Solar vs. Alternator Upgrade vs. ???

[Wurlitzer1614]

This topic has been covered many times over the years but in my opinion, technology, prices, knowledge, and parts availability changes frequently so it's worth a revisit.

Fast forward through a Michigan winter and here I am again trying to figure out an additional way to charge our 470Ah (4x GC2) lead acid house bank so we aren't tied to being plugged in at a marina every night.

Currently the original 51A alternator charges the dedicated group 27 engine battery only. The battery charger charges the house bank when on shore power. There is a combiner switch that will connect the engine battery and house bank but I've never attempted to use it. Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections.

We mostly day sail but we would like to take a two week trip go "up north" as we say in Michigan. It's usually difficult to get last-minute transient slip reservations to work around weather and lake conditions so having the ability to anchor for as much as three nights is a must.

Based on my extensive 72-hour energy budget spreadsheet, I estimate 120-150Ah use in a 24 hour period with the fridge mostly empty. With our family of five, the fridge will be completely full so there's a possibility my estimate could be low. (My estimate comes from watching trends on my cheap $20 voltmeter/watt counter and shunt combo from Amazon.) That puts us at 50% SOC sometime during the second night, assuming our batteries are actually relatively healthy. To get amps back in the bank, I see four options:

1. Utilize existing alternator but closely monitor SOC to stay above an unknown threshold that the alternator can handle.
2. Upgrade alternator to 90A or 105A with external smart regulator.
3. Add 2x 200W rigid solar panels on a frame above the bimini. I figure this is about the maximum I could reasonably add.
4. Bring our 3500W generator along. It's noisy, smelly and I don't know where we'd put it or the gasoline but we'd have battery charging, air conditioning, and the kids would have TV.

With options 1, 2, or 3, the big unknown for me is the math of the charging sequence for deep cycle batteries. This is especially true with the solar option where the available amps varies by time of day. I've read (a few times) the thread about battery acceptance but I'm still not clear on the math behind it. Google wasn't much help either. There's lots of information out there about discharging but not much on what's actually happening in the three charging states and what the ideals are.

Reference screenshots of the spreadsheet show two days based on leaving the dock in the morning on day 1 100% charged. One column shows estimated available amp hours without solar and one shows estimated available amp hours with solar and 80% charging efficiency.

Here's an excellent thread on alternators for this type of house bank: https://c34.org/bbs/index.php/topic,9773.0.html

[Ron Hill]

Trevor: I'm really the wrong guy to answer you because I have a battery monitor (Volts, amps and amp hrs.), hi-output alternator, starting battery, 2 flex able solar panels, and a 1KW Honda generator (very quiet) !!!  I usually run the Honda in the afternoon for a couple of hours on the 2nd day at anchor.

Your biggest 24/7 amp user is the fridge - which I've insulated the outside of the box and have a thermal pad for over the lid.  We even put our drinks into a 5 day thermal ice chest so we open the lid only when necessary for food.

A few thoughts

[Wurlitzer1614]

Ron,

It looks like you have a little bit of everything! How big are your solar panels?

I like your idea for adding extra insulation to the box. What did you use on the outside? With three sons that eat pretty much constantly it will be hard to keep the fridge lid closed. Thankfully they aren't quite big enough yet to lift the lid and get food out themselves! I suggested to my wife that we pre-make some meals and deep freeze them before we leave. We'd probably only get 2-3 days of refrigeration assistance from that before they'd be consumed though! For reference, my spreadsheet has refrigeration 75-80 amps/day.

I added a picture of my cheap power monitor and itemized power usage in 24hrs.

[Noah]

Your fans seem to draw more juice than I would guess. What brand fan and how many? Also, you could probably remove steaming light from budget list, as you only run it when engine is on and charging.

[Jon W]

Trevor, peak charging hours for the areas that you'll be sailing in are an important part of the system design. At the state level, Michigan is ~2.5-3.5 hours per day. Californina where I am it's ~5-7 hours per day. Makes a big difference.

[Wurlitzer1614]

Noah- My original Hella fans each draw .15A on low and .25A on high. On a warm night, we'd be running three of them (one in each sleeping area) on high. I put the lights on there for one hour as reference. My lights are powered from the house bank so they aren't charging while the engine is running with my current setup.

Jon- I added a picture of what I estimate I would get out of 400W of panels on an average August day. A state average for MI isn't very useful because we sometimes don't see the sun for the entire month of January. All that matters is May-Sept. There's a fantastic website that will generate a .CSV file for every hour of every day for a year for a specific location:

https://pvwatts.nrel.gov/

The estimator on Victron's website was very close but only has daily averages by month.

[pbyrne]

Maybe my setup will be useful for you.  We are on the St Lawrence River. 

2 x 200 ah (400ah) AGM
2 x 110W Sunpower Flexible
1 x Victron 100/20 Smart Solar Controller
1 x Victron BVM

House batteries do starting as well.

Alternator is stock for a 35B.

We run the fridge 24/7 set to 3-4 on the dial if I recall.  Chilled or frozen food to start the trip is an excellent idea.

I also run the Vesper Cortex VHF/AIS 24/7 for anchor alarm.

Assuming at dusk, the battery is 100%, by morning the lowest I've seen is 85-90% charge.

For fans I have a couple of rechargable portable fans that you can move around the boat to wherever you want them.  I went rechargable for 2 reasons, 1 you charge them during the day and store the energy to use at night which puts no additional drain on the battery at night, and 2 you can move them to the cockpit if you want.  Maybe 3 is as an emergency wind device for calm days... probably not though.

