G-16? shudders at low rpm when hot

[joesam]

I'm trying to help a friend troubleshoot his (mfr. later '90's) Yamaha (G-16 maybe). Since I have primarily helped people with Club Cars I'm not in familiar territory. It has only one modification from stock - namely the 8:1 gears in the rear axle. Its quite high speed/lo-torque as a result - flat out it goes about 25mph.

Here's the symptom:

When its been run for about 10 minutes - the cart/motor shudders when starting up. If its been running for about an hour, and if you hold the accelerator pedal to creep forward - it shudders continually. If you floor it - it shudders while the rpm builds and eventually the shudder goes away and seems to move smoothly.

The hotter the motor gets, the more the shudder lasts during acceleration. And the power to accelerate while shuddering is weak. From dead cold it seems normal - but within 10 minutes or so, the shuddering starts happening. My assumption is leaning toward a motor issue (armature or brushes etc.) because the hotter the motor, the more the shudder. But I'm not familar with the controller on these carts. Does anyone think this sounds like a controller issue?

BTW - the batteries were new in spring - and all cable connections are tight & clean. The voltage on the battery pack checks out - and it recharges fine.

Thanks

[scottyb]

Check 2 things
When the cart shudders, is the solenoid clicking rapidly?
Put a meter on the battery pack and report the pack voltage when the cart is shuddering.

[joesam]

Oh, hi Scotty. The batteries were the first thing we checked with a DVM - both separately and as a pack. No luck there. Holds voltage decently well during load. Think the lowest we saw on the (2 mos. old) pack was about 46.7 or so (after a round of golf before mild hill testing). It was over a week ago - but I think that's what it was - no eureka moment for me. Individually there was a variance between them - but again, nothing dramatic.

No solenoid noise (thanks for asking)....eerily quiet in fact - even when the pulsing is at its most noticable - when holding the lowest speed possible on a hot motor.

Its not a neck breaking shudder - more like sagging pulsation. Ties exactly to rpm (the slower the revs, the more pronounced the pulse) - to me, I think one of the copper strips on the commutator is burnt or arcing. Hotter motor is worse - cold motor is zero or almost undetectable. Can a commutator do that? I just didn't want to tell him to pull the motor (he's fully capable of that) unless someone who knows Yamaha thinks its the motor and not something else that might be typical of Yamaha.

I'm also wondering if the added load of the gears could have brought on a motor failure prematurely - I've never experienced an actual failing motor before, but there's always a first time!

[cgtech]

If you have 48v you have a g19e. That particular GE motor is not known for its awesome-ness when paired with high speed gears. If you crack the motor loose from the axle, and its bad, you can smell its distinctive odor, smells like money...

[joesam]

Thanks cgtech - yes it must be a G19e - it is 48v. Now that you mention it, I do recall the owner being frequently underwhelmed with the torque available after he had the gears installed (seems to me the word "dog" was used a couple times). I suspect it IS the motor, so I'll have to help my buddy do some research as to the cost of a higher torque replacement (I'm familiar with Club Car motor upgrade options, but a total novice with Yahama - time for a little research).

I'll also have to read up on how best to pull the motor - 'cause I know I'll be helping.

[cgtech]

Motor options are very limited with stock controller, all "sepex" carts need a motor tailored to the stock controller OR an aftermarket controller that can have the motor profile (AKA "field map") changed to suit the motor being used. It is not a case of "any sepex motor will work"!

[joesam]

I'm aware of the correlation between controller and motor (but only as it relates to CC) - but I was hoping there'd be a standard controller-compatible (but slightly higher torque) motor option. Maybe not....as I said - Yamaha's are new to me. I was thinking maybe a 4 ga. cable upgrade with a somewhat better motor would be a good (and affordable) idea; if it were available.

He's not trying to build a stump-puller. Currently his cart has trouble getting up some fairly minor hills without a running start and he figured since the bank account is gonna take a hit - it would be nice to see some improvement.

Given the year of the cart - I don't know how willing he'd be to throw $1,000+ at it. Also - I need to do better (eg. some) research so I can ask rational questions on this forum about his motor options. I promise I won't tell him to buy a 500 amp motor and let him fry his controller!

[joesam]

OK - just did some quick searches - your not kidding - motor options are really limited without a controller upgrade or reprogramming (at the very least). Will his stock controller be reprogrammable or were the mid-to-late 90's stock controllers non-programmable on G19e's?

Guess I'll have him pull the motor and sniff around for the "money smell". There is a decent DC motor rebuilding place here if its not totally fried. It does look like he'll benefit from 4 ga. cables in any case if he wants to just get back on the road.

[cgtech]

His controller "may" be programmable by someone like FSIP, but you cant do it. His stock 300 amp controller & motor is fine with stock 6ga cables, if they are in good condition.

[joesam]

I haven't inspected his cables (but I will). I was hopeful that even if he has a stock motor (replaced or rebuilt), larger 4 ga. cables might supply just a little more "grunt" while going up small inclines (remember he has those long legged gears). Is that just wishful thinking on my part?