I have a Scag Tiger Cat that is a couple years old now. This past summer the voltage regulator lost good ground and it drained the battery. I fixed the bad ground at the voltage regulator, let the mower charge the battery, and didn’t have any more trouble.

It had been a couple months since I’d ran the mower, so today I decided to start it up and allow it to run for a little while. Well the battery was dead (around 10.5 vdc), so I had to jump it off. Once I had it started, I removed the jumper cables thinking I’d see if the battery would take a charge. As soon as I removed the cable, the engine died.

I figured I had a charging issue again, so I removed the voltage regulator, cleaned all of the contact points and put it back together. Still no joy. Soon as the jumper cables are removed, the engine dies. Certain that the engine should run once started, regardless of the condition battery (or even without a battery), I began trying try to diagnose what I thought was a charging system problem. Well, it appears to me that the charging system is functioning correctly. With engine off and ignition on, I have battery voltage on the purple wire (center) at the voltage regulator. With the engine idling, I have 13.09 vdc on the purple wire at the voltage regulator and 15.0 ac on the stator wires. At WOT, I have 14.43 vdc on the purple wire and 37.8 ac on the stator wires with the voltage regulator connected. With the voltage regulator disconnected, I have 45.8 ac on the stator wires.

But still it dies as soon as I disconnect the jumper cables. I could have sworn that earlier in the summer when the battery was drained (at an even weaker state than it is now) that it ran fine with the battery disconnected once I fixed the bad ground at the voltage regulator. Was I mistaken? Is there some circuitry on these machines that requires a battery in order to keep the engine running? Just to check, I disconnected the battery completely, started the engine with jumper cables and soon as I disconnect one of the jumper cable leads, it dies.

Not necessarily. Bad batteries can do that. Happens on full size vechiles all the time.

Charge the battery and try it again. Or even replace it they're not that expensive.
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Bad charging system. How many amps is it putting out to the battery from the purple VDC wire? If you're not running anything the charging system has to be able to sustain the engine running or you would have a run down condition even with a battery in place. Don't disconnect the battery just the jumper cables.

 

Look, the charging system seems to be OK. Depending on how the machine/engine are wired, and what engine ya got : http://www.lawnsite.com/showthread.php?t=144040...... it may or may not stay running.
Some/most motors have a solenoid at the carb and some require 12VDC at the coil module.
Ya need to go over yer wiring, including the ground/s, and get a battery afore ya really screw something up.

 

Get yourself a Battery Tender Jr for each mower you have and plug it in, anytime the mower is in the shop. That'll help extend your battery life and eliminate one variable from your electrical issues. If the LED light on the Tender is always showing a charge condition, it's a given the battery is no good. I'm averaging 9-10 years of battery life, on my mowers and motorcycles, using Tenders.

Anytime a battery is in a state of discharge, it is sulfating. When the sulfation on the battery's plates grows to the point of contacting the next plate, it grounds the cell. I'll just about bet money your battery has done that. It's taking more juice than your engine can produce and is killing the engine when you pull the jumpers.

Always completely charge any battery, before use, via an automatic charger. The slower, the better, which is why I like Tenders. Your engine's charging system will never completely top-off a battery. Lastly, relying on your engine's charging system to overcome a battery's discharged state is very hard on the charging system. It's meant to maintain charge; not completely recover a dead battery. Don't do it.

 

Get yourself a Battery Tender Jr for each mower you have and plug it in, anytime the mower is in the shop. That'll help extend your battery life and eliminate one variable from your electrical issues. If the LED light on the Tender is always showing a charge condition, it's a given the battery is no good. I'm averaging 9-10 years of battery life, on my mowers and motorcycles, using Tenders.

Anytime a battery is in a state of discharge, it is sulfating. When the sulfation on the battery's plates grows to the point of contacting the next plate, it grounds the cell. I'll just about bet money your battery has done that. It's taking more juice than your engine can produce and is killing the engine when you pull the jumpers.

