View Full Version : Battery charger - strange problem

December 5th, 2009, 02:00 PM
I have a new 20 kw air cooled model 0055251. The charger is installed in the RTSN transfer switch and is outputting 13.6 volts. The charger feeds the generator control panel with its own Tex cable with 14-2 wire guage.

I have checked and double checked the terminals used to connect the charger to the generator. The positive lead is connected to terminal 15B and the negative lead is connected to "0 DC common" I measure the correct voltage and polarity on the terminal screws. Terminal 15 B has a second wire under the screw which it should have accoring to my manual.

When I disconnect the battery cables I get 0 volts accross the battery cable terminals. My manual says I should see the charger voltage.

When I connect the battery I am prompted to go thru the normal date time etc set up. The 7.5 amp ATO fuse is OK.

I do not yet have a gas connection but I dont see where that would affect the battery charging.

Can anyone offer advice.

Thanks Dave

December 5th, 2009, 03:20 PM
I'd have to check to be sure, but the battery tender on my motorcycle has no output until its connected to the battery. Your charger may be the same. I don't believe you'd get 13. 6 volts without charger output to the battery.

December 5th, 2009, 04:41 PM
Lift both wires coming from Transfer Switch to Generator off of terminals where they're landed and check voltage. If none, you have a open(s). If charger voltage is read you have a short.

December 5th, 2009, 04:45 PM
While your comments may apply to some chargers, the Generac one specifically, in section 3.1.4 Operational Testing, requires that the cables are removed from the battery before checking voltage
Thanks for your reply.

December 5th, 2009, 04:58 PM
Possibly I wasn't clear. You'd be checking voltage across the (2) disconnected conductors from the charger. Not the terminals. Battery connected or not has no bearing.

December 5th, 2009, 10:15 PM
I have charger voltage at the generator terminal strip so the circuit between the charger and the generator is neither open nor shorted in my opinion. What is not happening is for the charger voltage to be applied to the battery. The charger installation manual says I should be able to read charger voltage across the battery cables with the cables disconnected from the battery.
From the terminal strip, the charger voltage seems to go into the electronics with the manual auto off switch but does not come out to the battery.
The manual is very clear on the specific test being done with the battery disconnected.

December 6th, 2009, 12:29 AM
Yes, you should see voltage from the charger at battery cables when disconnected from the battery. You said the control panel is still powered though when the battery cables are disconnected? I would start checking the 13 wire for continuity. You should be able to pick it up at the starter contactor and trace it back to where you lose voltage.

I just recently had a unit wired wrong from the factory. They landed the wires on the wrong terminals factory side.

December 6th, 2009, 06:34 AM
My experience has been that you get 0 output from th charger until it receives battery voltage or draw I am not sure which it is. I then would lift the negative off the battery and test voltage at the cable ends. I now just check for 13 or more volts at the battery with everything hooked up. I am not sure but the new control board self test feature may disconnect the 12 volt input circuit from 15B when the battery is disconnected. I will experiment on my next unit.

December 6th, 2009, 11:46 AM
While your comments may apply to some chargers, the Generac one specifically, in section 3.1.4 Operational Testing, requires that the cables are removed from the battery before checking voltage
Thanks for your reply.

(I don't have said manual, so I'm speaking from experience...not fact)

I would read that as....remove cables before checking BATTERY voltage. If you don't remove the cables, you'll actually be reading charger voltage when in fact the batt may be weak.

All "smart" chargers that I have seen need to have a battery reference voltage so they can determine how much the charge level should be. If no reference, no charge.

"ohmslaw...I now just check for 13 or more volts at the battery with everything hooked up"

That works for me as well because the batt won't make more than 12.8 or so with the charger disconnected. Check the batt voltage with terminals disconnected and then reconnect and test again. If voltage is up after reconnecting the terminals...your charger is working.

Edit: If you have charger voltage at the terminals in the unit with the battery disconnected....disregard all my suggestions and start tracing wires as mentioned earlier.

December 6th, 2009, 04:36 PM
I finally figured out what was going on. The manual that came with the Generac Charger is WRONG. It tells you to check the charger with the battery leads disconnected and even shows a picture of the test being done with a battery lead disconected.

When tested like this my charger failed which did not make sense as it had 13+ volts at the terminal strip in the generator.

I downloaded and read the Generac Troubleshooting manual. I have pasted the important section below.