I think these are even better than what I have.  I just ordered one.  https://www.amazon.ca/10000mAh-Rechargeable-Portable-Operated-Treadmill/dp/B0992KV5SK?ref_=ast_sto_dp&th=1

We do movie night with a laptop and use an external power supply with enough ah rating to carry the laptop for at least 3 hours, and the monitor is a 27inch unit that draws less than 18W.

All interior lights are LED, and so is the anchor light.

I'm mindful of the charge at all times, but I've never had an issue. 

I've leaned towards conservation as much as possible as it's pretty easy to do on the boat, and more batteries, chargers, solar, alternators are way more money. 

But.... maybe you would like more power.

[Noah]

Suggestion: I would take a look at the way you have your house bank and start bank wired. The way mine is wired (and is pretty common set-up) is my shore power AND my engine alternator charge my (4 6V golf cart batteries) house bank and I use an Echo Charger to my start/reserve battery. ALL DC loads (except starter) are powered from house bank. I do have the ability to combine both banks in a emergency—but never had to do it.

[Ron Hill]

Trevor : My solar panels are small - about 14W.   The 1KW Honda is the gem!!  It it will charge rain or shine and at great rate and is quiet!! Easy to handle, store and burns little fuel.

There's a Mainsheet tech note article on my fridge insolation.  Essentially I used 3 1/2" foil faced wall insulation cut to go around the outside of the fridge (under the galley counter top).  A piece of foil faced Styrofoam behind the aft dinette cushion, a 1/4" thermal panel on the outside on the stove side and sprayed in foam on the starboard side between the box and the hull.

There is 36 years (TONS) of information in those Mainsheet tech notes and in WiKi on every imageable topic about your C34!!  Just there for the reading!!

A few thoughts

[Jon W]

A good charge controller will have settings for the charging sequence you asked about in your original post. I installed Victron Energy MPPT charge controller's with Bluetooth and a Smart Battery Sense. I'm very happy with them. Since installing the panels, I was surprised that even when skies are overcast my panels are pushing quite a few amps into the batteries.

[Noah]

Trevor: Regardless of whether you add solar or not..., i have questions regarding your statement you made in your original post (see below):

"Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections."

I am not an electrician, but I am not sure what your fear of using your alternator to charge your house bank is or, what citations you read citing the dangers of doing so with an ACR?

[KWKloeber]

I ?think? the point was not the ACR per se.  It's cooking a stock 50a internal regulated alt with a large bank/large energy budget that will need to be replenished after an extensive off-the-grid.  It may be operating at high output for extended periods, which will shorten the life vs installing a large, externally regulated alt.

Trevor: Regardless of whether you add solar or not..., i have questions regarding your statement you made in your original post (see below):

"Last summer I installed much-needed fusing and purchased and installed an ACR but after reading multiple posts about frying original alternators charging the 4x golf cart banks like mine, I didn't make the final ACR connections."

I am not an electrician, but I am not sure what your fear of using your alternator to charge your house bank is or, what citations you read citing the dangers of doing so with an ACR?

[pbyrne]

A good charge controller will have settings for the charging sequence you asked about in your original post. I installed Victron Energy MPPT charge controller's with Bluetooth and a Smart Battery Sense. I'm very happy with them. Since installing the panels, I was surprised that even when skies are overcast my panels are pushing quite a few amps into the batteries.

That's been my experience as well with the same components.  It works well even when cloudy.  You just have to be reasonable.  I tried to use spreadsheets and solar peak efficiency early on with my planning. It didn't work very well.  You can ball park it, but it was better in the end to see what other people were doing, and if they were doing what I wanted to, and they were happy I just went for it.

IMHO, at some point it's just 'analysis paralysis'.  There are too many variables to be perfect.  I think you've got a good perspective on your usage, and if you find a good solar reseller they can help you identify the right equipment for your needs.

What I can say is the Victron stuff seems very good, and so do the Sunpower panels.

[Jon W]

I went with 2 Renogy 175W flexible solar panels on the bimini attached hook and loop/lapel method. Each solar panel is controlled by it's own Victron Energy SmartSolar MPPT 75/15 charge controller. Also added a Victron Energy Smart Battery Sense Temp/Voltage Sensor for the charge controllers.

I came to the same conclusion pbyrne. Be reasonable with your power usage, and the fridge is the power hog. All but two of my light fixtures are LED. Anchor light, nav lights, spreader lights are also LED. Radar, chart plotter are low power.  I do not have an inverter. I've dropped anchor on a Tuesday morning, and picked up the anchor Friday morning and the batteries were 95-100% SOC. The solar panels did all of the charging.

[Noah]

Whether you go for solar or not, i would recommend you still opt for a larger alternator (MR small frame/case variety that uses 3/8 in. V-belt) and an external regulator. You can get a 95A Leece/Pestolite alternator (with external regulation kit) and a Balmer 618 regulator, for approx. total price of $700. Check out Mainsail's www.MarineHowTo.com and his Amazon affiliate link.

https://marinehowto.com/external-alternator-regulation-conversion/

https://www.amazon.com/shop/marinehowto/list/20TSOXZ7R1MMU?ref_=cm_sw_r_apin_aipsflist_aipsfmarinehowto_NSY6PPTQ4YECJAKYQZS1