Always completely charge any battery, before use, via an automatic charger. The slower, the better, which is why I like Tenders. Your engine's charging system will never completely top-off a battery. Lastly, relying on your engine's charging system to overcome a battery's discharged state is very hard on the charging system. It's meant to maintain charge; not completely recover a dead battery. Don't do it.

The battery is done. It won't take a charge. But I had the battery disconnected completely from the mower and the mower will not stay running without a good battery connected to it. That seems very odd to me. I've got other small engines, one of which is a Kohler Command CH730, that run fine with no battery connected.

Look, the charging system seems to be OK. Depending on how the machine/engine are wired, and what engine ya got : http://www.lawnsite.com/showthread.php?t=144040...... it may or may not stay running.
Some/most motors have a solenoid at the carb and some require 12VDC at the coil module.
Ya need to go over yer wiring, including the ground/s, and get a battery afore ya really screw something up.

I had assumed that the charging system would provide 12vdc to the fuel cut off solenoid once the engine is running, but perhaps it doesn't. I'll check that. It's an instant kill when I remove the jumper cables, just like I had turned the key off, which could be the solenoid.

It will run fine once the battery is replaced but I still wander if the charging system is working correctly if it will not support the engine without a battery.

Bad charging system. How many amps is it putting out to the battery from the purple VDC wire? If you're not running anything the charging system has to be able to sustain the engine running or you would have a run down condition even with a battery in place. Don't disconnect the battery just the jumper cables.

I'm not sure about the amperage output, as my cheap DMM will not measure anything beyond 500mA. I'll have to pick up a better one and check that. However, just for curiosity sakes, I borrowed the 25amp voltage regulator off of my CN730 and put it on the scag (which has a 15 amp regulator) and got the same result. As soon as the jumper cable is disconnected, it dies immediately.

I'm wandering if there is not something in the interlock module that requires 12vdc directly from the battery and if not present shuts the engine down. But like I said earlier, I could have sworn that it ran fine earlier in the year without a battery.

 

My background is in the powersport industry. There are many machines that will not run without a battery, even with jumpers hooked to it. Also, many will not even fire a plug or injector, without a minimum voltage value seen by the ECM.

Without seeing specs in the service manual, I'm guessing. But, your charging numbers seem low. I think you should be seeing voltage numbers over 14, even at idle. That's what I'm used to seeing, but, not 100% sure with mower engines. I should've caught this earlier.

You should post up all pertinent engine data, so hopefully one of the site's techs will come along and be able to offer correct voltage numbers.

 

It's a simple system, no ECM involved. It's just a basic Kohler CV740. There is a cut off solenoid on the carburetor. It could be that the interlock module shuts off the voltage to the cut off solenoid if it doesn't sense 12vdc from the battery, I'm not sure.

The voltage was 13.09 vdc out of the voltage regulator at idle with the dead battery connected, as well as the jumper cables to a good battery. I assume the voltage was low because the dead battery was pulling it down. It shot up to 14.43vdc at WOT.

Anyway, I'll investigate it further when I get a chance. I just figured someone here could tell me if these mowers were set up to where they would not run without a battery connected.

 

It's a simple system, no ECM involved. It's just a basic Kohler CV740. There is a cut off solenoid on the carburetor. It could be that the interlock module shuts off the voltage to the cut off solenoid if it doesn't sense 12vdc from the battery, I'm not sure.

The voltage was 13.09 vdc out of the voltage regulator at idle with the dead battery connected, as well as the jumper cables to a good battery. I assume the voltage was low because the dead battery was pulling it down. It shot up to 14.43vdc at WOT.

Anyway, I'll investigate it further when I get a chance. I just figured someone here could tell me if these mowers were set up to where they would not run without a battery connected.

Just put a new battery in it and go from there.
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just put a new battery in it and go from there.
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^^^ +1 ^^^

I use 1 battery tender and move it/leave it on each battery for about 1 day/battery every couple of weeks during the Winter.

