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Schumacher Digital voltmeter battery question

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John Niekamp
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Schumacher Digital voltmeter battery question

Postby John Niekamp » Sat Oct 28, 2006 11:45 pm

I am not sure where to place this topic at so I decided to stick here since it doesn't really pertain to Cubs or does it? It can be used on 6 volts as well.
I purchased this little item to be able to keep a little closer eye on my motorhome's coach battery. It's quick, compact and easy to use.

Since I was trying to charge up a very low coach battery on my Lesharo last year from the engine's charging system, the alternator got very hot and melted the solder in diodes and took out the field, so needless to say I have been really cautious ever since. Even though when I converted the Renault engine/transmission over the GM 3800 I also installed a higher amperage output alternator on the engine in hopes this would help.

The guy who rebuilt my original Renault alternator told me it was probably due to the fact that I was trying to charge a dead or very low deep cycle battery off the engine's charging system and this really overtax the alternator. He suggested that I should check the voltage of the coach battery and use a battery charger to charge the battery overnight first and then use the alternator to maintain that level of charge so the alternator will not become over taxed again. I have a switch on my dash that I can charge the coach battery as needed or when ever I want, but I don't have an ammeter, just a volt meter, so I can't tell how much current is actually doing. Probably if I had an ammeter at the time I would have noticed where it was really sucking up the current, I would have definitely known something was wrong.

I'm guessing with a regular 12 volt car/truck/tractor battery it doesn't cause any harm to the alternator to bring them back up from a discharge state??? I guess it's due to their thinner plates?

On this digital meter, what I DON'T really understand is the letters "SLI" and "VRLA" (right hand columns) stand for and the manual was of no use either. It just said how to hook it up and that was basically that was it. Even Schumacher's web page here at: http://store.schumachermart.com/bt-50.html
says even less than what the so-called manual did.

This is a picture of my meter, can anyone tell me what the "SLI" and "VRLA" represent??? other than they are voltages of some sort.

Thanks for any thoughts,

John

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Jack fowler
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Postby Jack fowler » Sun Oct 29, 2006 7:25 am

Technically, both batteries are the same (deep cycle batteries) (thick plates). SLA- sealed lead acid, VRLA- valve regulated lead acid.

The SLA has a typical capacity range of 0.2Ah to 30Ah and powers personal UPS units, local emergency lighting and wheelchairs.

The VRLA battery is used for large stationary applications for power backup. Car battery jumper, leisure boat trolling battery and R.V. applications.

State of charge in a battery

The charge level depends on the concentration of acid inside the battery. The stronger the concentration of acid in the water, the higher the specific gravity of the solution, and the higher the state of charge.

Uncommon now days....

On batteries with removable caps, state of charge can be checked with a "hydrometer." Some hydrometers have a calibrated float to measure the specific gravity of the acid solution while others simply have a number of colored balls. On the kind with a calibrated float, a hydrometer reading of 1.265 (corrected for temperature) indicates a fully charged battery, 1.230 indicates a 75% charge, 1.200 indicates a 50% charge, 1.170 indicates a 25% charge, and 1.140 or less indicates a discharged battery. On the kind that uses floating balls, the number of balls that float tells you the approximate level of charge. All balls floating would indicate a fully charged battery, no balls floating would indicate a dead or fully discharged battery.

Common now days

Some sealed-top batteries have a built-in hydrometer to indicate charge. The charge indicator only reads one cell, but usually shows the average charge for all battery cells. A green dot means the battery is 75% or more charged and is okay for use or further testing. No dot (a dark indicator) means the battery is low and should be recharged before it is returned to service or tested further. A clear or yellow indicator means the level of electrolyte inside has dropped too low, and the battery should be replaced.

How to check a state of charge

On sealed-top batteries that do not have a built-in charge indicator, the state of charge can be determined by checking the battery's base or open circuit voltage with a digital voltmeter or multimeter. This is done by touching the meter leads to the positive and negative battery terminals while the ignition key is off.

A reading of 12.66 volts indicates a fully charged battery; 12.45 volts is 75% charged, 12.24 volts is 50% charged, and 12.06 volts is 25% charged.

John wrote:

GM 3800 I also installed a higher amperage output alternator on the engine in hopes this would help.


John, give me the specs on that alternator and I’ll tell you how much you can expect out of it.

I would do what the technician said who rebuilt the Renault alternator said; "keep the battery charged with an external charger".

The only alternator I know of at this time that will charge that type of application and not have a large fail rate is an alternator Ford uses on their heavy applications, which is Penntex.( I work on both GM and Ford)( I’m sure there are others)
Last edited by Jack fowler on Mon Oct 30, 2006 10:45 am, edited 1 time in total.

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Postby KYMike » Sun Oct 29, 2006 7:40 am

SLI is Starting, Lighting and Ignition batteries. VRLA are Valve Regulated Lead Acid batteries and I believe they are deep charge batteries. I think the chart represents what the nominal voltage of the battery is when not under load, and the percentage of charge left in it.

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Postby Jack fowler » Sun Oct 29, 2006 10:41 am

Thanks Mike for the correction. I thought I read SLA instead of SLI. :oops: (Two different subjects) Yes you are correct.

What the DVM is showing is the difference of open circuit voltage between a SLI battery and a deep-cycle battery. Because of the structure between the two batteries the voltage between 50-100% is higher on the VRLA battery(50-100% charged)because of the heaver plates.

The scale you see on the Schumacher DVM is the actual state of charge in the battery.(Depending SLI or (VRLA )(deep-cycle battery).

