Battery Tender Jr. Low Float Voltage (13.10)

[gathermewool]

I got a Jr. on Black Friday for ~ $17, to keep hooked up as a float charger, as well as a test to see if they're even worth it.

I got busy and wasn't able to monitor charge voltage, max voltage, but note that it has been floating at 13.10VDC for the past couple of days.

This is way too low of a float voltage and I'm trying to figure out why they might have chosen this voltage. Any thoughts?
Temp: mid 40's to 50's, no change in voltage.

//

I typically use a DC power supply to charge our batteries weekly or so. I gave away my two smart chargers to those who need them more than me, so this Jr. will be my only "smart" charger...for now.

 

[Baveux]

What would you like to see ? 13.10 is all good as far as I know , Im willing to learn something here

 

[JHZR2]

That is low. Especially if youre seeing the same temperatures that Im seeing in NJ...

Float voltage should be temperature compensated. Is the charger itself being located in a particularly warm space, while the battery is in a particularly cold one?

Are you sure your meter is accurate?

Are you sure all connections are secure?

Could be a defective unit.

Could also be that the unit is rated at some very low power level, the battery has a lot of capacity (or a high resistance short) and is undercharged, and energy is dissipating full bore from the charger. What can happen then is when pushing full current, there's a voltage drop and so the charger is still in charge (vs float mode) and not getting anywhere due to rating...

 

[gathermewool]

Before I started reading on the etherwebs way back when, I always thought that anything > full charge (~12.7 VDC) would keep a battery fully charged; however, sites like batteryuniversity recommend float voltages 13.5-13.6VDC to account for normal battery self-discharge. I feel like I've also seen 13.9VDC listed as an appropriate float voltage somewhere (I can't find it just now).

Other sites show 13.0VDC as an allowable float charge. 13.10VDC makes sense to me.

Why would a trusted site like battery university recommend a much higher 13.5VDC?

The only thing I can think of that 13.5 is high enough to ensure lower cells stay charged, while low enough no to gas higher cells.

 

[Audios]

The Jr. only puts out about .75 amps, so it is possible that the battery is drawing all of the available amperage and causing a voltage drop like JHZ said. What does the battery read when not charging? Is it still relvatively new?

 

[gathermewool]

Originally Posted by Audios
The Jr. only puts out about .75 amps, so it is possible that the battery is drawing all of the available amperage and causing a voltage drop like JHZ said. What does the battery read when not charging? Is it still relvatively new?


Not probable. Sorry, I left out one very important detail!!!

The Jr. indicates a full charge (green, solid LED). I'm sorry I missed and can't tell you what the charging voltage was; however, 750mA on a full battery will most definitely cook it and raise voltages >15VDC (I don't know exactly how high, but I've seen high 15's at less than an amp before).

//

Additional information:

The battery was charged last weekend using my power supply to 100% and only taken on one long drive since -- 34 miles round-trip to fight a traffic ticket, while sick... It sat for only a day or so after this drive before putting it on the Jr.

Power Supply Charging Information:

When fully charged, it reads approx. as follows:

Voltage: 14.43 to 14.44 (50F)
Amps: 0.04-0.05A (40-50 mA)

After the bulk charging phase at a constant current of 1A to a threshold of 14.4 (nominal @ 25C), I switch to constant voltage (14.4 nom.) and wait for the current to drop to nearly nothing - usually takes > 24 hrs. However, the current drops to less than 100 mA far sooner than 24 hrs.

 

[gathermewool]

Another test I want to do (after some shorter-trips and normal driving), is to disconnect the Jr. and hookup my power supply to see what kind of current it draws at 14.44 VDC. I'm hoping it draws almost nothing, though I kind of suspect that the Jr. only completes the bulk-charging phase and then goes straight to float, leaving the battery somewhere between 80-100% full.

If I tried right now, it would like read closer to full, since it hasn't had time nor been driven enough in a manner that would result in a deplete battery.

 

[doitmyself]

The FAQ page of their site says their chargers maintain a float charge of 0.1 - 0.5 VDC above a typical fully charged battery (12.7 - 12.9v???). Again, at the bottom of the FAQ page they state their charges maintain the float at 13.2vdc.

Based on this, I would say that is what their chargers are designed at, and the OP's unit is not defective out of the box. Whether 13.1v is enough is another question to argue.

 

[gathermewool]

Originally Posted by doitmyself
The FAQ page of their site says their chargers maintain a float charge of 0.1 - 0.5 VDC above a typical fully charged battery (12.7 - 12.9v???). Again, at the bottom of the FAQ page they state their charges maintain the float at 13.2vdc.

