Is a battery a resistance device, or a capacitance device?

[sun walker]

I'm having trouble finding an answer to this question.
Even on the same thread of 'https://electronics.stackexchange.com' (below) they disagree & in the video section, 1 guy says as long as the voltage is correct you can use 100A to charge an ipad that only needs 1.5A for li, while a vid next to it for sealed lead/a says no - excess amps will destroy/cook the batt.

If my array of SCC's put out collectively 100A, 48v batt, then I assumed I'd have to match that to an applicably large batt bank, eg I can't put a 48v 6 amp hour batt on the end of it, or an array of super capacitors that the spec's say have a maximum input of 3 Amps.

Some say use this V = I x R

Others say No use this W = I x V (incidentally I assume that's correct for the super caps, but then if the super caps are connected to a batt - then the inrush current drawn will only cause approx 1 volt between the caps & batt, so Amps drawn from batt will be limited).

Misc. Looks like my 48v system will be lead acid, li at this time is too pricey for me. So now I'm thinking in order to keep my 12v led light system in the house I'll use 4 x 6 Ahr li batt in parallel (spec's max 3 A per batt input, so 3x4 =12A. So a li batt charger connected to the 48v input inverter. The charger probably Hiyiton 12V 10A, or less amps, I have read that less amps is bad for the batt??? but I don't understand why that would be. There seems also to be disagreement if such a charger will give only the amps the batt needs (draws). In other words the batt will only draw the amps it needs even if the charger has infinite amps available, Same ? as above I guess.

Can I use a charger with more output amperage than the device needs?

I've just bought a portable battery, but the portable battery don't comes with an adapter for the house current; it only comes with a USB cable so I can charge it with my laptop. My mobile phone came

superuser.com

 

[sunshine_eggo]

Not smart enough to answer the specific question, but I can provide a practical answer.

A battery is a load to a charger.

If your charger can supply more amperage than is healthy for the battery, you will get those amps UNTIL the battery voltage has risen to the absorption voltage where voltage is held and current tapers to whatever is needed to support that voltage.

LFP needs to be charged at no more than maximum rated current. Charging at less is a non-concern. A 10A charger on a LFP battery bank rated for 12A is fine.

Your concerns are more appropriate for lead acid. FLA typically requires charging within 0.1 and 0.15C. AGM between 0.1 and 0.2C (sometimes 0.3C). Charging at lower than .05C may encourage sulfation. Charging at higher rates will degrade them.

C = C20 rate, e.g., for a 100Ah battery, 0.1C = 10A.

 

[mciholas]

The problem here is locating the actual "charger" the thing that regulates the current and voltage presented to the battery during charging.

For an iPad, the charger IS NOT the external power supply despite the common assumption it is. The charger is internal to the iPad and even if you provide an iPad with a power supply capable of 1,000,000 amps, the iPad will only use what it wants to use and the battery is protected. If you switch external power supplies (aka "chargers") on the iPad, one might charge faster than the other, but this is only because the iPad charging logic has determine it can draw more power from one than the other without overloading it. Figuring out exactly how much power a device can draw from an external source (like USB ports and hubs) is quite complex.

For the large solar batteries, the charger IS the external source. The BMS can prevent abusive charging, but it does not regulate it. If the external charger tries to pump 1,000,000 amps into the battery, the only recourse is that the BMS faults out.

A battery is neither a resistance or a capacitance, it is a chemical reaction controlled by the flow of electrons.

Mike C.

 

[hwy17]

You can't wire batteries in series and parallel at the same time. Sort of sounds like you were getting at that.

 

[Hedges]

Battery can often be considered a voltage source with low resistance in series.
As people above said, charge controller is key. That may be CV/CC, delivers up to a fixed voltage or up to a fixed current.
To charge any battery, you want to limit current to allowed level and limit voltage to allowed level.

Lithium too expensive, will go with lead-acid?

Maybe Walmart FLA batteries are cheaper than lithium, but these days LiFePO4 can be bought for same price per gross Wh capacity as decent AGM, delivers more total Wh capacity (90% DoD rather than 70% DoD), and has about 8 times the cycle life.

There are some issues & disadvantages to various lithium batteries, but you should evaluate and decide if lead-acid is really best for your system.

FLA typically wants 0.13C charge rate. AGM may want 0.2C. Lithium usually accepts anything between 0C and 0.5C, so a better match to variable surplus power from PV after loads. (Oh, Sunshine just address that. Except my AGM say even 5C OK for a while, if temperature isn't too high.)

I have AGM, oversize PV, SCC set for constant 0.2C

 

[outsider]

Unlike a capacitor, which, other than the destruct voltage doesn't have any special preferred voltage, a battery has a specific chemistry associated with the redox potentials of the exact electrochemical reactions taking place. (In a capacitor, energy is stored as an electric field, which is voltage-agnostic, although the energy goes as V^2, but in a battery the energy is stored as a specific chemical reaction, which has a specific voltage potential associated with it, e.g. 2.0 V or 3.2 V per electrochemical cell.)

So to view a battery as a capacitor, the capacitance changes wildly with applied voltage. It takes hardly any current at all to get a battery up from 0 V up to the "0 % state of charge" voltage (which is above 0 V), i.e. being the equivalent of a not-very-big capacitor, but then it takes an enormous current to actually charge the battery from 0% state of charge to 100% state of charge, during which time the battery voltage changes not very much, which would then correspond to an absolutely ginormous equivalent capacitance. After that, the voltage rises relatively easily beyond 100% state of charge, i.e. making it look like the effective capacity drops again - and the battery becomes at risk of being destroyed as a result of this overcharging.

In addition to that, batteries also have an equivalent series resistance, such that some of the charging power is dissipated by this resistance (i.e. and doesn't end up as useful energy in the battery) and if you charge at a higher current, relatively more of the charging energy is dissipated in this way.

Incidentally it takes a certain voltage drop to force a given current through a resistance, so in order to put, say, 100 A into a battery, the charger terminals have to be at higher potential difference then what actually appears inside the battery, because of the IxR voltage drop of both the charging wires as well as the battery's internal resistance, and this may be enough of a voltage difference deducting from the supply voltage that 100 A won't flow, even if the charger is a "100 A charger". It would only be a 100 A charger if the cables have low enough resistance, and the battery has a low enough internal resistance, to accept all 100 A. OTOH if you connected a smaller battery to a giant supply, you could indeed force 100 A into it by grossly overvolting the supply above the recommended charging voltage of the battery. This would at first heat up and then later destroy the little battery, but you should/would know you are doing something wrong by turning up the voltage so much to get the current up to 100 A.