6 volt SLA charging question

[degarb]

Radio Shack has a 6 volt 4.5 amp hour for $15 that weighs 1 lb. I figure about equal to 12 AA's (1900 mAh), and size makes it practical for a headlamp with toolbelt power or overcoat pocket

So, I am now wondering what is the most street-practical way to charge it, and its 3 brothers, for daily work use. I have a 12 volt auto battery charger with 2 amp and 6 amp setting; wondering if put two of these 6 volts in series, connected to the 2 amp setting, and use a 3 hour timer?

Or, I could use the 6 volt 6 amp charger, with a 1 hour cutoff. (something like 1.43 time of rated capacity)?

Is my two charging options above possible with those times? (Do you measure charger voltage not under load?) (Doesn't 1 to 3 hours sound a bit too fast? Is so what resistor would I need at what wattage rating?)

 

[degarb]

Re: 6 volt Lead acid charging with auto charger question

One other question: on a 4.5 amp hour battery, if you use 4 amp in a day, is this considered a deep discharge?

Also to get 200 to 300 cycles, do you need a circuit charger or just timer? Also, what is a cycle again? Would 5 days using 2 amps be considered five cycles or only closer to two cycles?

 

[degarb]

Re: 6 volt Lead acid charging with auto charger question

One other question. Has anyone tried running two head in series off a 6 volt sla? (rebel 80 and xr-c is my idea) This look like may be below forward voltage, but I just saw a demo pumkin led light ran off 2 AAA's below the led's forward voltage.

Could run them in parallel, and still have double capacity of 3 AA's, but would rather press for 12 AA 1900 mAh capacity.

 

[Closet_Flashaholic]

Lead acid batteries (sealed or otherwise) do not like to be discharged to less than 50% of capacity, as a rule of thumb. I don't take them much below 60%.

So for your 4.5AH, I would only draw about 2 - 2.25 AH worth of total energy before stopping for a recharge. You can discharge them further (i.e. just once), but they are permanently damaged at that point.

If it's not a gel-cell, then charging at a rate of C/10 is ok. This would be 4.5/10 = 450 milliamps for the bulk charge portion. For gel-cells I keep between C/15 and C/20 so that the electrolyte doesn't bubble (permanent decrease in capacity if this happens). AGM batteries can be charged at much higher rates, but it depends on the specific manufacturer.

 

[degarb]

Thanks. That answers some of the questions.

Just tested the battery with xr-c and xr-e in series. Too dim. But threw in a single AA in series and they lit up nicely, drawing 290 milliamps with no resistor ( 2.3 amphour in 8 hour or 50% or about %66 in 10 hours. Not considering voltage drop of the AA over 8 hours.)

I threw a volt meter on charger and it showed only 6 millivolts. So guessing it needs a load to start pumping voltage. By your post, I assume only way I can test if charging correctly, is put meter in series to test current and beware if over .45 amps.

AGM look like the answer to lions for belt supplied, based of first page of reading.

 

[Turak]

I assume you are talking about the following 6v 4.5A SLA/AGM Battery;

http://www.radioshack.com/product/i...84&cp=&sr=1&kw=6v&origkw=6v&parentPage=search

You can go and look up almost any of the major SLA battery manufacturers and pull the data sheet for their 6V 4.5Ah SLA/AGM battery. They are all very close in respect to charge rates, disharge rates, cycles, etc.

Here is a blurb regarding the recommended charging rates for 6V 4.5Ah SLA/AGM Batteries;

​

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​

​

​

​

Cycle Applications:​

​

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Limit initial current to 1.35A​

Charge until battery voltage (under charge) reaches 4.8 to 5.0 volts at 68°F (20°C). Hold at 4.8 to 5.0 volts until current drops to under 45mA. Battery is fully charged under these conditions, and charger should be disconnected or switched to "float" voltage.​

​

​

"Float" or "Stand-By" Service:​

​

​

Hold battery across constant voltage source of 4.5 to 4.6 volts continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition.
​

Note:

Due to the self-discharge characteristics of this type of battery, it is

​

​

imperative that they be charged within 6 months of storage, otherwise permanent​

loss of capacity might occur as a result of sulfation.


