Update on this. I charged the batteries for a nice long time, last doing some charging yesterday. This afternoon I took it out to mow - and right away couldn't get out of first speed. I thought to myself "WTF self? The batteries are fully charged - I thought this was a low voltage issue". I measured the pack voltage while the mower deck was on (temporarily bypassed the seat safety switch) and it was around 35.6 Volts, if I remember correctly. That seemed fine considering the three motors do draw a lot of current. I also measured the voltage at the control fuse to see if there might be any substantial voltage drop across any unexpected resistance before that point, and got the same voltage reading.
So I decided to keep mowing, chugging along super slow, for about 20-30 minutes. Then, all of a sudden, it went up into higher speeds. Woohoo! But WTF? I kept mowing for probably 70-90 more minutes, zipping around with the tractor working perfectly.
This behavior seems like more of a loose connection kind of thing to me. If it was a problem due to low voltage (from bad batteries or unexpected voltage drop somewhere in the circuit), I wouldn't expect that to just all of a sudden disappear. Of course, it could be a loose connection causing an unexpected voltage drop....
Any thoughts on where a loose connection might be that would cause this behavior? For the first 20-30 minutes, when it wouldn't get out of first speed while in gear, it would still get out of first speed while in neutral, spinning the motor up nice and fast. I've checked the connections at the solenoids and the main power disconnect switch. The connections are solid, although at the disconnect there are some burn marks at the fusible link - but yesterday I had the vague recollection of accidentally shorting a wire there a few years ago, causing an arc that may have caused those burn marks. At least I think I remember that.... two little kids and lack of sleep is making my memory fuzzy).
The good news is the batteries seem to be fine - I had no trouble mowing the entire yard (and the portion I was mowing initially was very long since I didn't mow it last week, since the slow-motion effect kicked in after mowing for an hour or so).
Thoughts?
Thanks,
Mike
________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________
________________________________________
From: john j casey <
jjcrmc verizon net>
Sent: Wednesday, May 17, 2017 11:52 AM
To:
noaddress drmm netCc:
elec-trak cosmos phy tufts eduSubject: Re: (ET) E-15 not getting out of first speed
Would a specific gravity test be in order?
Cheers, jack
On May 17, 2017, at 1:03 AM, David Roden wrote:
On 17 May 2017 at 0:35, Briggs, Michael wrote:
I'm wondering if I'm just not charging long enough. I'm using a Landis
charge controller.
I would definitely try bypassing it. That said, if it's been undercharging
the battery for some months or years, the damage to the battery (hard or
permanent sulfation) is probably long since done.
A sulfated battery will have a lower on-charge maximum voltage, lower
operating voltage, and reduced capacity. These phenomena aren't reversible
in any meaningful way; the damage is permanent.
I already suggested measuring your batteries' voltage under load (while
driving the tractor and perhaps mowing). I don't see any other way you can
determine whether they can maintain enough voltage to run the tractor
properly without connecting a voltmeter to them and reading it under load.
Sorry, but "they can hold a charge well enough to mow for a while" doesn't
really tell us anything of value here.
As for measuring their capacity, the easiest and cheapest (if approximate)
way I've found requires a 12v inverter, preferably with a capacity of at
least 1000 Watts; an AC powered analog clock with hands (check garage sales
and thrift stores); and a 120v load of some kind.
The ideal load will put a 75 amp load on the battery, because then you can
compare the battery's actual measured capacity to its factory reserve
capacity specification. For a golf car battery, reserve capacity is
normally stated in minutes of operation at a constant 75 amps until the
battery falls to 5.25v under load.
Most cheap inverters are around 70-85% efficient when running at around 2/3
load. Let's take 80% as a reasonable approximation. If you have a really
good inverter with higher efficiency, just plug that value into the math
that follows.
This is not lab equipment and the actual current and voltage will vary over
the test, but remember, I said this is an approximation! At an average of
12v, an average 75 amp avg load will be an average 900 watts from the
battery. Allow for 80% efficiency and you get 0.8 * 900 == 720 watts of AC
load to put on the inverter output. This can be approximated pretty well
with three 250 Watt incandescent light bulbs.
If all you have at hand is a small (< 1000W) inverter, you can still do this
measurement, but then you have to convert to amp-hours and adjust for
Peukert capacity. It's just a little more time and a little more math.
Connect the inverter to a pair of charged 6v batteries in series. Set the
clock to 12:00:00 and plug it into the inverter, along with the lights. Let
'er rip.
When the batteries are effectively flat (around 10.5 volts under load), your
inverter should automatically shut down. You may have to keep an eye on it,
though, because some inverters will start up again when the battery voltage
rises after a rest, throwing off the test.
When the lights go off and the clock stops, read the hours and minutes of
reserve capacity from the clock. Assuming you used 750W of lights, convert
to minutes and compare to the batteries' factory specification. Typical
golf car batteries' RCs are 105 to 125 minutes. A battery is considered
spent when its capacity is below 80% of specification.
David Roden - Akron, Ohio, USA
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