# Tag Info

30

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 ...

20

In domestic use LiIon (Lithium Ion) batteries are, all things considered, MORE dangerous than "lead acid" batteries, not less dangerous. But both are "reasonably safe" [tm] when used properly. The advice that you linked to above is actually titled "What precautions are needed when charging a car battery in an apartment?" and that is quite different than ...

18

Unlike surface vessels, submarines have to be able to sink. Every cubic foot of air space in a sub must be counterbalanced by almost 60 pounds of weight for a vessel to be able to submerge, and many submarines have a significant quantity of ballast for that purpose. Lead acid batteries have much less energy per unit mass than lithium-based batteries, but ...

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

Can I charge a 12v sealed lead acid with an old wall-wart (not made for charging)? If I use a 1Amp wall wart it should take 7 hours to charge the battery. Would it be bad for me to plug the battery in for 7 hours and then unplug it when the voltage is about 13.5-14volts or so? As an emergency measure it should do the battery little or no harm. You do ...

11

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 ...

11

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 ...

9

There are two kinds (a bit more really, but good enough here) of lead-acid batteries - gel (a few variations) and flooded cell (can be sealed or not). Cars use flooded cell batteries because they are cheaper (UPSs use gel cell batteries). Flooded batteries have liquid electrolyte (sulfuric acid). If you tip over the battery, the acid may spill out and do a ...

9

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

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

In theory it is OK to connect them in parallel with two conditions: Each battery must be in a state where it can be voltage charged. This is fine for lead acid batteries unless they are very run down. Very discharged lead-acid batteries have to be charged with fixed current until they get to a minimum voltage, then they can be voltage charged. The power ...

8

See my stack exchange answer to "Lead Acid Battery Charger Design Factors" which relates, and follow the link there to the Battery University site which will tell you far more than you knew there was to know about lead acid (and other) batteries. From the above answer note the quotes from the above website. Especially in this context The correct setting of ...

8

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. ...

8

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 ...

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

(1) Battery university will supply reasonably good answers to many battery questions. "Lead acid" is a very broad description and there are many subtypes and special types that fall under that description. The terms VRLA, AGM, flooded, calcium ..., pure lead, spiral wound, gel, traction, deep discharge, automotive, SLA, boost, float, CC, CV, ... all are ...

7

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 ...

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 ...

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

There are two important things to know about charging lead acid batteries. There is very very deep and arcane* magic involved, without the knowledge of you are doomed to miserable failure. (*But not necessarily dark). The magic has been very well investigated over 100+ years and there are exponents of the deep and arcane arts willing to share with you ...

6

It's unlikely that your 1A wall-wart will handle the battery load, as regulation tends to be quite poor on many lower-quality models. Don't expect constant-current charging - most likely the voltage will sag as the load increases. I wouldn't assume it to be able to maintain 1A over the whole cycle. Also, some wall-warts don't like being connected to a source ...

6

Fortunately, there is. You can find diagrams of the discharging process of a battery type, search for "lead-acid discharge graph" or so. This returns graphs like this one: In the datasheet of your battery you can find the exact graph for your battery. Say you want a circuit to detect 80% discharged, just check in the graph, the voltage of a lead acid ...

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

...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

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