Regarding the number of typical cycles;

100% discharge = about 150-200 cycles
50% discharge = about 350-500 cycles
30% discharge = about 1000+ cycles

​

 

[FredM]

I would much prefer 12 AA's than one SLA.

An eneloop will have over 18500maH at a 3.0amp rate which is much more than the 4.5mah SLA will have.

 

[lctorana]

I would much prefer 12 AA's than one SLA.

An eneloop will have over 18500maH at a 3.0amp rate...

Where can I buy THOSE?

 

[mdocod]

An eneloop will have over 18500maH at a 3.0amp rate which is much more than the 4.5mah SLA will have.

First I'm going to rewrite this as I think you intended....

"An eneloop will have over 1850mAH at a 3.0A rate which is much more than the 4.5AH SLA will have"

Then going to point out, that a headlamp probably won't draw 3 amps from a 6V source. So the SLA in this case should perform reasonably well.. but I doubt it will ever deliver a full 4.5AH.

--------------------------------------

In response to the original questions. The SLA may look good, but it's weak points will start to show up in time. As Turak has pointed out, the cycle life isn't very good on deep discharges. Truth be told, those figures are probably very optimistic anyways. I'm not sure how much capacity you can expect the battery to actually hold after 100 cycles, it may still work, but it won't be a 4.5AH battery anymore.

--------------------

You probably *could* direct drive 2 LEDs in series on the 6V SLA, but it hard to say what kind of results you will get, the only way to find out would be through your own testing, especially since every LED has a different Vf, it's not something that can be answered with any great degree of accuracy in a thread on a forum unless someone else had the exact same LEDs with the same Vf with the same battery in the same state of charge.

If you want to use 2 LEDs in series, you'll be much better off with a higher voltage power source, and a constant current buck regulator. There are plenty of regulation options all over the net for driving LEDs from various power sources. Some are just a few dollars through DX/KD etc, so it's not expensive.

A pack of 8AA eneloops would weight ~0.5lb, have ~9.6V ~1950mAH capacity, and work well with many possible buck drive solutions. It would also likely last several hundred cycles while still maintaining good useful capacity.

A 4x18650 li-ion pack would weigh even less than 8 eneloops, and have about 30% more power stored, but would have more complicated charging requirements.

Eric

 

[degarb]

I assume you are talking about the following 6v 4.5A SLA/AGM Battery;

http://www.radioshack.com/product/i...84&cp=&sr=1&kw=6v&origkw=6v&parentPage=search


Here is a blurb regarding the recommended charging rates for 6V 4.5Ah SLA/AGM Batteries;

​

​

​

​

​

​

Cycle Applications:​

​

​

Limit initial current to 1.35A​

Charge until battery voltage (under charge) reaches 4.8 to 5.0 volts at 68°F (20°C). Hold at 4.8 to 5.0 volts until current drops to under 45mA. Battery is fully charged under these conditions, and charger should be disconnected or switched to "float" voltage.​

​

​

"Float" or "Stand-By" Service:​

​

​

Hold battery across constant voltage source of 4.5 to 4.6 volts continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition.
​

Note:

Due to the self-discharge characteristics of this type of battery, it is

​

​

imperative that they be charged within 6 months of storage, otherwise permanent​

loss of capacity might occur as a result of sulfation.


Regarding the number of typical cycles;

100% discharge = about 150-200 cycles
50% discharge = about 350-500 cycles
30% discharge = about 1000+ cycles

​

This is very exciting. I do see this is an agm http://ebatteriestogo.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=EBTG&Product_Code=D5733-WB
Also, see this battery usually goes for 10 bucksm not the inflated Radio shack price, making it more ideal for a work light, where a small business might run 3 to 8 light for one job. A typical 75% 85% discharge seem more liveable (3.4 to 3.8 amp hour over 10 hours). (I see other sites talking %75 discharge is okay.)



I am not sure I am getting my head around how to charge this battery, properly. Physically, how do I charge this with a multimeter, timer, and available (auto or shack or lowes) charger or power source? And if I need to buy some resistors to limit charge, what is the formula to choose the resistor...?,,, (Say, to drop 4 amps at 6 volt to 1 amp at 6 volt for 3 amp drop, would I need 6x3= 18 ohm, 24 watt resistor? Do they sell them?)

