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Old 12-26-2014, 01:10 AM   #21
kpauley
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Default Re: Point me in the right direction for troubleshooting

Be good to have more insight into what you are saying and thinking? I'm not trying to rush out and buy a new motor of course. Would like to understand what the numbers I do have tell so far, if anything.
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Old 12-26-2014, 11:42 AM   #22
JohnnieB
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Default Re: Point me in the right direction for troubleshooting

Quote:
Originally Posted by kpauley View Post
Be good to have more insight into what you are saying and thinking? I'm not trying to rush out and buy a new motor of course. Would like to understand what the numbers I do have tell so far, if anything.
There are three sets of battery voltages used for troubleshooting.
1. At-Rest: When a lead-acid battery is charged, the electrochemical voltage potential is higher at the surface where the sulfuric acid of the electrolyte and the lead and lead dioxide of the plates meet than it is throughout the electrolyte and plates. The opposite is true when a lead-acid battery is discharged.

It takes time for the battery chemistry to reach an equilibrium throughout the cell and reflect a reasonably accurate State of Charge.

After charging, this takes about 12 hours. Voltage measurements taken sooner will be artificially high.

After discharging, this takes about an hour. Voltage measurements taken sooner will be artificially low. (Most of the voltage recover occurs in the first minutes, so for troubleshooting purposes, half an hour will suffice and for a quick check to see when it is time to head towards the charger, 15 minutes is typically enough.)

2. On-Charge: While a charging current is passing through the cells. It starts at whatever the voltage is when the charger is connected and climbs until the charger shuts off, or the cells reach their maximum charge.

Used to analyze battery health and charger performance.

3. Under-Load: While the batteries are being discharged. The more amps drawn from the battery, the lower the voltage drops.

-------------------------

What your voltage measurement tell me:

39.1V = Voltage fairly soon after the charger turned off (not sure how long)
Taken too soon to be meaningful.

43.8V = Voltage while charging after a full pack charge (I unplugged after the above measure and plugged back in.
Charger near the typical cut-off voltage.

38.7V = Voltage roughly 12 hours after a pack charge (similar to what was seen the other day)
Higher than 38.2V, but typical for new batteries.

32.9V = Lowest voltage seen while driving chores / hills
Either pulling a lot of amps or batteries with low AH capacity, but not excessively so.
The lowest routine Under-Load voltage ought to stay above 1.75VPC (Volts per Cell), which is 31.5V for a 36V pack (18 cells).
The max loading is 1.5VPC, or 27V for a 36V pack. Going below that can cause irreversible damage to the plates.

36.9V = Voltage after chores were completed.
That says your battery pack had a SoC of 64.5% after chores, but it was actually higher if that voltage reading was taken too soon after cart stopped.

Need to wait at least 15 minutes, 30 minutes preferable.
-----------
I don't know how far the cart traveled, but it did use about 70% of the useable energy in your battery pack (50% SoC is the max recommended discharge and you used ~35% of the available 50%))

New batteries do not reach their rated storage capacity until the are broken in (about 20 charge cycles). Typically batteries only have about 75% of their rated capacity when new.

Cooler weather also reduces a battery's storage capacity.

After your batteries are fully broken in and the weather gets warmer, your batteries won't discharge as much on the same trip.

Hope this helps.
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Old 12-26-2014, 12:14 PM   #23
kpauley
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Default Re: Point me in the right direction for troubleshooting

Thanks, this does help. These are Costco batteries and they are not labeled with their AH capacity. I'll look more closely but I have not seen it.

I can tell you that getting readings is very difficult based on how we use it. I may be able to get individual measurements. I'll probably be able to get it pre and post charge but not during.
But from what I am reading in your description though it doesn't seem like the batteries are showing any really obvious signs of issues and it is making me think this old motor is starting to give up with the load we put on it (lots of hill driving and pulling a trailer). I just can't take it out of service to inspect or rebuild the motor. If I go after the motor I will have a new one on hand to swap in. I just want to try and do what I can to prove it is the motor, as best possible. I'd hate to drop more cash and still not have improvements.

