Many devices have built in charge controllers that stop charging when battery is at 100%. I read several places that you can charge devices with the manufacturers recommended voltage and that higher amperage sources will not hurt as the device will take what it needs. True?

Given this, why do portable lithium battery packs (for example a 240WH Lithium pack I know charges at around 40Watts) recommend charging sources be of a limited Wattage? For example if the battery pack has a 12v 3a charge port, any reason I can't plug in a 12v 19a source? Same question regarding a 12v 3a fan, any reason I can't plug in a 12v 9a source?

UPDATE: Part of the reason why I am asking is that I am trying to find a way to charge a 240 WH Lithium power pack with a 200w 18v 11a (max/ideal) solar panel without using another battery. I thought If I just stepped down 18v to 12v with a dc-dc regulator that would be good enough. The manufacture just keeps saying, no more than 100w solar panel.

I guess I need clarity on these NOOB questions:

**(1) Why does the amperage of the power source matter if batteries have a high amperage capacity (2) How do charge cables limit amperage and can this be directly implemented from a solar panel? (3) is there difference in the way battery sources and solar panel sources make available or push power?

I know this is not a typical solar setup.. i'm just looking to leverage a big panel during solar hours without a battery bank These are the products:

My Solar panel is 200w 18v 11a. CHAFON 200Wh Portable Generator Power Station Rechargeable (but want to consider other like Jackery 240). MaxxAir 4401K 4 speed 12v 4a fan. Alpicool C15 12/24v 50watt Freezer. Nextrox DC/DC Converter Regulator 24V Step Down To 12V 20A

Trying to find a way to run and charge these ONLY during solar hours directly (without tying my battery and trusting Low Voltage Disconnects). The freezer supports 12v and 24v. One person at Chafon said no more than 22v, another said no more than 100w input.

I read the duplicate question/answers and it only seems to confirm my suspicion that more amperage availble in the source should not hurt my devices.. but I am still puzzled why manufactures state a limit the input wattage? I understand the Just do what the manufactures says to do and that would be safe I guess but also really complicates the solar panel setup.


**UPDATE: Thank you for comments. somebody on another forum confirmed the Chafon 200wh BATTERY PACK could charge directly from a 12v battery which of course has a lot more watts than the recommended unless fused . For my own understanding and to rephrase the question, what's the difference between power from a 12v battery vs power from a 200 watt (18v 11a) solar panel that has been reduced to 12v. Is the issue that a solar panel is pushing/forcing power where as a battery is offering stable/waiting power ? And how does this apply to a 12v device wanting to charge at 40watts vs a fan that operates at 40watts **

  • \$\begingroup\$ Hi (a) IMHO mixing the fan question with the battery pack charging question is a bad plan; they might have different answers. (b) This type of question, where someone has a specific device, and then tries to ask general questions, often ends badly. As in this case, there isn't enough detail about the specific device, to extrapolate a general answer which definitely applies everywhere. (c) Some of your terminology & generalisations seem wrong, making it even more difficult to answer :-( (d) Please add links to the specific battery pack datasheet & the quoted manufacturer recommendations. \$\endgroup\$
    – SamGibson
    Feb 21, 2019 at 14:28
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    \$\begingroup\$ If the manufacturer is saying not to do this, then don't do it, at least not with their gear. Find something sold with proper specs, or better yet as a complete solar/battery system. \$\endgroup\$ Feb 21, 2019 at 15:14
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    \$\begingroup\$ @ChrisStratton "If the manufacturer is saying not to do this, then don't do it" That's obviously true. However, given the lack of clarity in parts of the question, then one possibility is that the manufacturer isn't saying that. Instead, there might be a misinterpretation by the OP regarding max allowed external current source vs. max internal charging circuit current used. Hence why I asked for links to the datasheet and these quoted manufacturer's statements. Let's see what (if) the OP replies. \$\endgroup\$
    – SamGibson
    Feb 21, 2019 at 15:31
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    \$\begingroup\$ @Hell.Bent - I did some searching for the required information, to try to progress this. I couldn't find a proper datasheet or user manual online for the "CHAFON 200Wh Portable Generator Power Station Rechargeable". However on this (apparent manufacturer's) Amazon page I saw that someone (you?) asked this question 2 days ago mentioning the same "200w 18v 11a solar panel". The manufacturer(?) explicitly says >100W solar panel may cause damage, but without explaining why. So you are correct... \$\endgroup\$
    – SamGibson
    Feb 21, 2019 at 21:05
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    \$\begingroup\$ ... that this statement is coming from the (apparent) manufacturer. However, as Chris points out, without them explaining why, and without you providing a schematic diagram for readers here to examine to try to understand why, we don't have enough information to explain their statement and could only speculate (which is not the mission of this site). Sorry for that conclusion. (P.S. I keep saying "apparent" manufacturer for "Chafon", since at least one other company seems to brand the same product as theirs.) \$\endgroup\$
    – SamGibson
    Feb 21, 2019 at 21:06

1 Answer 1


Not true.

You're mixing up the specification of a charge controller with that of a battery.

Each battery type has a 'preferred' way of getting charged - constant current, constant voltage, or (often) a mix of those over time.

A charge controller is connected to a power source (most often constant voltage, like USB 5v or mains, but I guess constant current or a mix, like for solar power is possible too) and outputs whatever voltage/current 'pattern' the battery requires for most optimal charging given the user requirements/settings (fast, slow, trickle...).

The reason most batteries will have a maximum charge power rating is simply to prevent excess heat from building up.

To make things more complicated, modern batteries often have a built-in charge controller - mostly to prevent mishandling from causing fires...

  • \$\begingroup\$ I based the question on this post: superuser.com/questions/600401/… But really I am trying to find a way to charge a small lithium 240WH power pack with a 200w 18v 11a solar panel and a 24v to 12v stepdown regulator directly. The Power pack has a build in charge controller but says not to charge with more than 100w.. but I wonder if they just don't want more than 12v. Wonder if it's charge controller is specific to solar? \$\endgroup\$
    – Hell.Bent
    Feb 21, 2019 at 11:28
  • \$\begingroup\$ What about electronics that do not charge like a 12v 3a dc fan, what happens if I plug in a 12v 13a solar panel (or stepped down solar panel source)? \$\endgroup\$
    – Hell.Bent
    Feb 21, 2019 at 16:42
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    \$\begingroup\$ Without knowing more about the power pack your first question is hard to answer. On the solar panel, does it have a solar controller? 18v/11A is not what you'll get out of the panel as a panel's specs are generally it's open-voltage and short-circuit current. At DC fan will generally draw as much current as it needs from the supply. Most appliances expect constant voltage and will draw as much current as they need. That's for example why your mains supply is 'fixed' 240v (or 110v, depending on where you live). \$\endgroup\$
    – RJR
    Feb 22, 2019 at 1:17
  • \$\begingroup\$ btw - a 240Wh power pack isn't considered 'small' (unless you compare it with a UPS plant). A normal laptop would have around 40Wh. \$\endgroup\$
    – RJR
    Feb 22, 2019 at 1:19
  • \$\begingroup\$ Thank you for comments. somebody on another forum confirmed the Chafon could charge directly from a 12v battery which of course has a lot more watts than the recommended . For my own understanding and to rephrase the question, what's the difference between power from a 12v battery and power from a solar panel? \$\endgroup\$
    – Hell.Bent
    Feb 25, 2019 at 13:01

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