Panel for shed to top off power tool batteries

[PV_Pathfider]

Hi! I'm looking to do a very modest solar panel set up on our shed. What I'd like to do is use a panel to charge a 12 volt battery. The battery would be connected to an inverter (wattage TBD) and then I would plug in charging stations for 18v Kobalt and 40v Ryobi power tool batteries. Ideally, the 40v is what my focus will be. The battery is used on a string trimmer that in the summer, I would use only once a week. The way i see it, every Saturday as I'm taking the mower out of the shed, I'd flip on the inverter to power the charger & 40v battery. Usually takes me 50-70 minutes to mow the yard. Once I'm done mowing, I'd turn off the inverter, stick the battery in string trimmer and then trim away for about 10-15 minutes. This MIGHT use up about 40-50% of a fully charged 40v battery. Once I'm finished, the 40v goes back into the charger, but the inverter isn't turned back on to (hopefully) top off the 40v, until the following week when I mow again. So this isn't an application that would require power from the 12v or panel on a constant basis. Admittedly, when plugged into a wall outlet, I think the battery takes a couple of hours to fully charge. But I won't need a full charge for this application. 50% should be plenty With the smallish panel I'm looking at (details below), I'm just wondering if the panel will have enough juice to top off the 12 volt and if the 12 volt in turn will have enough put a charge into the 40v battery. As mentioned in my intro, this is all new to me so there may be some very obvious things I'm missing in my plan or proposed execution. So feel free to correct or comment as you see fit. Just be gentle! Thanks!!!

I'm looking at the 50 watt Renogy starter kit from Amazon. That's about as big of a panel as I want to get for now. Anything bigger may require oversight from The Man and I don't really want to bother w/ local the municipality for this project. What it may lack in some areas, it looks like it makes up w/ the included charge controller and assorted cables and brackets. I'm ok if I'm paying a bit of a premium for a starter kit, vs acquiring these single thread. If this comes close to working, I'm definitely open to upgrading as needed.

Battery would be the tired and true 12 volt 35 amp battery from Harbor Freight. They seem to be the standard for entry level projects like this and doesn't appear that they blow up any more frequently than a Samsung washing machine. If necessary for reaching full on Tool Charging Nirvana, I would consider adding a second battery down the road. But that would be my max from a cost and space perspective.

Inverter... no idea. Again, I don't think I need anything elaborate. Not looking to power the Gratefull Dead's Wall of Sound. If this works or plans dictate otherwise, I'm fine keeping it simple until a need arises to upgrade. So I'm wide open to suggestions.

Per the back of the charger, the Ryobi charger runs on 57 watts. The Kobalt is listed as ~190 (whatever that means). I can take pics and post if that helps. I don't really think I'd ever run both at the same time, but I could see a scenario where I might still need to charge the Kobalt during the cycle I envision for the Ryobi 40v.

Lastly, location... this will be in a weatherproof, rock solid shed. But it still outside. I don't think I'll be doing much trimming when it gets really cold outside, but there's always a chance I'll need to charge in spring and fall when temperatures start to dip a little. I don't really anticipate this set up getting much use in the winter months.

Welp. There it is. My brilliant plan that I came up with after a few drinks. To boil down this long winded post into a few short questions... Is scenario even plausible with the modest set up I'm proposing. If not, am I close or waaaaaaaaaaaaaaaaaay off?

I've been snooping around this board for a few days and I know that there are a TON of smart folks that contribute. So I'm looking forward to the feedback, suggestions, questions and assorted "Were you born stupid?" comments. If this ends up being doable, I'll post updates and picks along the way. THANKS!!!!!!!

[Mike90250]

.........
Per the back of the charger, the Ryobi charger runs on 57 watts. The Kobalt is listed as ~190 (whatever that means). I can take pics and post if that helps. I don't really think I'd ever run both at the same time, but I could see a scenario where I might still need to charge the Kobalt during the cycle I envision for the Ryobi 40v.........

I can tell you what I would do, and you can take it from there.

