# How do I Integrated various power sources to charge my boat's offgrid batteries?

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I am fitting out my live-aboard barge and am at a loss how to charge my bank of 7 x 110ah deep cycle 12v batteries from 2 x 400/500w  AC 12/24v  wind generators, a 42a alternator on the engine and a 2.8 KVA petrol generator which has a 12vDC 8.3amp output. How do I integrate these power sources to be able to charge the batteries under various circumstances? I have a 12v/230v 3000 amp inverter but have not purchased a charging controller etc yet. I am desperate to get things sorted. Please help/

• Posts: 2,838Registered Users ✭✭✭✭✭
I wouldn't use the DC output of the 2.8kw genny at all. If the inverter has an integrated charger, I would use that. If not, I would get a decent 3 stage charger. 8ADC isn't much, and those outputs aren't generally designed for sustained high current loads like battery charging. The bank will want a charging rate of > 10x that current, which the generator can supply by way of an AC charger (ideally a power factor corrected unit).

The alternator should have regulated output already.

For the turbines, you'll want to look for compatible controllers designed for wind.

There is no problem connecting multiple charge sources to a single bank.

Note that 7 batteries in parallel will need careful monitoring to avoid balance issues (some being overcharged and others undercharged). Each battery should be fused, so a shorted cell doesn't end up being fed by the rest of the bank.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
You have a 770 AH @ 12 volt battery bank... And generally want a minimum of 5% to 13% rate of "reliable" charging current (5% * 770 AH = 38.5 amp to 10% ~ 77 amps). 5% rate of charge can work for weekend/seasonal usage, but for full time off grid, 10%+ rate of charge is usually much better. Depending on the battery type (flooded cell, AGM, Li Ion, etc.), generally a 20-25% maximum rate of charge is about the maximum recommended (that is generally from a genset or shore power). Over 13% rate of charge, a remote battery temperature sensor connected to the solar charge controller is recommended (hot batteries need lower charging voltage set points).

Regarding the 42 Amp alternator--What it will output depends on a lots of things. Good/heavy/short wiring (with fuse) between alternator and battery bank. "Light duty" (aka car/pickup alternators) generally get hot pretty quickly under heavy charging current and will reduce their output current. There are heavy duty truck and marine alternators (with better adjustable charge controllers) that an do better.

For the Wind turbines, it does depend on the specific brand and model of wind turbine. Many are "simple" alternators+bridge rectifier connected directly to the battery bank (through a fuse and possibly shunt/shutdown switch). Those system are "unregulated" and will output as much charging current as there is wind. A second "dump controller" (some simple PWM solar charge controllers can be reconfigured into dump controllers) connects to a resistor bank--They "turn on" when the battery is full (and the wind is charging) to dump excess charging current and protect the battery bank.

Other wind turbines have integrated controllers that may include dump controllers or turbine shutdown circuitry/brakes. Standard horizontal axis wind turbines can and will overspeed in moderate to high winds (to self destruction is possible) unless they are connected 100% of the time to a load/battery bank and/or have shutdown hardware.

I am not a fan of small wind power (you need a tall tower above any nearby trees/buildings/etc.) and a very windy location. Most people do not have good windy locations and if you are a river barge, you may have buildings/trees/terrain that block smooth airflow to your anchorage. Plus few factory built wind turbines seem to provide a reliable/useful amount of energy over time.

For the AC genset with the 8.3 amp 12 volt charger output--That sounds like it is for the genset starting battery and/or used as an "emergency" charger. that is not enough current to worry about (plus some gensets do not like to run the DC charger and AC output at the same time--The small Honda's seem to have this limitations for some of their products). You are much better off getting a good quality 120 VAC (or 230 VAC in your region? UK?) 12 volt battery charger for your battery bank.

