Tools
You will need more than just a voltmeter to understand what
is going on with your vehicle and its battery,
and the system that charges it.
But you don’t need much, and you
don’t need the latest-and-greatest,
most-expensive tools. Figures 1
and 2 show images of the very simple,
and rather inexpensive, tools
that you need.
Figure 1 shows a small,
inexpensive battery charger nominally rated at 6 amps, and it also shows a very simple and
inexpensive battery load tester. Figure
2 shows a small generalized wire brush,
and a battery terminal-type of wire brush, plus a commonly-available chemical that has
proven effective for reducing corrosion on the steel nuts and bolts that secure
your battery clamps.
Figure 1 – Small,
Inexpensive Battery Charger and Load Tester Devices
Figure 2 – Two Styles of Wire Brush, and a Common Chemical That Cleans Corrosion
From Nuts and Bolts
The chemical was intended to clean hard water deposits and
corrosion from household plumbing items.
However, it does serve our
purpose here, which is to clean
corrosion deposits from the nuts and bolts of our battery cable clamps. And it works rather well for that. It is a poisonous chemical, so be sure to take care not to expose
yourself, anyone else, and especially children, to it.
Problems Usually Encountered
What usually draws one’s attention to batteries and
charging systems is a failure to start when you turn the key to “start”. When it works, you never give it a thought. When it doesn’t, you are stumped, unless you have the right tools, and you also know how to use them.
There are two reasons that a battery might not start an
engine: (1) it is discharged, and (2) it
is “bad”. Those two are not the same
thing. Get out your load tester and hook
it up. If the battery tests “weak”, it could be either bad or discharged, you don’t know which (yet). If it tests “good”, your problem lies elsewhere.
You do this initial test by hooking the load tester positive
cable lead to the positive pole on the battery,
and the negative lead to the negative pole. Immediately,
you will see the needle read a voltage.
This is because the load tester is a voltmeter, wired in parallel with a load resistor sized
to draw a large current from the battery.
You have to activate the test switch to hook-in the load resistor, however.
A 12 volt battery ought to read 12.0 to at most 12.6 volts
at no load. A 6-volt battery ought to
read 6.0 to at most 6.3 volts at no load.
An 8-volt battery ought to read from 8.0 to at most 8.4 volts at no load. The usual no load that values I see on otherwise-charged
batteries are about 12.2 volts, 6.1
volts, and 8.2 volts.
If you see a no-load voltage 2 or more volts below what you
should see, you are “done”: you have a bad cell in your battery. Go get a new one. Simple as that.
If you see a voltage that falls in the range of what you
should see, then hit the load test
switch on the load tester, and hold it
there for 5-10 seconds. The voltage will
drop as long as you hold the load switch,
but hopefully it will not drop too far.
The scale on the load tester dial in Figure 3 shows how much voltage
drop you can tolerate. It has “good” and
“weak” ranges marked, for both 6 volt
and 12 volt batteries. The red “replace”
range is also shown. “Weak” means you
replace it very soon. “Replace” means you replace it right now.
That loaded-voltage drop is almost 2 full volts on a 12-volt
battery, about 1 full volt on a 6-volt
battery, and although there is no
indication on the load tester scale shown,
about 1.3 volts on an 8-volt battery.
If your voltage drop is bigger than what you should see, either your battery is discharged, or it is no good. You must now find out which possibility is
true.
Figure 3 – The Scale on the Battery Load Tester
If you have been running the engine within the last few
hours, and you also know your
charging device (usually an alternator these days) is good, then you know your battery should be charged
as much as it can be. If it has failed the load test under these
circumstances, then it has to be
“bad”. Replace it.
Otherwise, drag out
your small battery charger, and put the
suspect battery on “charge” at 3-4+ amps for about half an hour. Put the positive lead of the charger on the
positive pole, and the negative lead on
the negative pole. Be sure the volt
switch is set to the appropriate 6 or 12 volt setting for that battery. Then plug in/turn on your charger (as
applicable). Before you walk away,
look at how much current it initially draws.
If the initial current is near the nominal max for the
charger, you have at least some
confidence the battery might not be totally “bad”. That current should drop a little bit (from
near 6 amps to near 3-4 amps) during your half hour of attempted charge. However,
faster current drops are more likely to indicate that the battery really
is “bad”.
8-volt batteries are a bit odd, and most cheap battery chargers are not set
up for them. Initially, start out using the 6-volt switch
setting, to keep the initial charging
current within the operating range of your charger. It will start out a bit low on current. Later,
when the current has dropped significantly further, go to the 12 volt setting, which will increase the charging
current. As long as it is within an amp
or so of the nominal current rating of the charger, you are OK.
If you have a battery with filler caps, loosen them before charging, so that the produced gases get to leak easily
out of the battery, without pressurizing
the battery. If not, you need to stay at charging currents under
about 3-4 amp, no matter what. You set the battery voltage lower with that
switch, to control that charging current
to tolerable values. That 3-4 amp current
restriction applies to all of the sealed battery types. You risk a battery explosion, if you fail to heed this warning.
If your charging current starts out low (2-3 amps), and the battery either holds that charging current, or increases charging current very slowly , as time goes by, your battery is most likely totally “bad”. That’s not to say you can’t still charge it
up (over several hours) and successfully use it for a little while yet, but its useful life is now quite limited! Start looking for a new one!
Once you have about half an hour of charge, at 3+ amps,
into the battery, try the
load test again. If it
fails, the battery is “bad”, just replace it! If it passes,
you can try to start your engine and go about what you were trying to
do, except that you have to worry
about why your battery was discharged! And it WAS discharged! Now you know that!