Based on this, I would say that is what their chargers are designed at, and the OP's unit is not defective out of the box. Whether 13.1v is enough is another question to argue.


I didn't mean to imply that it was faulty. I was just trying to stir up some conversation about why they chose this number, instead of a higher voltage that seems pretty widely standard.

I also read the documentation and know that there will be some variance in such cheap units.

//

I just ran the battery down by disconnecting the Jr. and turning on the headlights for a minute.

Result:

I missed threshold (max) voltage while charging; however, it was slowly rising and noted to be 13.91VDC 10-15 minutes before, during the previous check.

With the green light flashing (>80% charged), it appeared to cycle voltages, as follows for the minute I watched:
14.14 - 14.25 (initial)
14.14 - 14.26
14.14 - 14.27
14.14 - 14.28
14.14 - 14.29
14.14 - 14.30
14.14 - 14.31
14.14 - 14.32 (minute later)

It stays at 14.14 VDC for a couple of seconds before slowly climbing to the higher voltage of the respective cycle, then immediately, quickly lowers back down to 14.14 VDC. Interesting.

I checked back 10 minutes later (just now) and it's full (solid green LED), with voltage 13.31 and slowly lowering.

//

Weight:

Compared to my old BatterMinder 12117, this thing is liiiiiiiiight. I'm tempted to open'er up and see what she's made of. Someone mentioned online that there were some knockoffs being peddled not too long ago, and the way you could tell, was by opening them up and seeing that it was stuffed with cardboard-like material, for some reason...

 

[doitmyself]

Yes, I was replying to someone else's suggestion that maybe your unit was defective. And, I agree that most literature suggests a higher float voltage (13.4-13.7+/-).

On the other hand, another part of their technical literature states this: " In most cases, a 12 volt lead-acid battery, at 100% SOC, will have a rest voltage between 12.8 and 13.1 volts. That means an effective float voltage need only be as high as 12.9 to 13.2 volts. However, most Battery Tender® battery chargers have float voltages between 13.3 and 13.5 volts. "

So their own literature contradicts itself. Not a good thing for those of us who dissect this information, LOL.

 

[gathermewool]

I've never had a used battery with a resting voltage over 12.7X VDC that I recall, especially not hooked up to the vehicle. To me, the float voltage of 13.1 was being controlled (i.e., the Jr. was providing some current, not just sitting in a monitoring state).

It's now floating again, so I'll check it later to see if it levels out at 13.1 again.

 

[redbone3]

Originally Posted by gathermewool
Originally Posted by doitmyself
The FAQ page of their site says their chargers maintain a float charge of 0.1 - 0.5 VDC above a typical fully charged battery (12.7 - 12.9v???). Again, at the bottom of the FAQ page they state their charges maintain the float at 13.2vdc.

Based on this, I would say that is what their chargers are designed at, and the OP's unit is not defective out of the box. Whether 13.1v is enough is another question to argue.


I didn't mean to imply that it was faulty. I was just trying to stir up some conversation about why they chose this number, instead of a higher voltage that seems pretty widely standard.

I also read the documentation and know that there will be some variance in such cheap units.

//

I just ran the battery down by disconnecting the Jr. and turning on the headlights for a minute.

Result:

I missed threshold (max) voltage while charging; however, it was slowly rising and noted to be 13.91VDC 10-15 minutes before, during the previous check.

With the green light flashing (>80% charged), it appeared to cycle voltages, as follows for the minute I watched:
14.14 - 14.25 (initial)
14.14 - 14.26
14.14 - 14.27
14.14 - 14.28
14.14 - 14.29
14.14 - 14.30
14.14 - 14.31
14.14 - 14.32 (minute later)

It stays at 14.14 VDC for a couple of seconds before slowly climbing to the higher voltage of the respective cycle, then immediately, quickly lowers back down to 14.14 VDC. Interesting.

I checked back 10 minutes later (just now) and it's full (solid green LED), with voltage 13.31 and slowly lowering.

//

Weight:

Compared to my old BatterMinder 12117, this thing is liiiiiiiiight. I'm tempted to open'er up and see what she's made of. Someone mentioned online that there were some knockoffs being peddled not too long ago, and the way you could tell, was by opening them up and seeing that it was stuffed with cardboard-like material, for some reason...


This unit probably utilizes a "Switching Power Supply." They are very light and nearly impossible to repair. (They are also very cheap to manufacture).