1) loads you guess at today, will grow, so I'd plan a little larger than you expect
2) Sun does not always shine, any shade and solar panels produce next to Zero. Panels produce 70-80% of nameplate spec
3) I'd use the cheapest 250w panel you can find, they will be about the same cost as a 100w 12v panel, and just as hard to mount properly.
4a) use a cheap PWM controller, you will loose efficiency, but it should be enough
4b) if not enough, a MPPT controller can be chosen instead, but more $
5) cheap 12V, 90ah marine battery no horrible fright stuff, Pep Boys, NAPA auto, Sams..... It will last you 2-3 years
6) high quality 300w Pure Sine inverter, to run the tool chargers from
7) good LED RV camper light for nighttime instead of a flashlight, inside the shed
8) Dual MRBF fuse block from Blue Seas, 1 fuse for inverter, 1 fuse for charge controller & aux 12V stuff (fuses not included)

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A

I have roughly the same setup, ran a half dozen dewalt chargers off it, works like a dream, now I run a string of LED holiday lights year round, in the outhouse.

You can have a cheap inverter or a good inverter. No good, cheap inverters exist. I highly recommend the Morningstar Suresine 300w. Morningstar also makes
excellent PWM & MPPT charge controllers https://www.morningstarcorp.com/products/suresine/

[littleharbor]

+1 on Mike 90250 suggestions.

I can't stress enough to not go the cheap modified sine wave inverter route. I found out the hard way by ruining a half dozen Makita cordless tool batteries on a remote job. In case you haven't had to replace these battery packs, they are very expensive to purchase separately .

[azdave]

I don't get why you would go to all that trouble when you can simply charge the batteries from an outlet. You don't even require charging the power tool batteries for part of the year so why have all the solar goodies sitting there doing nothing nearly the entire time?

[peakbagger]

I too question a good reason to justify the expense. I would just buy a few spare batteries and keep them charged at nearby outlet.

On the other hand its a fun little project you can wrap your hands around and learn things and sometimes that's hard to justify to someone else. I used to build wood strip kayaks, they look real nice and I had fun building them but the reality is for the time and effort I could go buy a "Tupperware" HDPE rotomolded kayak that is practically indestructible for about the same price.

[Sunking]

If you got $500+ to throw away then do what Mike said. Just one caveat on panel and PWM Controller you need to be aware of. A 60-cell 250 watt grid tied panel has a Vmp of roughly 30 volts and Imp of 8.3 amps. If you use a PWM controller will turn the 250 watt panel into a 110 watts. Just the way PWM controllers work

As a note do not fool yourself into thinking you can use say a 100 watt 12 volt battery panel with a PWM controller and have the same power because you would be seriously mistake. A PWM controller turns a 12 volt battery panel (36 cells with a Vmp = 17 to 18 volts) into a 65 watt panel. Only way to get close to panel wattage is to use a MPPT controller.

But if you got $500+ dollars to loose, go for it. Mike does not have a choice, he has no commercial power. Extension cords are cheap as is adding an AC circuit to a portable building without power limitations of solar and does not need an expensive battery replaced every year or two. So be careful what you ask for, or you actually get what you asked for.

[PV_Pathfider]

I don't get why you would go to all that trouble when you can simply charge the batteries from an outlet. You don't even require charging the power tool batteries for part of the year so why have all the solar goodies sitting there doing nothing nearly the entire time?

The whole project is really just for fun. I already have a small panel on the shed to power some LED lights. I was poking around on YouTube and amazon and found the $100, 50 watt bundle from Renogy and started thinking about what I could power off of it. Since I store moy power tools in the shed, figured I

[britanyweel]

The idea is great, it will help in the household. I know people who do it, but it's not for my back and age. I can barely use a percussion machine, let alone put that much physical effort into it. Even the impact drill I had to buy was based on certain parameters that I could determine at <URL removed> They had a good description of what a light drill sounds like, and I went with their suggestion. I don't know how useful it would have been to buy a random drill. But I'm sure it would have been a mistake. Fortunately, it worked out fine.

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