I am wondering, could I use a wall dimmer switch, and measure down to desired amperage? Like, 1.35 amps for first 5 hours, click off via timer, then top off at a lower amperage for some period of time?

 

[degarb]

Looks like pulse charging is only in lab. Not made it to stores yet.

 

[eluminator]

This is the charger I use. I get the cord too for a total of $17.90.
http://www.batterymart.com/p-6v-500ma-sealed-lead-acid-battery-charger-2.html

 

[jerry i h]

Out of curiosity: why use a SLA/AGM battery to power a few LED's? If your requirement is 6v, why not use a 5xD cell rechargeable battery pack. NiCd's will give you 5AH, NiMH yields 10AH. When the batts get weak, take 'em out of the battery pack and stick 'em into a charger. Yes, no?
At work, we have one hydraulic piece of equipment that is powered by a marine, deep-discharge battery, and a forklift powered by what looks like an ordinary car SLA cell. The only difference that I have seen is in how often we have to plug it in overnight to recharge.

 

[poguy]

My $0.02 on SLA's: They can be had really cheap, sometimes free. SLA's are used in many medical devices and must be cycled out when they still have years of service left. I got several 12 volt 2-2.3 ah gel cells this way.
<p>
Keep them charged all the time (they don't like to be stored discharged) and they will last forever. All have 1997-1999 date codes and still work OK for bicycle lights.
<p>
If I had to buy something new it would be NiMh. You can't use an SLA in a wireless TV remote or flashlight...

 

[degarb]

First, 4 Sla's at $10 and two $30 chargers (two 6 volts in series with resistor or dimmer = 12volt). So charging will be cheaper and easier. I think 28 watt hour in battery pack a good target for a duel head led.

Expandable availability on demand, as meed arises.

 

[degarb]

This is the charger I use. I get the cord too for a total of $17.90.
http://www.batterymart.com/p-6v-500ma-sealed-lead-acid-battery-charger-2.html

Thanks, I am open and curious to all users experience with various types of chargers and methods. I would pay more for a pulse charger, if one existed, to extend cycles.

 

[degarb]

Actually, I envision charging 4 6volt sla agms at a time (maybe, with current limiting resistor, as in dimmer switch), using standard 12 volt car charger (two sets of two in parrallel: 2 amp setting or 1 amp per cell). I would monitor current with multimeter, of course.

But, how bad would this be if all cells weren't discharged equally?

Or, could a dimmer switch, modern or old type, be used before or after charger to better control charge? http://home.howstuffworks.com/dimmer-switch.htm/printable
According to this, there would be some interesting things happening if you use a modern dimmer switch (before or after charger). Anyone know what this would be?

 

[degarb]

Tried a dimmer switch with no luck to lower amps pumping into this 6 volt agm from the Shack. (So, going to wire the dimmer into wall. )

I read on http://www.bitwrangler.com/wt/lv-ab-agm.html that agms can take 75% of their rated capacity. I took my car 6 volt 4 amp and was able to recharge the agm from %25 from dead up in a tad under 30 minutes--I had to watch carefully, and didn't feel the battery getting hot. Doing new tests on two head today, and running fine. SO,,,I might just charge two at a time in parallel for one hour, and have option to charge up to eight with this charger. (The flexibility, cost, and practicality of charging many of these batteries is the primary appeal. Keeping 32 NiMh charged each day, or ten 18650's, isn't practical. Keeping 6 agms going is. And a pound on tool belt is nothing.)

As far as the test I did-if anyone interested: first ran one xre in parallel with one xrc, off 6 volt sla and one duracel 2650 NiMh (7.2 volt) 300 milliamp at start and only %10 drop in current to 6 hours. Then at about 8 hours the NiMH died, so I put in new NiMh for 270 milliamps, ran till hour 10 or 11 to 255 milliamps, then recharged the Lead acid.
Second test: same battery setup, except now with LSD 2100 china kodak. New head: xrc plus Rebel 80. The new fresh current draw is brighter 400 milliamps, due to lower forward voltage of the Rebel. I also have a Rheostat on the rebel head, so can throttle back to 300 milliamps, and in real use can be opened up as current falls %10 or %20--the NiMh should be swapped at 6 hours whether need it or not.