“RT SN & RT SE Transfer Switch”
The battery charger is supplied with 120 VAC. The
output of the battery charger is 13.4 VDC/2.5A.
Refer to Figure 12 or Figure 12A.
1. Set VOM to measure DC voltage.
2. Remove and isolate battery charger black and red leads
from generator terminal strip points G and H.
3. Measure across points G and H. Battery supply voltage
(12 VDC) should be measured.
a. If battery voltage is not measured, wait 5 minutes
and repeat Step 3. If battery supply voltage is still
not available, refer to Flow Chart.
b. If battery voltage is measured, proceed to Step 4.
4. Reconnect battery charger black and red lead wires
previously removed in Step 2.
5. Measure across points G and H. 13.4 VDC should be
a. If 13.4 VDC is not measured, replace the
battery charger
b. If 13.4 VDC is measured, the charger is working.

My installation passed this test. I hope someone from Generac takes note and updates their charger manual.


December 6th, 2009, 05:05 PM
A vehicle (or generator in this case) battery will sit at about 12.6 volts at rest (after it has been off a charger for several hours).

If you are measuring the battery voltage and it is higher than that (13.6 volts in this case) it indicates that the charger is working.

A lead acid battery is a constant voltage charge type (as compared to NiCad batteries that are a constant current charge type) as so is properly charged by applying a constant voltage as per the battery manufactures spec. If the battery voltage after it has been on charge long enough to reach full charge (I would say a week) is correct according to the battery manufactures specification for "float voltage" then all should be good. I would think that 13.2 to 13.4 volts would be a proper voltage for float of a wet cell battery.

December 9th, 2009, 08:48 PM
I had the same problem on my 20K unit I just installed. I called Kelly and he said that you should just remove the positive cable and check with a Meter to the positive on the wire and the ground on the battery. I haven't done it yet but the Generator contol panel and wireless control panel read that the battery is charging and ok. Was there a picture in the Manual?

December 19th, 2009, 09:08 PM
Yes there is a picture in the manual showing the test as Kelly described... I did that and there was no voltage. I have not studied the wiring diagram but suspect that the electronic control is between the battery and the charger terminals. No battery connected means that the circuit is broken and you will not see the charger voltage. Do the test at the terminal strip and you will see what I mean.

December 20th, 2009, 08:03 AM
A word of advice. Always remove the negative cable first, not the positive.

December 20th, 2009, 08:08 AM
A word of advice. Always remove the negative cable first, not the positive.
TimAnd your reasoning is...? Just curious.

December 20th, 2009, 09:01 AM
You never remove the positive first from any negative ground system. The chance of hitting your wrench to ground is to great. You remove the ground and then the positive. The positive always goes on first. I have seen the screens on the inside melted from not following this advice. The screens get big holes in them real fast. I also have a strict policy on battery installation. The battery goes in with the neg plastic cap still on the post. The cap stays on until they positive cable is secured and covered with the Generac supplied cover. this eliminates the chance of dropping the wrench across the terminals, then the negative cable goes on. You can check the charger voltage across the disconnected neg. cable to the positive and get the same reading regardless of what generacs manual reads. If their test says to remove the positive cable that is unsafe and should be ignored. My policy came about because I smoked a nice leatherman across the two post when I was prying the positive terminal open to allow it to fit on the post. Since then we leave the negative post cap on for safety .

December 20th, 2009, 09:11 AM
Interesting thoughts. I had not thought about the tool(s) shorting out the battery, as I've never had a problem or even a close call with that.

December 20th, 2009, 09:39 AM
I too subscribe to Ohmslaw's line of thinking though I have never come close to shorting tool across terminals I have had a tool slip while removing the positive terminal and touched the frame. I was so thrilled that I had disconnected the negative first.

December 20th, 2009, 09:52 AM
Coming from a mechanic background the rule "Negative Off First" - "Negative On Last" is one of the first things you learn when working with batteries. If you ever short the battery could explode in your face. Keeping protective caps on is also a great idea.

Another good rule...always wear safety goggles when working with any lead acid battery. I have seen brand new batteries and old batteries explode for no reason. Better safe the sorry.

December 20th, 2009, 11:20 AM
While I don't disagree with the idea in the above posts, it's rather interesting that Generac built my 5416 generator in a way that the positive cable is the only one which is readily accessible.

The positive cable is not even long enough to allow me to pull the battery out far enough to get to the negative cable clamp. I have to first remove the positive cable from the battery and then I can pull the battery further from its normal position to get at the negative cable clamp.

The negative cable is not long enough to allow me to reverse the battery's position so that the negative cable connection becomes readily accessible for the first disconnection.

Maybe another mod is in order.... :rolleyes:

By the way - in an automobile, I have usually removed the negative connection first. I just never gave it a lot of thought.