# Tag Info

34

Your point can be very easily made differently. If you look at the discharge curve for a Lead-Acid Battery with a 12V or 6V rating: This comes from Yuasa. They make the things. It's either reliable or optimistic, certainly not pessimistic. Let's look at the 12V one and optimistically assume that you are only interested in 0.2C discharge, any other rate ...

15

Ideally the manufacturer supplies the discharge rates on the battery datasheet. A quick point: You mention you have a 12 V 2.4 A SLA (sealed lead acid) battery, but batteries are rated in amp-hours not amperes. Therefore I suspect you have a 12 V 2.4 Ah battery. Now that we have that out of the way, a 12 V 2.5 Ah SLA battery from Power Sonic, as an example ...

13

Actually SLA batteries have a vent... so the name "sealed" is a bit of a misnomer. VRLA (valve-regulated lead-acid battery) is actually a name for the same tech. Practically every UPS (uninterruptible power supply) I know of has one [or more] SLA[s] inside, so it's generally safe for indoor use. Here's a snippet from an APC white paper on the issue: ...

12

The answers provided so far are a little light on the actual mechanics that warrant balancing on Lithium chemistries and not on others. First of all; all battery chemistries benefit greatly from proper balancing. Balancers are used on spacecraft nickel cadmium batteries, certain types of (low discharge) lead acid batteries and so on. All battery chemistries ...

12

An easy rule-of-thumb for determining the slow/intermediate/fast rates for charging/discharging a rechargeable chemical battery, mostly independent of the actual manufacturing technology: lead acid, NiCd, NiMH, Li... We will call C (unitless) to the numerical value of the capacity of our battery, measured in Ah (Ampere-hour). In your question, the capacity ...

11

Lead acid batteries are fantastic at providing a lot of power for a short period of time. In the automotive world, this is referred to as Cold Cranking Amps. From GNB Systems FAQ page (found via a Google search): Cranking amps are the numbers of amperes a lead-acid battery at 32 degrees F (0 degrees C) can deliver for 30 seconds and maintain at least 1.2 ...

10

Lead Acid batteries have been around far longer than most alternatives - there were no lithium batteries when submarines relied so heavily on batteries. But lead acid batteries also tolerate abuse quite well. The Wikipedia article on the Royal Navy's first submarine, HMS Holland illustrates this. Built in 1902, HMS Holland sank in 1913 while under tow ...

10

Excellent answer from Asmyldof. The only things I'd add is that: (1) There are several distinct varieties of lead-acid: the 'starter battery' that's intended to very rarely be discharged very far, the 'motive battery' intended for gradual & deeper discharge, the 'standby battery' for UPS style operation where deep discharges are rare and so the ...

9

Actually it is possible, but this will ruin the battery irreversibly. The trick is that the fully discharged Pb-acid battery has both electrodes the same composition $PbSO_4$. When the battery is charged, the negative plate contains pure $Pb$ and the positive - $PbO_2$ . This way, if you fully discharge the battery, it can be charged in reverse way. ...

9

A major factor to consider with multi-cell batteries is that damage caused by under-voltage will be concentrated on the weakest cell, but the performance of that weakest cell will be generally the limiting factor with regard to the performance of the pack as a whole. If all six cells of a 12-volt pack are equally good, drawing its voltage down to 9 may draw ...

9

Well, sort of, but not really. The power supply would need to be adjusted to put out about 13.7 volts. This is the nominal float voltage for lead-acids, and is the point you should aim for. There would need to be some sort of isolation between the battery and the supply when power is off, or the battery may back-feed the power supply, and may well damage it....

8

This is not a technical answer but some more fuel for your counter-argument: I used to work in places that had LARGE backup battery banks (100's - 1000's of high-quality batteries) and those got changed out (ALL the batteries) at vast expense if they got cycled below the manufacturer's recommended limit due to a power outage. This was high-reliability ...

8

Probably that battery is not designed for automotive applications. SLA (Sealed Lead Acid) batteries are designed to start car engines, and that requires a peak current that may be several time the C rating of the battery. For example, a SLA battery having 43Ah capacity (and hence a C rating of 43A) could provide a max current of 390A for a couple of ...

