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I have a 12V 200Ah/20Hour battery and a 60A MPPT Charge Controller. Currently, I only have 200W of solar power to charge my system (planning to upgrade to larger system soon when my proof of concept is done). However my concern is whether my charge controller could charge my battery too fast, causing it to explode. I haven't found anywhere online describing how to calculate whether this will happen or not.

As I understand it, the MPPT controller will output a maximum of 60A but it could be lower depending on the current of my solar panels. Is that correct? And how do I know how much charge current my battery can handle?

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  • \$\begingroup\$ what model charger & battery (cheapo's or good ones?) \$\endgroup\$ – Tony Stewart EE75 Oct 11 '20 at 3:30
  • \$\begingroup\$ That depends on the battery specification. What max charge current rating does it have? Battery chemistry is not specified but charging a lead acid too fast shouldn't cause battery explosions (watch for the vented hydrogen though!) but will cause electrolyte loss. If it's "maintenance free", i.e. unmaintainable, that's a different problem. \$\endgroup\$ – user_1818839 Oct 11 '20 at 12:19
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    \$\begingroup\$ Max Ichg = Power/Vbat = 200W/12V ~= 16A. Battery is 200 Ah so C rate max = 16/200 ~= C/12 = OK rate as long as charger can properly handle the battery type. What chemistry (Lead acid, LIIon, ...)? \$\endgroup\$ – Russell McMahon Oct 12 '20 at 11:48
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NO, a 200Ah battery will not explode here

In general, you can assume any battery can handle one-hour rating in Amps from the Ah rating (20h). So 200 Amps no sweat for a 200 Ah bank.

Good batteries of this type are protected internally for explosion from short-circuiting the terminal, if that is a risk, which might be the only risk from H2 generation and a spark. e.g. Lithium.

Think car starter and welder's cables. Search for your battery datasheets. (BTW what models for MPPT and battery?)

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But for 30 seconds if the CCA rating is 5x this amount or 1000A for 30sec max. with 2 min. delays between for cooling. But due to Puekert's Law the Ah Capacity reduces from 20h std value. So if drained in 1h you might lose 20% capacity more or less depending on quality of chemistry. The life expectancy depends on how well balanced each cell is (Quality Control) and the depth of undercharge or overcharge. undercharge causes lead to rust which corrodes and insulates the conductive lead plates.


If charge is need and charge is available, the MPPT will load the PV with the matched impedance Vo/Io which is the same as Voc/Isc.

Yet the output will be limited by this solar input so Pout cannot exceed Pin.

There would be very little storage for only a few cycles so transients if possible would be harmless.

Car batteries with 55Ah capacity routinely get 100A +/50% typ car/trucks

How much it can handle depends on I^2*ESR=Pd power dissipation which a large 200Ah ought to be able to handle lots. This is rated by CCR for 30 seconds where max current is allowed to drop 5V.

This one has CCA =1450 Amps

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In an earlier answer, I stated that 'Genuinely smart MPPT controllers should 'understand' your battery' as a response to the original question about charge current and whether that could cause battery damage.

I got some 'stick' for that statement, so I need to elaborate regarding my thinking.

I had actually come across some info online a while back that resulted in my making that statement. I may have been looking at an MPPT made by Emerson Electric, not sure now but certainly Emerson do indeed make solar MPPT controllers.

Anyway, I recall that this 'intelligent controller' had a UI that allowed one to input data regarding the battery. Subsequent checking confirmed this to be true.

Anyway, I came across this user manual ...... http://www.mppsolar.com/manual/PCM-60X/PCM-60X-MPPT-3KW.pdf

You'll see that the controller continuously monitors battery condition. I'd post some text from the manual but it goes on for pages ! State of charge and capacity can be monitored by voltage, temperature and dV/dt of terminal voltage as the controller knows all about charge and discharge current. The controller even had an input for the battery 'type'.

So, in conclusion, intelligent controllers do indeed 'understand' the battery and ensure that they're treated well !

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