SLI (starting, lighting & ignition)
SLI batteries are commonly used to start and run automobiles, where a very large starting current is needed for a short time. SLI batteries have many very thin plates with a large surface area, designed to be discharged no more than 1 to 5% from full charge. These can be damaged quickly if deep cycled.

Marine / Deep Cycle
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates.
The so-called Marine deep-cycle batteries are actually a "hybrid", fall between the SLI and deep-cycle batteries. These should not be discharged more than 50%. SLI batteries are usually rated at "CCA", or cold cranking amps, or "MCA, Marine cranking amps". Any battery with the capacity shown in "cranking amps" is NOT a deep-cycle battery, and some marine batteries with MCA ratings may be a hybrid (basically a battery with thicker plates than an automotive battery, but thinner than a true VRLA deep-cycle).

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Postby John Niekamp » Sun Oct 29, 2006 10:47 am

Well now why couldn't the manual say it simple like that? I was almost sure that the "LA" on the back of them letters must have meant something lead acid.

The orginal alternator on the Lesharo by Renault was a 90 amp alternator, I always thought it was a little low in output, but since I knew I was going to do the change over I knew there was no need to worry about trying to adapt anything different to it. I just had it rebuilt and sold the engine all as one complete uint with new reuiblt atlernator.

The new engine setup that I used with the 3800 Series II came from a 1999 Buick Lesabre had a 105 amp? I thinking it was, maybe it was a little higher, for it did have a lot of power everything. Anyhow I went and got a new alternator for a a 3.8 liter Cadillac that I am wanting to say was either a 160 or 165 amp. I figured that I would go with an alternator for a car that used the most electric there was.

I know I can see the volt meter drop in voltage on the instrument gauge when I apply the dual battery switch, but then it jumps back up in the correct voltage range in just seconds. (The way this works, there is a soleniod that is connected to the main battery when the switch is in the "dual" postition it makes the connection to the main battery to charge up the coach battery) I transplanted the complete instrument gauge cluster from the 99 Buick Lesabre donor and maybe the volt meter in it may not be as accurate as an indpendant meter would be.

So in short, I should be using the meter readings with the "VRLA" reference scale to check deep cycle coach battery use "SLI" for modern day car/truck/tractor batteries? any guess on to what amount of charge I should consider to be safe to charge the battery from the alternator while going down the road in my little motorhome?

The only batteries that I still have that actually have caps that can be taken off are my 6 volts batteries for the Cubs and Model T's and so forth. I don' t know of they any makers of a "maintenance free" 6 volt battery or not.

Funny thing is if I use the power inverter/charger in the motorhome and leave it plugged in for more than a day or so, it with then overchage the coach battery, just can't seem to win here, :lol: I guess the best thing to do here is get a mainteneace free fully automatic 1 amp. trickle charger and get a quick disconnect switch on the coach battery and let the charger decide when to turn on and off to keep the battery at full charge.


Thanks for the help here Jack and Mike

John Niekamp
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Postby Jack fowler » Sun Oct 29, 2006 11:47 am

I think what you have is a 130 amp.generator (That’s what GM calls alternators). Cadillac doesn’t list a 3.8 engine. Catera had a 3.0 L.

What the problem is how long the Generator can maintain the higher Amp (High charge rate), (Flow of electrons at a high rate) with out burning up. Usually the GM CS type generators don’t do that very well.

Ford uses an alternator on their heaver applications that has an output of 215 amps that will maintain 96% amps. at under hood temperature of about 230 degrees F. continuous operation on gasoline engines.(They run hotter than diesels). Usually about 6 -12 month of operation the alternator will fail. ($300.00 each)

Believe it or not Cadillac now runs coolant through their generators keep them cool.

I know you have some good R.V. Shops in your area. Go in and talk to a Technician and I’m sure he or she will have an answer, hopefully not an expensive one.

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Postby George Willer » Sun Oct 29, 2006 4:42 pm

John,

Did you have as much trouble as I did finding the coach battery in the first place? I never imagined anyone would put the battery in a box and bolt it to the underside of the floor without an access panel. :( I was in my mid 60's when I had to deal with it. A can testify that it is unhandy.
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Postby John Niekamp » Sun Oct 29, 2006 6:14 pm

George Willer wrote:John,

Did you have as much trouble as I did finding the coach battery in the first place? I never imagined anyone would put the battery in a box and bolt it to the underside of the floor without an access panel. :( I was in my mid 60's when I had to deal with it. A can testify that it is unhandy.


NOPE, I didn't have that un-fun pleasure George, what a STUPID idea. I bet that whoever came up with that brain fart!!!! If he ever had to change one I'm guessing he would have mounted it about the same way as mine is mounted. :wink:

What do you want to bet George it was probably the same engineer who decided that an underpowered 4 cylinder engine would be a good idea too?

Winnebago, finally got a little smarter on the last couple years of production of the Lesharo's and they added more room on the front end to where the coach battery could be mounted where it should be. However I think they continued to mount them underneat. It took someone with some common sense to put it up next to the engine battery. My friend who has an 85 Lesharo is doing the same 3800 conversion as I did, but unfortunately he don't have any extra room to mount his coach battery like mine is, so I don't know what he'll come up with on his.


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Here ya go George, I don't know if I showed you mine just before I took the engine out of the Lesharo getting ready for the conversion with the origianl Renault 2.2, even tho I know you had the diesel 2.0 liter.

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1954 Regular F-Cub "PRB" (Puckett's Rust Bucket)
1955 International Cub LoBoy "SQUATTY"
1954 3800 series Chevrolet flat bed grain truck "Ole Ben"
1975 Case 1737 skid-steer


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