 

[wag123]

12v lead/acid wet cell batteries should not be float charged above the 13.5v gassing voltage, 13.4v is ideal, 13.1v is low, and if left on a float charger for extended time periods they need to be given a 1-2 hour 15.5v equalizing charge occasionally to prevent acid stratification.

 

[andyd]

Maybe car batteries need more.. When we built a customer's fiber mux rack it was UPS'ed through a battery consisting of 4 12V batteries in series. The regulator pots were set to 13. x4 = 52 Volts My HF cheapy settles down to 13.10 V in the Rat .15 min after disconnect , battery is 12.5 V. I'll check tomorrow and get back to you

 

[JHZR2]

Float should be 2.25-2.3V/cell at 25C. Something like 5mV/degree C/cell, or 30mV/degree C for a 12V battery. Higher in the cold, lower in the hot.

Originally Posted by gathermewool
I've never had a used battery with a resting voltage over 12.7X VDC that I recall, especially not hooked up to the vehicle. To me, the float voltage of 13.1 was being controlled (i.e., the Jr. was providing some current, not just sitting in a monitoring state).

It's now floating again, so I'll check it later to see if it levels out at 13.1 again.


12.6-12.7V Open circuit (fully disconnected and thermally equilibrated) at 100% SOC is about right. VRLA can sometimes read a bit higher.

 

[gathermewool]

Originally Posted by redbone3


This unit probably utilizes a "Switching Power Supply." They are very light and nearly impossible to repair. (They are also very cheap to manufacture).


That's what I was thinking, too. Definitely not state-of-the-art solid state circuitry here! This thing is most definitely a throw-away item, should it fail and not have an obvious repair.

 

[gathermewool]

Originally Posted by wag123
12v lead/acid wet cell batteries should not be float charged above the 13.5v gassing voltage, 13.4v is ideal, 13.1v is low, and if left on a float charger for extended time periods they need to be given a 1-2 hour 15.5v equalizing charge occasionally to prevent acid stratification.


I perform an equalizing charge every few months +/-, after a full charge; however, I'm too chicken to apply such a high voltage for that long. An hour at 15.0 VDC is around what I do, compensated for temperature.

 

[gathermewool]

Originally Posted by andyd
Maybe car batteries need more.. When we built a customer's fiber mux rack it was UPS'ed through a battery consisting of 4 12V batteries in series. The regulator pots were set to 13. x4 = 52 Volts My HF cheapy settles down to 13.10 V in the Rat .15 min after disconnect , battery is 12.5 V. I'll check tomorrow and get back to you


I think there are different charging schemes, based on use; however, I think that doing anything is better than doing nothing.

In other words, performing equalizing charges monthly may cause some extra plate erosion, but it's better than never doing it for a battery that mostly sits at float voltage. Choosing a charging bulk threshold (and constant-voltage) voltage of 14.1 VDC, 14.4VDC or 14.6 VDC (for 12 VDC nom. L-acid) is better than doing nothing for a car that short-trips and never sees extended highway service (i.e, it's better to cause a small amount of damage due to too low of a topping voltage or too high than to allow the battery to normally sit at 50-80% charge 24/7, 365)

 

[gathermewool]

Originally Posted by JHZR2
Float should be 2.25-2.3V/cell at 25C. Something like 5mV/degree C/cell, or 30mV/degree C for a 12V battery. Higher in the cold, lower in the hot.

Originally Posted by gathermewool
I've never had a used battery with a resting voltage over 12.7X VDC that I recall, especially not hooked up to the vehicle. To me, the float voltage of 13.1 was being controlled (i.e., the Jr. was providing some current, not just sitting in a monitoring state).

It's now floating again, so I'll check it later to see if it levels out at 13.1 again.


12.6-12.7V Open circuit (fully disconnected and thermally equilibrated) at 100% SOC is about right. VRLA can sometimes read a bit higher.


I totally meant to say 12.6X VDC, not 12.7X VDC. I saw it after the time-to-edit had expired, so I just let it go. Good catch!!!

When I buy a new batter, I will not take it home if it's not between 12.6 and 12.7 VDC.

Case-in-point: NAPA pulled out a dusty-[censored] battery for me last year that measured 12.4 VDC or there about. They had no problem with me rejecting it and came out with a sparkly-new-looking battery that measured 12.6X VDC! I wonder how long the 1st battery would have lasted. It likely sat its whole life in a temperature-controlled room and never saw a full discharge, but no thanks!

 

[gathermewool]

Float is still 13.10 VDC

Switches quickly and voltage raises momentarily to 13.12 to 13.15 VDC every several seconds