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Re: (ET) E-15 not getting out of first speed
Hm, ok, I'll first try to measure the voltage of the pack under load. I
measured each battery individually yesterday (with no load, and a few days
since any charging had been done) and they all measured 6.22 to 6.24
volts, which is where they should be. Measuring under load is a little
more difficult.... I could bypass the seat switch temporarily I suppose.
That would make it easy to measure the pack while the blades are going.
I don't suppose there's a known scale for the "fuel gauge", to know
what the voltage is if for example the gauge is right between green and
yellow?
Thanks,
Mike
________________________________
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
________________________________
________________________________________
From: David Roden <etpost drmm net>
Sent: Wednesday, May 17, 2017 1:03 AM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) E-15 not getting out of first speed
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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