So, what would be the real telling signs that the motor is the issue? Would a failing motor give poor torque output?
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Old 12-26-2014, 12:41 PM   #24
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Default Re: Point me in the right direction for troubleshooting

Measure each six volt battery voltage with a voltmeter capable of reading accurate voltage under different conditions and determining there is no individual battery voltage dropping excessively.
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Old 12-26-2014, 01:55 PM   #25
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Default Re: Point me in the right direction for troubleshooting

Quote:
Originally Posted by kpauley View Post
Thanks, this does help. These are Costco batteries and they are not labeled with their AH capacity. I'll look more closely but I have not seen it.

I can tell you that getting readings is very difficult based on how we use it. I may be able to get individual measurements. I'll probably be able to get it pre and post charge but not during.
But from what I am reading in your description though it doesn't seem like the batteries are showing any really obvious signs of issues and it is making me think this old motor is starting to give up with the load we put on it (lots of hill driving and pulling a trailer). I just can't take it out of service to inspect or rebuild the motor. If I go after the motor I will have a new one on hand to swap in. I just want to try and do what I can to prove it is the motor, as best possible. I'd hate to drop more cash and still not have improvements.

So, what would be the real telling signs that the motor is the issue? Would a failing motor give poor torque output?
You've got new batteries, 2 Ga cables, HD Cam in the F/R and a SPM48500 controller, which comes with a 400A/1000A Super-Duty solenoid if you got it from Scotty. The cart is not lifted, so the tires are 20" or less in height and have a tractor like tread.

The stock motor is only about 2.5HP, but with the amp delivery system you have, it should be darn near lifting the front wheels when towing the manure spreader uphill, so either the motor isn't generating its rated HP or the battery pack isn't supplying the amps needed for it to generate its rated HP.

To check individual battery voltages, you need a voltmeter that resolves voltages down to 0.01V (IE: A fully charged 6V battery should read 6.37V)
Fortunately, many of the inexpensive DVMs sold in blister packages from an auto parts store or discount store will resolve voltages under 10V down to 0.01V.

All six batteries ought to be within about 0.1V, or so, of each other At-Rest, Under-Load and while on charge.
A battery with a bad cell will be about 2v less than the rest and a battery with two bad cells will be about 4V lower.

If any cable, connection or component other then the motor is getting hot, that is a sign of a problem that needs to be fixed. (Energy being converted to heat is energy not being converted to torque by the motor)


If the battery pack checks out good and nothing is getting hot, that effectively eliminates everything except the motor.

-------------
You carry and tow heavy things, so a top speed in the low to mid teens is probably adequate, so a high torque motor would be best.

Perhaps a D&D 170-004-0001 would work out well for your cart. It generates about 8HP at 36V and has about 40% more torque than a stock motor that is in good working condition.

Here are other possibilities: http://www.ddmotorsystems.com/GolfCartMotorPage.php(Scotty is a D&D Dealer.)


If you need, or want, even more torque and some more speed, buy another 6V battery from Costco that is the same as the others and go to a 42V pack.
The seventh battery fits in space under the driver's seat.
Your controller and solenoid will work at 42V, the pre-charge resistor across the solenoid contacts will have to be changed to 470Ω and you'll have to get a 42V charger.

The DPI Accusense charger like I use is the best bang for the buck: http://www.cartsunlimited.net/48v_Battery_Charger.html
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Old 12-26-2014, 02:17 PM   #26
kpauley
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Default Re: Point me in the right direction for troubleshooting

Thanks JohnnieB, your last response is kind of what I'm thinking and you are accurately describing what I have done. I'll find my DVM and if I can't I'll borrow one to get those individual measurements, but I'm really suspecting the motor. I'll be able to check the batteries individually at the different times except for under load as I'm not sure how I'll do that with the way we use it, but hopefully getting them at the other times will be enough to rule them out.

Haven't been feeling anything hot after use either btw.

