Battery Charger Question

[rgranger]

Hey All

I have a question about battery chargers. I was poking around the boat yesterday with my volt meter (multimeter) ... testing resistance in some old wire runs etc. And I noticed something odd (seems odd to me) on my battery charger. If I disconnect the leads from the charger to the battery and take a voltage across the charger leads... I only get about 3V.

That does not seem to make sense to me. If my battery is charged up to 13V, then I assumed I should get 13V off of the charger. Is the charger sensing the resistance in my multimeter and then scaling down the voltage? And if so, why 3V? Or is it time to get a new charger?

The battery is kind of new so maybe the 13V is not from my charger but just the battery?

I don't get it.

Anyone with more knowledge want to pipe in?

 

[JohnShannon]

You might want to share info about what type of charger.
But today electronics are super flexible. Your charger could have a battery under voltage lockout, that won't allow the battery to be charged if the voltage is too low.

First order you are correct you should see either CC (rated current) or CV rated voltage (13.8 or so) on the output of the charger.

 

[rgranger]

You might want to share info about what type of charger.
But today electronics are super flexible. Your charger could have a battery under voltage lockout, that won't allow the battery to be charged if the voltage is too low.

First order you are correct you should see either CC (rated current) or CV rated voltage (13.8 or so) on the output of the charger.

It is this one...

 

[Chief RA]

Your battery charger does not recognize your meter as a proper load. These suckers are smart and won't really produce a full voltage output until hooked up to a proper load such as your battery. Your readings can be further affected by what type battery position it is set on. Some will put out 13v if you select the correct output position. (labeling varies by manufacturers so just pop to each setting and see if you can get a 13v reading)

Chief

 

[Anonymous 121765]

RG,

I have the same charger. I believe when first charging, for 5 minutes it's giving a full 13+ volt charge. The sensors then drop the voltage down to a trickle charge. This is what I see on my boat.

One thing I do have, is a cheap house plugin timer. I set it to run for ten minutes a day. I don't have any systems running when not at the boat, except my bilge pump. I see some of my pals that leave them on all the time have shorter battery life than mine, especially if you have flooded/not sealed ones. It always seems the acid levels evaporate more. A few friends, not running systems have gone to the house timers. You don't want to cook your batteries.

CR

 

[Anonymous 121765]

RG,

I guess I should add, that if down on the boat running the radio etc. When leaving, I adjust the timer somewhat, or wait abit for the green light to show.

CR

 

[rgranger]

RG,

I have the same charger. I believe when first charging, for 5 minutes it's giving a full 13+ volt charge. The sensors then drop the voltage down to a trickle charge. This is what I see on my boat.
CR

Hey CR....

Are you sure that is what you are seeing. It would make sense to see your current drop but not your voltage. Voltage is analogous to pressure in a water pipe. If you battery is at 13.5V and your charger is at 3V, then the electrons will pass back to your charger. I'm guessing the voltage is high (more than 14V) initially to push more electricity into the battery and as your battery approaches full charge a trickle state someplace near 14V-ish volts is achieved to keep the battery topped off.

I'm guessing Chief had it right and the charger recognized my multimeter as a short in the system instead of a load.

Anyway, a 3V trickle state would not keep your batteries topped off.

 

[LloydB]

I suspect you are measuring the test voltage the charger puts on the charging conductors before it will allow full current and voltage levels to be applied. similar to the dc voltage a ohm meter uses to measure resistance, so too much resistance then no charging or too little and no charging. it would be interesting to know if you would get a +3VDC reading when you reverse the test leads when testing the open circuit voltage of the charger.

 

[centerline]

chief has it right.... its the SMART in the charger that shuts it down when there is no place for the voltage to go.

almost every modern charger for consumer use wont have any output until it senses a proper load....
even if the batterys are dead dead, the charger wont see it as a proper load so it wont come on to charge them up... the charger doesnt know if the batteries are faulty, disconnected or otherwise grounded out. so it will not turn on and self destruct or cause a fire, which would basically accomplish the same thing...

so when it is disconnected and it cant sense a good circuit, it wont show any output...cuz it wont have any.
and some chargers will shut down as soon as it senses something wrong, like a faulty battery, rather than cooking itself.
I am surprised you can see even three volts, although a charger with a float mode may have a constant output, depending on the sensitivity its circuitry.

 

[rgranger]

... it would be interesting to know if you would get a +3VDC reading when you reverse the test leads when testing the open circuit voltage of the charger.

Yes I did that... I could get either +3V or -3V depending on how I hooked up my voltmeter. But the battery to which the charger was connected read 13.3 after I disconnected the charger leads from the battery. What you are saying about the 3V being a "test" voltage from the charger makes a lot of sense to me.

So I guess it is working as it should.

Thanks everyone for your time and input. I always feel smarter after reading this forum.

 

[Anonymous 121765]

RG,

I do not get that deep into batteries & charging man. What concerns me the most, is charging, battery life & usage. I've have used what works best for me this past 15 years. If you still have battery questions, read Main's two posts, who knows where this can lead in thinking. Main also included links for you to use for confirmation, to help you make the best choices and/or decisions.

What MainSail posted is solid info. I thought his take was most informative, up-to-date & in-depth on what the differences are between battery types & uses. Alot of the other postings I felt, were more from a personal preference, rather than backed up by science.

I have a simple 2-bank battery system G27, AGM deep cycles). I do not mix size & type of batteries. I would not use one deep cycle & a starting battery. Nor, would I mix a wet-cell with AGM's or gel types.

What I do now know, is that having the proper batteries & charger, your batteries should have a longer life-span & contain the reserve power to start the iron jib when necessary. This, after a full day drain on your house battery. If this then drags down your house battery, how do you know what the drain from your dedicated battery to he house battery is, devoid of an isolator. Will your engine then start, I cannot say. Look up dual battery equalization issues.

Thus, a hidden power drain could result from the dedicated starting battery power leaking to the weakened house battery that's draining all day long. If not having an bank isolator for protection, I do hope it will start. Again, I can say that both of my batteries last 5 to 7 years on average before a changeout is needed; I can only attest to what has worked for me, and I feel Main has backed this up in his informative posts. It's his business to know.

On the other hand, I look at it this way, if what you are doing works fine for you, then this probably is a non-issue. There then comes into play different parameters for different systems incl., batteries & the like. Having questions, re-read Main's posts again .

I cruise anywhere from a weekend thru a two months on average. I have a simple two bank system & use a simple procedure that insures me power day in-day out. If interested, let me know.

CR