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rastaman147 avatar image
rastaman147 asked

Help with system to charge 12v AGM battery

I have an Optima D34/78 Yellow Top 12v AGM deep cycle battery (55 AH) that I would like to charge with a 100 watt solar panel. Looking at the GoalZero Boulder 100 panel - The GoalZero rep said this panel will charge my battery and he recommended Victron for a charge controller. So a few questions:

1. Do you agree that this is enough wattage to reliably charge my battery year round, even when there are not a lot of bright sunny days?

2. What charge controller should I use for best results?

Some other information:

Location Pennsylvania, USA, latitude = 40

No trees or other obstacles to the south of panel location. Some trees to the north, east, and west

Distance between solar panel and charge controller / battery ~ 30 feet


MPPT Controllersbattery charging
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4 Answers
JohnC avatar image
JohnC answered ·

Hi @rastaman147

Whether a 100W panel would serve your needs is really dependent on the loads you're applying. That GoalZero is a '12V' panel, and really designed for pwm controllers rather than mppt.

At your latitude this V may be an issue in poor light, and the mppt may struggle to start in such conditions. Victron make pwm's too, and there are many cheapies out there as well.

You may be well served by 2x of those panels wired in series into (say) a Victron 75/15 mppt.

But you really need to determine your load requirements before deciding and spending

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rastaman147 answered ·

I was actually leaning toward the Boulder 200 before the GoalZero rep told me the 100 would be fine, so based on comments I've read regarding actual wattage output on the Boulder 100, I think I will just go with 2x100 as you mention above or maybe the Boulder 200 - would the performance be equal with these 2 options?

Will this controller be a good choice?

https://www.amazon.com/Victron-SmartSolar-Charge-Controller-Bluetooth/dp/B075NQQRPD/ref=sr_1_4?crid=1YV2YY8P8TQ1K&dchild=1&keywords=victron+charge+controller&qid=1588199434&sprefix=victron+charg%2Caps%2C184&sr=8-4

How do I determine the load ? -- I'm using the battery to power a mobile ham radio - Currently, I am using a 120v AC battery charger to charge, and I have a multi-meter hooked up between the battery and the radio, so I can monitor voltage, power, current coming from the battery and watt-hours used,

Or did you mean the load that charging the battery will put on the solar panel(s)?


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JohnC avatar image
JohnC answered ·

@rastaman147

Yeh I meant 'Watt-hours per day' of usage at the ham-radio end. If you can measure it, fine. Then extrapolate out by the hours of use.

There's a configurator tool here: https://www.victronenergy.com/markets/off-grid

It's quite coarse at your level, but you'll get a feel for it. You could even multiply your input data by x10, then divide the 'answers' by 10. Use 24hour autonomy, and your batts (not really needed there) 55Ah @12V @30% drawdown, = ~200Wh useful daily cycling capacity.

With a little luck the app will pick up your location and graph a seasonal estimate for you. Have fun.. Then allow for the really foul days..

For 200W of panel, that mppt in your link is the one.. best you can buy. I'd rather see you buy it from a Victron dealer though, where service comes with it.

But this doesn't remove the '12V panel' thing. That Boulder 200 is still only a '12V' unit, and I'd rather 2x seriesed 100W units in preference. Expensive both are, but you're paying for the portability there I suppose. And you'd likely need to rewire the plugs to series them. Maybe your panel salesman could help there, at least toss in some free plugs.. :)

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rastaman147 avatar image
rastaman147 answered ·

Thanks, JohnC!

I would prefer to purchase from a Victron dealer, as well -- I'm checking out the dealers listed on their website -- Most are distributors, and most of the retail dealers listed appear to be boat / RV dealers that have Victron products -- Can you recommend a dealer who would be good for off-grid end user advice?

Also -- Trying to decide between the 75/15 SmartSolar I linked above with the built-in bluetooth and the 75/15 BlueSolar with the optional bluetooth dongle -- Would be great to find a dealer with the knowledge and willingness to answer my questions, or I guess I could start another thread here with my questions.

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JohnC avatar image JohnC ♦ commented ·

@Justin Cook - Bay Marine Supply USA may be able to clue you up on the USA scene. He's a long way from you, but a prolific poster here. He's been emailed now..

If you want bluetooth, the SmartSolar is the all-in-one option. Perhaps the only use for the dongle might be if the mppt is mounted inside an enclosure and you need better signal with the dongle in a more accessible position.

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Justin Cook avatar image Justin Cook ♦♦ commented ·

Thanks @JohnC!

@rastaman147, I concur with John - the SmartSolar is the way to go unless you have a very particular need for a separate dongle for extending BT range. Generally speaking, a BlueSolar + BT Dongle costs slightly more than a SmartSolar, though, so unless you've found a very good deal somewhere, you'll likely save a little money and have a better and more compact solution by buying a SmartSolar.

I also concur with John's earlier comments... that panel isn't designed for an MPPT controller -very low VOC- so while it'll definitely be better than nothing and will net you some charge over the course of a day, you'll have a much later start to charging and a much earlier end than if you use a higher-VOC panel or -as mentioned elsewhere here- use two of these panels wired in series to get the voltage up.

Feel free to reach out to us if you need further assistance; we may have "marine" in the name, but in fact 80% of our customers are either RV/vanlifers or offgrid customers, so don't be shy. A link to our website as well as my direct email is in my profile if you click through to it.

Cheers!

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