 

Check your charging fuse should be on the left hand side by the throttle there should be two plugs with fuses in them once you unplug it from the box. Or disconnect the battery and go from the positive lead to the center position on your voltage regulator and ohm.

 

Check your charging fuse should be on the left hand side by the throttle there should be two plugs with fuses in them once you unplug it from the box. Or disconnect the battery and go from the positive lead to the center position on your voltage regulator and ohm.

Both fuses are good and I have continuity between the center terminal on the regulator and the positive battery cable.

It needs a battery regardless, so I'll put one on it. I just wanted to confirm there isn't anything wrong with the charging system before I put a new battery on it. I'm guessing there is a switch inside the interlock module that kills the engine if the battery voltage drops below a certain threshold, irregardless of the charging system.

 

Both fuses are good and I have continuity between the center terminal on the regulator and the positive battery cable.

It needs a battery regardless, so I'll put one on it. I just wanted to confirm there isn't anything wrong with the charging system before I put a new battery on it. I'm guessing there is a switch inside the interlock module that kills the engine if the battery voltage drops below a certain threshold, irregardless of the charging system.

If your charging system was up to par how would it know if your battery is in place or not? Electricity isn't discriminant.

 

Electricity isn't discriminant.

doesn't discriminate

You did have the engine at WOT when you disconnected the cables?

 

If your charging system was up to par how would it know if your battery is in place or not? Electricity isn't discriminant.

That's what I'm wandering! That's why I came here and asked the question because it seems to me like in a simple system such as the one on this machine, the charging system should be able to support the engine electrical demands perfectly fine without a battery. And I wouldn't think it would be complicated by something in the circuitry that monitors battery voltage, but I'm not certain of that. I didn't want to put a new battery on it only for it to be discharged by a problem in the charging system. I'm sure it work great with a new battery but the question is for how long.

You did have the engine at WOT when you disconnected the cables?

No I didn't. Interesting observation though. Perhaps the charging system can not support it on it's own at idle but could at WOT. I'll check that. Thanks,

 

After doing a little digging, it seems my engine has a DSAI ignition and it DOES require 12v battery voltage. It also seems Kohler has decided that simple is better and has discontinued the DSAI coils and gone back to the old style. So that answers my question. It's a wander I didn't fry the DSAI coils playing with it, as I probably disconnected the jumper cables, while it was running, a dozen times. When they do go, I'll convert it back to the old style that has become the new standard.

 

After doing a little digging, it seems my engine has a DSAI ignition and it DOES require 12v battery voltage. It also seems Kohler has decided that simple is better and has discontinued the DSAI coils and gone back to the old style. So that answers my question. It's a wander I didn't fry the DSAI coils playing with it, as I probably disconnected the jumper cables, while it was running, a dozen times. When they do go, I'll convert it back to the old style that has become the new standard.

No offense, but I think you're wrong. How would it know it doesn't have a battery, if it's already running, and the regulator is supplying 13+ volts back to the battery already. The only way it would know is if the voltage drops. Therefore, the engine would be consuming more power than the charging system is producing. The battery is just being used as a big capacitor once the engine is running. The reason some very smart vehicles quit is because the ECM regulates the alternator. Smaller engines in jet skis, motorcycles, etc quit because they don't produce very much voltage if any below a certain RPM thus inhibits the flow of current through the diode. I think your machine is seeing this drop thus shutting off ignition wise. If it was cutting fuel it would sputter out and die over a longer period of time than an ignition cut out.

 

^ the voltage drop is exactly the problem. Any engine is going to shut off on a large voltage drop
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Well I don't know but I have another piece of equipment with a CH730 on it, I checked it today and it does the exact same thing. It has a hot Optima battery on it and as soon as I pull one of the battery cables off of it, it dies immediately. Perhaps the charging systems on these engines simply aren't designed to support engine's electrical demands on there own.