7

How could i modify scheme to get rid of lamp and raise its efficiency to 85-95%? You can't, this circuit needs the lamp to limit the current. Without the lamp too much current will flow and battery and/or diodes and/or SCR will blow up. This circuit is very crude and also unsafe and inefficient like you mentioned. That's because it doesn't do anything to ...

7

The max safe current is the CCA rating for 30 seconds max and 30 second intervals. Exceeding this may warp the plates of batteries, boil the electrolyte and with sparks create a safety hazard. A car starter will not exceed this rating when sized properly and the voltage will not drop below 7.5V, which is the criteria used for the CA and CCA test. This the ...

7

I can see a few issues: The UltraFire batteries shown in your photo (and in your calculations) are fake. It is impossible to have 12,800 mAh capacity 26650 batteries. This is similar to my answer here about 18650 batteries. The largest capacity 26650 batteries currently available are less than 6000 mAh. For example: UltraFire BRC26650 7800mAh (Red) - test ...

6

My husband served on R.N subs, and was forced to retire after a leak,these are surprising common, saw seawater enter the battery compartment, bottom of the sub as you guessed and with crawl room only, which released chlorine gas. The result was himself and the C.P.O both having their working careers finished permanenty after dealing with the leak. ...

6

Lead acid batteries are OK with a certain float charge current forever. Lithium batteries would be damaged that way. When a lithium battery is full, trying to charge it more will cause damage. Conversely, in a car the "12 V" lead-acid battery is usually just charged with a fixed voltage of about 13.6 V. At that voltage it will take a small amount of ...

6

Yes it is normal for the water to boil if you are overcharging it, with a too high current. And it is bad. Yes your charging current is set too high. Also check that the final float voltage from your auto charger is correct to the final charging voltage of your battery. From Yuasa batteries (pdf): yuasa techmanual For the correct charge rate a rule of ...

6

...hold about the same number of AH But there's the catch! A big one: The mAh rating for the SLA battery is at 12 V so that equates to: 12 V * 22 Ah = 264 Whr (Watt*hour). But for the powerbank it usually is at 3.7 V (the nominal voltage of a Li-Ion based cell), almost all powerbanks use a 3.7 V battery and a DCDC boostconverter to make the 5 V output. ...

5

These are called spade connectors. They're often available with plastic covers to make them a little bit safer against someone dropping a spanner on the terminals. Here's some with a useful banana plug lead on: Available from Gliders Distribution

5

Short-term, this isn't a problem. You'll end up with ~24V powering the load. Long-term, this is a bad idea. Once the half-charged battery gets drained, the full-charged battery will now be at half charge and will start running the drained battery in the reverse direction. Lead-acid batteries hate to be deep-discharged. The lead plates will corrode and you'...

5

The voltage of a battery droops during discharge because of its internal resistance, which is primarily a function of the ion concentrations in the electrolyte. Because ions must physically move through the electrolyte during discharge, a gradient in the ion concentrations is created, with them being most depleted in the vicinity of the plates. Pausing the ...

5

No, you should NOT fully discharge a Lead-Acid battery. The normal reason for wanting to fully discharge a battery is because some batteries have a so-called "memory effect" - old NiCd cells are notorious for this. But Lead-Acid does NOT suffer from this effect. In addition, you can cause permanent damage to some of the individual cells within the battery ...

5

Because the solar panel puts so little power compared to the size of the battery, and lead-acid batteries are rather forgiving, all you need is a Schottky diode. Connect the diode in series with the solar panel, cathode to battery +, anode to panel + output. Tie together the panel - and the battery -. That's all you need. The float charge level of the ...

5

Just get two car batteries and put them in series. That should be close enough to 24 V to run the device. It is quite unlikely that ±1 V will cause any trouble, although there is no guarantee of that. Since the power supply is rated for 1.25 A, you know the device won't draw more than that. Even assuming the full current draw for 8 hours, that ...

5

Calculating the needed capacitance is easy for a simple parallel cap: 1 microfarad will supply 1A of current for 1 microsecond while dropping the voltage by 1 volt. 1A is a typical steady-state current for a wireless routers, and I suppose most of these can survive an input voltage of 11V, so you roughly need as many farads as the seconds you want your ...

5

Generally it’s a very bad idea due to different discharge curves for different chemistries plus the increased problems with series connection of any batteries. If you do manage to have floating or differential undervoltage protection and balance charging, you could make it work. However, if you need to ask, I would determine you don’t have the skills to make ...

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