Starter motor failures I am not going to cover here, except to say that if you short the big
battery wire to the solenoid start terminal with a screwdriver, and it tries to start, the starter motor is NOT your most
fundamental problem! Bad
connections, or a burnt/broken wire or
bad starter relay (if so equipped, and
most are these days) can be. And if you
have to ask how to do this starter solenoid short test, you need to seek professional help
anyway.
The next most obvious thing to check is the condition of the
cable connections at the battery. If
these are corroded (or loose), it
restricts current from the battery to the starter, and it restricts current to the battery from
whatever charging device the vehicle has.
Enough current restriction, and
you have first have a charging failure,
and then a start failure because of a discharged battery. The corrosion deposits are blue-to-white
crusty-looking crap on the battery cable connections.
Fixing the Problems
Loose connector bolt torque, you can check with a wrench of the right size
for your connections. In a side post
battery with multiple cables to a single connection, this loose connector thing is a very common
problem! Everybody else, not common at all. But worth checking, in any event.
To fix corroded terminal connections, you need to remove the battery cables
(negative first on negative ground systems),
and wire brush them clean. The cylindrical
battery terminal cleaner in Figure 3 gets this stuff off the top-mount battery
posts, and the small wire brush cleans
it off the lead-based top-mounted battery cable clamp assemblies, and also side-mount terminals. It’s slow,
take your time.
It is wise to remove the bolts and nuts from your battery cable
clamps, and submerge them in the CLR concentrate, in a small glass vessel, if possible.
I usually leave them overnight,
and they look pretty good the next day.
Wash them with water before re-installing. Reinstall the positive cable
first, then the negative (except for the
very rare-indeed positive-ground systems).
If your battery and your starter both test good, then cleaning corrosion deposits off the
connections on the battery usually fixes most starting problems. If not,
then you may well have a bad starter relay. These are not all that expensive. Just buy a new one and install it. Most likely,
that will then fix your starting problem. Every vehicle is different in what these look
like, and where they are mounted. Try the internet for images relevant to your
specific vehicle or machine.
About the only other problem I have ever seen is a bad wire
from the key switch or starter relay,
down to the starter solenoid connection on the starter. As these wires age, they can no longer carry the required
current. They get hard and resistive
from overheating, which limits starter
solenoid current, and that causes start
failures. Just replace the bad wire with
a new one that is a bit larger.
Testing the Charging System
On most cars today,
this is an alternator. Some very
old cars, it may be an old-time generator. For most magneto-ignition lawn and garden
equipment and some old farm tractors,
this charger is built into the magneto that drives the ignition. Whatever it is, it has to generate a voltage that is at the
very least 1 volt above, and no more
than 2-something volts above, your basic
battery voltage. 3 is too much.
All you need to do is use your battery load tester
as a voltmeter with the engine running. Make sure that your engine-running voltage is
at least 1.0 and no more than about 2.5 volts,
above your charged battery terminal voltage with the engine
stopped. With an alternator, this set of criteria is true, even at engine idle speed. That is what the upper increments show in
Figure 3 (marked “low”, “OK”, and a “red” range). This particular tool shows only 6 volt and 12
volt ranges. 8-volt is “in-between”, and
about a third of the way up between the 6 and 2 volt ranges. Just read the volts scale.
With a generator or a magneto, the idle speed charging voltage may not be
adequate. Speed the engine up, into the low end of the operating rpm range
(usually around 1500-2000 rpm), to test
that charging voltage increment, if you
have an old-time generator or a magneto system.
If it still fails,
you will need a new alternator, a
rebuilt generator, or a rebuilt magneto, as applicable. The closer this voltage increment is to 2.0-2.5
volts than 1.0 volt (for a 12 volt system),
the more confident you can be in that test result being a “pass” for
your charging device.
That charging voltage increment over battery voltage also
depends upon the basic battery voltage.
At 6 volts, the min to max
increment range is closer to only 1.5 volts.
For an 8 volt system, it falls
between that and the 2 volt range of a 12 volt system, at about 1.7 volts.
Time In Service
This varies strongly with whatever you paid for the
battery. Longer life is more
expensive. It is usually marked
somewhere on the battery what the “guaranteed” life is to be. There is also usually some sort of indication
of when the battery was purchased.
Failing that, I usually use a
paint pen to mark purchase date and expected life on the batteries that I
buy. They very rarely last longer than
the guarantee, these days.
If you are not sure what the load test really reveals, but you are sure the battery has exceeded its
guaranteed life, then the wisest choice
is to presume it has gone “bad” from old age.
Just buy a new one. It is just
not worth the trouble to “coddle” an over-age battery any further than when it
first shows signs of failing.
Exclusions
None of this advice applies to anything but lead-acid
batteries used to start engines.
Batteries that power hand tools,
and batteries used in hybrid vehicle propulsion, are SPECIFICALLY EXCLUDED from this
discussion!
Routine Maintenance
If you have filler caps,
then open them every several months to a year, to check fluid levels in the cells. If they are low, refill them to the mark with clean, pure water.
Use distilled water, if your
local water supply is mineralized. If
your water is “soft”, then tap water will
serve as well as anything.
Otherwise, there is
just not very much to do, except keeping
the corrosion crud off the connections.
Be sure to put an idle battery on charge every so
often, if it sits for months at a time
without any use. They do self-discharge
over time (3-6 months max). Keep the charging current low (under 4
amp). Charge for around 12-24
hours, but no more.
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