I also tried it with machines at WOT throttle and they die immediately when the battery is disconnected.

 

Well I don't know but I have another piece of equipment with a CH730 on it, I checked it today and it does the exact same thing. It has a hot Optima battery on it and as soon as I pull one of the battery cables off of it, it dies immediately. Perhaps the charging systems on these engines simply aren't designed to support engine's electrical demands on there own.

I also tried it with machines at WOT throttle and they die immediately when the battery is disconnected.

On a charging system, you need battery voltage on the B+ terminal on the regulator to produce charging voltage. Without battery voltage applied, the regulator will not produce dc voltage. You will produce ac voltage from the stator but it will not be rectified without 12v at the B+ terminal. The fuel solenoid would drop out and the engine would stall.

 

On a charging system, you need battery voltage on the B+ terminal on the regulator to produce charging voltage. Without battery voltage applied, the regulator will not produce dc voltage. You will produce ac voltage from the stator but it will not be rectified without 12v at the B+ terminal. The fuel solenoid would drop out and the engine would stall.

Well there you go then. Thanks. My little 6hp kohler command has both electric start and pull start. It doesn't require a battery. But it also doesn't have a voltage regulator.
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On a charging system, you need battery voltage on the B+ terminal on the regulator to produce charging voltage. Without battery voltage applied, the regulator will not produce dc voltage. You will produce ac voltage from the stator but it will not be rectified without 12v at the B+ terminal. The fuel solenoid would drop out and the engine would stall.

Wrong!
On some charging systems the regulator does indeed need 12v applied.
Not all do! Think about some of the recoil only engines that power some of the smaller walk behind mowers. Some of em have an electric clutch and no battery, correct?

 

BigFish, but would you agree that in this case, the reson for the mower shutting down is the fact that there was no battery voltage to the B+ terminal of the regulator? I have never seen the setup that you are referring to without a regulator. How does the ac voltage from the stator become dc for the clutch? Do they use a diode which is a cheap regulator since the clutch is the only load?

 

BigFish, but would you agree that in this case, the reson for the mower shutting down is the fact that there was no battery voltage to the B+ terminal of the regulator? I have never seen the setup that you are referring to without a regulator. How does the ac voltage from the stator become dc for the clutch? Do they use a diode which is a cheap regulator since the clutch is the only load?

No, that's not the case at all. His particular Kohler rect/regulator doesn't require 12V to get motivated.

I didn't say the no battery units didn't have a regulator. Most all use a rectifier/regulator to convert the AC to DC.
Most diode only systems offer no current-voltage regulation. (Think B&S powered lawn tractors etc )

 

No, that's not the case at all. His particular Kohler rect/regulator doesn't require 12V to get motivated.

I didn't say the no battery units didn't have a regulator. Most all use a rectifier/regulator to convert the AC to DC.
Most diode only systems offer no current-voltage regulation. (Think B&S powered lawn tractors etc )

BigFish, we have Walkers with Kohler regulators and on several machines, high resistance on the B+ wire connector between the engine harness and machine harness has caused the mowers to shut down from lack of battery voltage which in turn caused the battery to go dead. If the OP has a different setup, then why would his machine be shutting down once the battery was disconnected? I am looking to learn from this forum as well as others as experienced as you so can you please enlighten me?

 

Look, read posts 4, 16, 19. Youll see the regulator is not the issue here !
Kohler SAM and DSAI ign systems/modules require apx. 12v to function. They usually get this 12V from the machine wiring, not the engine wiring. If the battery is not supplying 12V for whatever reason, the motor dies.
The regulator FEEDS the battery and the bat. feeds the rest of the system. Again, not all systems work like this, some regulators DO have a sensing circuit that needs 12V into it.
As for yer walkers, they died cause the battery wasn't getting charged due to the poor reg. connection.
Kohler manuals are a free download. If ya don't have any actual experience, then get a manual or two and STUDY.

Any questions, call me in the morning! I'm outtahere.
( almost gametime)