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Old 03-21-2012, 10:59 AM   #1
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Load Testing Batteries - Question

Do the house batteries need to be disconnected from house wiring before load testing.

Since I am load testing the batteries in the golf cart, I thought I would load test the coach house batteries to see what their condition is.


I have searched the forum for this answer but have not found the specific answer.
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Old 03-21-2012, 11:02 AM   #2
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I have always disconnected the battereis before load t4esting. That way I know I won't damage anything. I don't know if you have to disconnect, but I think its better to be safe rather than sorry.

Jim
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Old 03-21-2012, 11:14 AM   #3
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Each battery needs to be disconnected and then load tested. A note of voltage drop for
each taken so you can see if they are equal or you have a weak battery in the system.
Remember one weak battery makes the whole system weak.

Art
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Old 03-21-2012, 11:46 AM   #4
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Quote:
Originally Posted by jlfbatonrg View Post
I have always disconnected the battereis before load t4esting. That way I know I won't damage anything. I don't know if you have to disconnect, but I think its better to be safe rather than sorry. Jim
I agree that it would be better to disconnect the positive and negative terminals; it's just that it is not easy to reach the back negative post. I do have a disconnect switch, however, I don't know what all is actually disconnected... ie: inverter. I should research that for future reference.

Quote:
Originally Posted by wb7auk View Post
Each battery needs to be disconnected and then load tested. A note of voltage drop for each taken so you can see if they are equal or you have a weak battery in the system. Remember one weak battery makes the whole system weak.
Art
When I have had the golf cart batteries load tested they have not disconnected any of the terminals. They have just checked from each battery's pos to negative terminals for each battery. So I would think that would check only the battery that the load tester is connected to (???).

Yes, I am aware that a bad battery will draw down the rest. Makes it expensive to change golf cart batteries...
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Old 03-21-2012, 11:57 AM   #5
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You can load test series connect batteries one battery at a time but parallel wired batteries can not. Most RV systems use a combination of series and parallel batteries
the reason why either the positive or neg post have to be disconnected.

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Old 03-21-2012, 12:45 PM   #6
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The question is about the goal of the 'load test' -- Properly done, this is a destructive test. See batteryuniversity.com (Cadex) to learn about impedance testing as a more modern means of determining battery state of health.

In the RV situation, the need for such testing is questionable as the duty cycle is usually quite long and the gradual reduction in battery capability with age will be usually be noticed in small gradients.

re: "Yes, I am aware that a bad battery will draw down the rest." -- not necessarily so unless you have a traumatic battery failure like a shorted cell (odds are poor for this). Consider the implications of the fact that both smaller and old batteries exhibit the same terminal voltage as new ones for any particular state of charge. Yes, the healthier or bigger or newer battery will assume a proportionately larger share of the load and charge but that doesn't do much more than degrade the battery life a bit faster (unless you go overboard and extreme).
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Old 03-21-2012, 03:29 PM   #7
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Quote:
Originally Posted by Romeo View Post
Do the house batteries need to be disconnected from house wiring before load testing.
Alot depends on your battery control system and hookup.. However that said MINE do, yours, I don't know.

Always best to do that kind of test under "Bench like" conditions (meaning disconnect first.. By removing the NEGATIVE lead from the battery under test)
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Old 03-21-2012, 06:00 PM   #8
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Romeo the only reason for disconnection the neg lead first is to make sure you do not
cause a direct short across the battery if you slip with your tools in doing the positive
first no other reason. You said it was almost impossible to do the negative the reason
I said either one just so one is disconnected.

Art
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Old 03-21-2012, 06:31 PM   #9
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how is a load test destructive? 100-150 amps for 10 seconds should not hurt a battery. what is the highest short-term load you should put on a deep-discharge battery?
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Old 03-21-2012, 10:36 PM   #10
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Quote:
Originally Posted by wb7auk View Post
You can load test series connect batteries one battery at a time but parallel wired batteries can not. Most RV systems use a combination of series and parallel batteries
the reason why either the positive or neg post have to be disconnected.
Art
I guess I would have to diagram a series and parallel setup to try to figure why one would have to disconnect one and not the other to load test, but that makes sense that parallel would be different. My house batteries are series-parallel... I have 4 six volt house batteries to provide the required 12vdc house power.

(I keep falling asleep... taxing day... will have to continue later.)
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Old 03-21-2012, 11:29 PM   #11
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Battery Load Testing Procedure

Well if you really want to know the correct procedure to use to load test a battery, I have listed the procedure I taught for over 20 years.

