading taken across the battery terminals is 11.9V, 12.1V, and across both together is 24.1V. Plugging in the charger I read 12.0V, 12.2V, and 24.2V. After a few minutes of charging the same readings are 12.1, 12.3, and 24.3V.
Based on the specs on this charger, even if the charger was in 'Float Charge' state shouldn't the voltage readings taken across the battery terminals with the charger plugged in be something close to 27.6V? I am only reading 0.1V difference in voltages taken with the charger unplugged and then plugged in.

Thoughts?

 

Double that; it is a 24V system, or read each 12V battery separately, and add the two voltages.

Good reference on proper SLA charging voltages.

Thank you for the reference, I have bookmarked the site. It referenced SLA batteries, this scooter has AGM batteries.

 

Thoughts?

Either your charger isn't working correctly, or it's current limited if the battery is drawing too much current. Is there a current meter on the charger?

PS I see from your OP that the ammeter is reading zero? This could indicate a bad charger. You could try measuring the charger voltage unloaded (batteries unconnected) but some smart chargers won't charge unless it detects a battery. Another option is a load resistor connected through a 24V supply. I recon you don't have any of these items, though.

 

Is the ammeter analog or digital? If it's digital, it could be a voltmeter measuring the drop across a sense resistor.
The simplest way is to put a 1 ohm 30W resistor across the charger. You can calculate current by measuring the voltage drop across the resistor. The charger output should be in the neighborhood of 28V.

If you don't have appropriate power resistors, you could make an electronic load using a voltage regulator like an LM317 (heatsinked) drawing 1A and let the regulator dissipate most of the power. I'll post a schematic when I get to a computer with a schematic editor...

Thanks dl324 for the schematic. The onboard ammeter is analog, it has a needle that is supposed to register 1 or 2 or 3 DC Amperes with the charger plugged in, depending on how discharged the batteries are. According to the scooter manual it will not register if the batteries are fully charged. I believe it is not registering even 0.5A with the batteries less than 80% or 90% charged because the charger is simply not outputting enough amperes for the gauge to register and needle to move at all. Clearly, based on voltage readings taken this am the charger is 'charging' the batteries, albeit very little.

 

Either your charger isn't working correctly, or it's current limited if the battery is drawing too much current. Is there a current meter on the charger?

PS I see from your OP that the ammeter is reading zero? This could indicate a bad charger. You could try measuring the charger voltage unloaded (batteries unconnected) but some smart chargers won't charge unless it detects a battery. Another option is a load resistor connected through a 24V supply. I recon you don't have any of these items, though.

Correct Brownout, I do not have those items. No there isn't a current meter on the charger. Only two lights, that are both green when the charger is plugged in. One light for 'Power' and one for 'Charge'. The color of either light would be red if there was a 'problem'.

 

After charging overnight, with limited usage this am the voltage reading taken across the battery terminals is 11.9V, 12.1V, and across both together is 24.1V. Plugging in the charger I read 12.0V, 12.2V, and 24.2V. After a few minutes of charging the same readings are 12.1, 12.3, and 24.3V.

If you think both batteries are fully charged, they're both bad.

 

If your charger won't work unless there is a battery connected, here is one possible way to test it.

 

Thanks dl324 for the table showing voltages and % charged rates. I agree with the assessment of this table, but. Call me hard headed, one of batteries is just a few months old. I understand one should replace these style batteries in pairs. Well, one battery could be pulling the other down, then again the charger could be going bad and not charging the batteries fully. And the on-board ammeter not functioning either is confusing this issue. On the surface, replace both batteries would seem like a solution. This does not resolve why the on-board ammeter does not function as it should. Testing these style batteries should be done with a SLA battery tester, not what most auto parts shop have.
As I said in the OP, the batteries tested as OK at a local auto parts house. Unable to find a place locally that can accurately test an SLA battery.
Thanks for all the thoughts on this.

 

Have you tested the charger using a dummy load (in place of the batteries) as suggested above? That would show if the charger and ammeter are working.