I've been talking with ScottyB about a new motor already, he was suggesting the D&D 401 motor for my application as torque is really my target here. He said I'll be sacrificing top speed, but I'm guessing it will probably be equal to our better than what we've had with this motor lately, and if not, torque is still the top priority for how we use this.
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Old 12-26-2014, 02:39 PM   #27
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Default Re: Point me in the right direction for troubleshooting

If you cant find your DVM this is what I use.
http://www.mpja.com/Digital-Multimet...fo/19113%20TE/
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Old 12-26-2014, 03:48 PM   #28
JohnnieB
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Default Re: Point me in the right direction for troubleshooting

I made some long test leads for my DVM(s) out of an El-cheapo 9' two wire AC extension cord I picked up for about $2 on sale. Cut the molded ends off, put alligator clips on one end and banana plugs on the other. Now I can attach a meter to a front roof support and monitor any voltage anywhere in or on the cart while driving.

However, some of my meters have Min/Max and Peak hold functions, so I usually just toss the meter in the sweater basket and check it when I stop.

It is best to read the battery voltage down to 1/100 volt, but we are looking for gross errors in increments of about 2.0V, so even a meter that only resolved down to whole volts in the 6V range should identify a battery with a cell dropping under load.

------------------

The before voltage was fine. The after voltage seemed a bit low, but it depends on the how far the cart traveled, how heavily it was loaded and the AH capacity of the batteries at the time. And if you measure the voltage right after the cart stopped, the reading you got was artificially low.

I have 245AH batteries and after a hard run, their voltage will climb about 0.03VPC in the first half hour after the cart stops. That would be about 0.54V for a 36V pack, and that would raise the estimated SoC from 65% up to about 78%.

-----------------

I'm not fimiliar with the D&D 401 motor. Maybe it is another name for the one I suggested. In any case, I'm sure it is a high torque wind.
From the way your cart is being used, you need a motor than has a lot of torque at low RPM.

In general terms Series wound motor are wound three ways. High low end torque, High high end torque (AKA High Speed motors) and someplace between those two extremes.

Stock motors are middle ground motors with some of the low end torque potential sacrificed to obtain more speed (high end torque). Even the factory installed high torque and high speed motors some carts have are middle ground motors that lean more in one direction of performance than the other. In other words, even if you stock motor was in perfect operating condition, it is very likely to be the wrong motor for your application.
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Old 12-26-2014, 06:00 PM   #29
kpauley
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Default Re: Point me in the right direction for troubleshooting

OK, I had a chance to run some data after finding a better DVM.

A little narrative to go with this. My wife had already used the cart this morning, it had received a full charge earlier today, she did not use it that much though (not her normal run of cleanup).

I took three measurements;
The first one, "A" on the table, would be the baseline. This is after she used it this morning as described above, so it had a full charge about 6 hours earlier in the day and she used it to drive it a few hundred yards around the property pulling the trailer. But this is the baseline for the test.

"B" on the table is right after the simulated daily chore run, no time waited for batteries to settle. What I did was drive the cart roughly the route she takes when she does her daily chores. She drives around a couple paddocks, stop and go, to pick up manure. Then, she'll run around the property with the trailer spreading the manure. This is where we get into some minor terrain/hills. During a bit of the spreading portion I do have the pedal all the way to the floor.

"C" on the table is after waiting 30 minutes after I did the simulated chore run.

After I took the measurements I did plug it into charge. I will check the voltage in a few hours in case that would be helpful. I'm hoping that this is the type of data you're looking for and provides some insight.

Now, here's what else I did and measured. While I was driving through the simulated chore run, the lowest voltage I could see on the pack was 31.2V. I also used my phone to track the route and measure the distance. I've attached some screenshots of that to give you some perspective on this run. You'll see that the top speed was 6.2 MPH, average was 2.9 MPH and elevation change up/down was no more than 26'. Now this was a total distance of just under 1/2 mile, so in a couple spots the elevation changes of 26' are over a pretty short distance (you can see the graph of the elevation changes).

Based on what you were telling me before about voltage changes at the battery level, I'm thinking that everything looks OK and the motor is suspect?

Also, my top speed, does that generally seem low with a stock motor? I think I remember checking it on a roughly flat area before and getting around 7-10 MPH or so.
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Old 12-26-2014, 06:04 PM   #30
kpauley
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Default Re: Point me in the right direction for troubleshooting

Oh, and the #401 motor I think is Scotty's part number for the D&D motor. He described it as a 50% increase in torque, I think a 8 HP unit. "D&D 401 - High torque 8 hp". Not sure what motor that maps to directly at D&D.
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