Small Solar Maintenance Charger Advice Pretty Please [emoji120]
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I wouldn't connect any panel straight to a battery without a regulator - at night time the current flows the other way.
solar panel ==> regulator ==> battery
Rule of thumb is to pick a regulator that is 125% the short circuit current/Isc of the solar panel (in offgrid use).
The Isc of your 20W panel is 1.21A so would require a regulator that is at least 1.5A
Cheap PWM regulators are basically just a voltage sensing switch which usually cut out around 14.6v and are "okay" for small jobs (10-20w for maintenance). Such regulators can be had for around $10-$15 a piece.
Good quality PWM regulators (Epever/morningstar/projecta/etc) are durable and usually do a 3-stage charge (bulk/absorption/float) and have preset charging parameters for different battery types (sealed/gel/wet). When used correctly they will keep your batteries good for many years. They will set you back around $40-$60.
If you're looking on ebay, many PWM regs are mislabled as MPPT. If what's being advertised appears to be physically small and around $15, they're not MPPT (MPPT is not something you need to worry about for what you want to do).
Last edited by pollenface; 14th October 2020 at 12:00 AM.
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