When load testing a battery. (ALWAYS REMOVE THE BATTERY CABLES) Keep in mind what you are testing for. You are testing for a weak battery and not bad cables. Battery cables with only .01 Ohm of resistance between the post and the clamp will make an otherwise ‘good battery’ test BAD. You can do a voltage drop test on cable to battery post connections. But that is another test procedure.

Now, you can and I have, tested a battery through the battery cable connections, as long as you understand that IF you get a bad reading, you need to take the next step of removing the cables and retest, to determine if it is the battery or the connections that are bad. I cannot recommend this test procedure because over 75% of the time I have had to remove the cables to get a good dependable test.

Load testing battery procedure:
Target test current will be ˝ the CCA (Cold Cranking Amps) for 10 seconds.
Voltage reading at ˝ CCA:
12 Volt battery should be at least 9 volts.
6 Volt battery should be at least 4.5 volts.
When load testing a new battery I have constantly seen 9.8 to 10.5 volts. (I use a digital voltmeter (DVM) for voltage readings)

Testing Example:
Testing a Deep Cycle 6 Volt 200 CCA battery;
NOW put on safety glasses, or better yet liquid proof goggles. You are testing a vessel full of acid. Check and double check your connections and procedure. You are working on a battery that is capable of burning a poorly placed 1/2 inch wrench in two. I have seen batteries explode during load test. Explosions can be reduced to less than a 1% chance if all the battery cells are full of electrolyte.
Make sure all cells are filled with electrolyte to the proper level. Add distilled water if necessary. (NOT BOTTLED WATER too many chemicals still in bottled water)

Make sure the battery caps are back ON! This is your best protection from sparks causing an explosion.
So, . . . PUT THE CAPS ON.
Carefully remove all the battery cables, starting with all negative cable connections.

Make sure to install the tester cables to battery posts clean and tight.
With a DVM also connected to the battery posts, increase the load until 100 amps show on the ammeter. Volt meter should stay above 4.5 volts for at least 10 seconds.

Testing Example: (with cables connected and .01 Ohm resistance on one cable)
The load tester and DVM cables are clamped to the battery cable clamps and not to the battery posts.
At a 100 amp draw a poor cable connection with .01 ohms will lose 1 volt at this connection. (.01 ohm is not even measurable with a digital ohm meter) {well my DVM will only measure down to .5 Ohms} Using the example battery when fully charged the battery should be at about 4.5 volt with a 100 amp draw. Subtract the 1 volt loss due to the bad cable connection and the volt meter will show only 3.5 volts on a battery in top condition. Now is the battery bad or do we have a bad connection? Take the cables off and retest to determine battery condition.

Testers:
I have attached two pictures of load testers. Pulled these pictures off Amazon just as examples. The type I use and recommend would be the red one with adjustable load. The red tester has a built in voltmeter but I do not rely on them. I'm stuck on using my DVM. When working with 100 amps or more an analog gauge is accurate enough. The black tester has a fixed resistance of 100 Ohms so it is only really accurate on a 200 CCA battery. It will give you an idea of the battery condition, and on this thing you might as well use the built in volt meter because it is as accurate (not very accurate) as this entire tool.
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Old 03-22-2012, 01:12 PM   #12
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Quote:
Originally Posted by RinkersRanch View Post
...if you really want to know the correct procedure to use to load test a battery, I have listed the procedure... .
Thank you for that excellent information.

However, I'm not sure it clears up the question of testing with the cables attached if one attaches to the battery posts and not the battery cables. So, if one has six golf cart batteries connected in series, doesn't a connection on ONE battery's neg and pos terminal provide a good load test?

This question should not be confused with load testing of a motorhome's serial-parallel battery bank, which is a different subject (as discussed above).
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Old 03-22-2012, 06:35 PM   #13
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Ah, Ron, I think you have a point. You caught a difference in testing heavy equipment batteries, (my field of expertise), and RV batteries. Heavy equipment batteries do not have auxiliary posts. OOPS!

Now, If I read between the lines just a little you have open auxiliary post you could use to connect your test equipment. (if I'm off base please let me know)
In answer to the question of load testing a battery connected, it will not hurt anything. BUT, . . you should make sure all components are turned off, or use the battery isolator switch to turn all the batteries off. Then testing on alternate open posts will give a good indication of battery condition. The main reason for disconnecting is, if a component is operating it will alter your battery test results. (add a current load not measured with the tester ammeter), To accurate test results, you need to know the exact current draw and the resulting voltage. All the component sees is the battery voltage dropping. The same thing happens when the battery just drains down when in use. If a component will be harmed by low voltage, (like the refrigerator), that component will either shut down or sound an alarm. But your best action is to make sure everything is off or disconnected. I hope this helps answer your question and thanks for the question.
I needed to remember you are asking about RV batteries and not the stuff I use to work on.
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