Battery bank charging

[SteveK]

Keith, you have two 160 watt panels and in ideal case they would produce 30 amps, you are getting 19amp due to shading. In our climate on a good day perhaps 5 hours a day would be 19x5=95 amp charge. OK now I can see this working.

How many solar panels does it take to charge a 100ah battery?

Again we use the same calculation dividing power in watts by the voltage in volts to find amps. Charging your battery at 12 volts and 20 amps will take five hours to charge a 100 amp hour battery. By multiplying 20 amps by 12 volts, 240 watts is how big of a panel you would need, so we’d recommend using a 300w solar panel or 3 100 watt solar panel.
Renogy.

 

[koliver]

Keith, you have two 160 watt panels and in ideal case they would produce 30 amps, you are getting 19amp due to shading. In our climate on a good day perhaps 5 hours a day would be 19x5=95 amp charge. OK now I can see this working.

No, I am seeing a rating on the back of each panel that tells me I might get 19amps in ideal conditions, from each 160w panel. I don't have any metering to tell me what they actually put out. What I rely on is the voltage of my house battery bank, which now rests at 13.5 or better, at almost all times, even first thing in the morning, after the fridge and freezer have been running (not a lot, but still...) since the sun went down. This is better than I ever saw before solar.

 

[firehoser75]

Steve,
Sorry for not answering sooner, but just saw your post. MPPT takes the "extra" voltage and through some kind of electronic "magic" converts it into amperage. I may be using incorrect terms, but you get the idea. My 570 watts of panels (2x285) are often partially shaded but are never fully shaded on the hook. They lay flat and are not adjustable. With this system, I almost never had to plug in or run the generator for battery charging. However, it is not perfect, as on days anchored in Booker Lagoon in the Broughtons with thick fog until 4 PM, the solar panels would not put any "extra" charge into the battery bank. They would however, pretty much "keep up" with the day time electrical use, meaning the batteries only dropped overnight. On over 90% of my days on the hook, my batteries would reach a 100% full recharge well before sunset. Solar panels, especially using a good MPPT controller are definitely worthwhile, and I advise putting as large a capacity (of panels) as you can reasonably install. On those days where it is heavy cloud or fog, having a larger capacity is a good thing, and the added cost (compared to the smaller capacity) is minimal on the scale of things.
If I remember correctly, on bright sunny days (with the batteries down a bit) we would see about 30 amps going into the batteries per hour. Figuring on a 5 hour day for our area is a good estimate for determining max capacity.

The other advantage that solar offers, is on those days you need (want to) run your generator, you can run it for one hour to heat water, and quickly bulk charge your bank in the early AM (like 9AM), and then let the solar "top off" your bank to 100%. In my case it really cut down on my generator usage.


Hope that helps,
Tom

 

[SteveK]

No, I am seeing a rating on the back of each panel that tells me I might get 19amps in ideal conditions, from each 160w panel. I don't have any metering to tell me what they actually put out. What I rely on is the voltage of my house battery bank, which now rests at 13.5 or better, at almost all times, even first thing in the morning, after the fridge and freezer have been running (not a lot, but still...) since the sun went down. This is better than I ever saw before solar.

Now you see the confusion in sorting this out. The calcs suggest otherwise, but I believe you on what it says.

 

[SteveK]

Thanks Tom, It does help. More info is better. I do not have or want a generator.
I have the info from you and Keith to help make decisions.

Thank you both

 

[firehoser75]

Steve,
One more advantage to solar that I forgot to mention is battery life. By fully recharging the bank to 100% (at least more frequently if not almost every day), you avoid the deadly (to most batteries) operating in a partial state of charge. Regular PSOC operation is murder on most batteries (like flooded lead acid, AGM, etc.). The other benefit is the depth of discharge. Solar will recharge every day meaning your bank is not as likely to regularly get "deeply" discharged. My bank rarely went below 85% charge, so I should expect to obtain more cycles in the batteries lifetime than I could expect if they were regularly dropped to 55-60%. At least in theory, obtaining a longer battery life should offset (at least partially) the cost of the solar system install. Not much maintenance is required either (wash the panels)

 

[Datenight]

Hi Steve,

I know I'm late to the party but have some info that more or less supports other replies. We have a North Pacific 45 with a Summit AC refrigerator, a 40" TV (which we only used once last summer to stream a movie), microwave, Nespresso coffee maker, electric head, Fusion Stereo (use that a lot) system and the usual computers and phones. All lighting is LED. Cooking is propane.

We have 600 watts of solar with a MPPT controller. Panels are flat on the hardtop and pilot house. Batteries are at 100% by 11:00 am every day the sun shines. On a bright cloudy day it takes until about 2:00 pm. Have not had the boat out for multiple cloudy days so don't know how that would work but there is always some gain or at the very least a slower decline.

The generator is often run for half an hour to make hot water for showers. I would like to look into a DC element for the water heater to take the extra watts from 11:00 on.

We plugged in once at our home dock after the service was upgraded to 50 amps to be sure it worked. Also took dock power in Boston to run the AC.

Solar works very well for us. I should have mentioned we are in Southeastern Connecticut about 41* N.

Rob

P.S. Diane always runs the hair dryer after her daily shower.

 

[McDan]

Can anyone explain why we charge DC battery banks using an AC generator which actually produces AC, operating at 1800 RPM for 60 cycle sine wave then run it through a Charger/Inverter unit which in turn supplies a DC current to the battery bank? When the propulsion engine is running it also uses an alternator to charge the battery bank while underway. Wouldn't it make more sense to operate a small diesel charging engine at low operating RPM turning a "DC Generator" to charge a "DC battery bank". Unless there are a lot of AC appliances onboard that need more power than can be drawn from an inverter there is really no need for an AC generating system.

Your modern AC Generator is 3 phase and produces nearly triple the energy of a DC Generator. The DC generator also typically has a commutator and carbon brushes, both of which = maintenance, plus both are highly susceptible to moisture and salt environments.

 

[GoneDiving]

Your modern AC Generator is 3 phase and produces nearly triple the energy of a DC Generator. The DC generator also typically has a commutator and carbon brushes, both of which = maintenance, plus both are highly susceptible to moisture and salt environments.

Don't forget that the general market for AC power supply is much greater than DC. Economies of Scale mean I have the choice between a $500 Chinesium unit or numerous name brands with spare parts and skilled repairs available.

DC generators are essentially one off builds, often for industries with deep pockets (telco, military etc)

 

[High Wire]

Your modern AC Generator is 3 phase and produces nearly triple the energy of a DC Generator. The DC generator also typically has a commutator and carbon brushes, both of which = maintenance, plus both are highly susceptible to moisture and salt environments.

Your engine ALTERNATOR is a 3 phase machine with diodes to output DC.

A house generator is single phase unless for large yachts and commercial boats.

 

[SteveK]

Your engine ALTERNATOR is a 3 phase machine with diodes to output DC.

A house generator is single phase unless for large yachts and commercial boats.

I still remember a starter/generator on some foreign car.

 

[High Wire]

I still remember a starter/generator on some foreign car.

My 68 Beetle had a generator instead of an alternator.