Very roughly for a "typical" AC battery charger, you would be looking at a reasonable maximum of:
• 2,800 Watts * 0.80 genset derating * 0.80 charger PF * 0.80 ac charger eff * 1/14.85 volts charging = ~96.5 Amp AC charger for your genset
Iota makes some lower cost, simple, AC battery chargers that work. Xantrex makes the TC2 series (very nice chargers, but somewhat smaller sizes, much more expensive). And some AC inverters are available as AC inverter-chargers (integrated chargers). The AC inverter-chargers can have many setting options which work nice with gensets.

You have a 3,000 Watt (not 3,000 Amp) AC inverter? Roughly, for your 12 volt battery bank, I would be suggesting around 1,800 to 2,000 Watts maximum (both based on the AH capacity of your battery bank and the maximum size of most copper 12 volt wiring systems--And keeping the inverter to battery bank wires short). A 3,000 Watt 12 volt AC inverter needs a very heavy battery bank and wiring to work well:
• 3,000 Watts * 1/0.85 AC inverter eff * 1/10.5 VDC inverter cutoff * 1.25 wiring/breaker derating = 420 amp branch circuit wiring+breaker for your DC battery bus

That is simply more current than most people can design their wiring system for--And you need around a maximum of 0.5 to 1.0 volt wiring/bus system voltage drop--All very difficult to do. For larger AC inverters, a 24 or 48 volt battery bus (and more battery capacity) is recommended.

Regarding multiple charging sources (boat alternator, wind turbine, AC genset, solar, etc.), it is perfectly OK to connect them to your DC battery bus (with appropriate wiring and circuit breakers/fuses). The only issues are--Dump controller need to be properly configured (you don't want your dump controller "dumping" charging current from your petrol powered genset charging), and that all charging sources are properly wired and configured too.

Very roughly, based on the size of your battery bank (not knowing your loads and where you dock), if you could install a solar array--That would be very helpful (saving fuel costs):

• 770 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 725 Watt minimum array
• 770 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 1,450 Watt nominal array
• 770 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 1,885 Watt typical "cost effective" maximum array
Many regions of Europe have pretty glum weather in the winter (even less than 1 hour of sun per day)--Solar does need sun to work (and no shading on panels at all). Many times you are left with running a genset or shore power for winter electrical loads.

Based on your bank size and our rules of thumbs, your bank would be recommended to supply, on average:
• 770 AH * 12 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 maximum discharge = 1,964 WH per day (average)

That is not a lot of power (a typical refrigerator uses around 1,000 WH per day minimum). If you do not have an AC/DC refrigerator, that is a good amount of power for an off grid life style (~1,000 WH per day is not bad for many people).

I will stop here--And let us know what you think of the above--I made lots of guesses about your needs. Note that conservation is a big help with off grid power system (LED lighting, laptop computer vs desktop, efficient water pump, using fuel/other energy sources for heating/cooking, turning stuff off when not needed--DVRs, computer networks/laser printers, electronics, etc.).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 4,008Solar Expert ✭✭✭✭
Flooded deep cycle?  They usually are the best choice for a first time system as they are more forgiving of overcharging voltages if something is not right. Wind generators can be a problem in anchorages if they make a lot of noise. May be worse on a river and with all the deck space you have on a barge, a solar system should be considered. What make of inverter-charger?
"we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
http://members.sti.net/offgridsolar/
E-mail [email protected]

• Posts: 184Solar Expert ✭✭✭
3000w inverter is real big for 12v . Seven 12v batteries oh my . Get some panels and dump the wind.
Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator
• Posts: 1,889Solar Expert ✭✭✭✭
edited January 29 #6
I spent several months studying the liveaboard sailing lifestyle. A lot of sailors invest in wind then pretty well abandon it over time.....in favor of solar panels. They tend to like their solar investment....especially if they find the room for a strong array of fixed panels. Fixed panels are much preferred over flex panels. Continual flexing ruins flex panels which is a bit counter-intuitive in a way. However you already have the wind turbines and you may operate in a very windy location. Wind can happen 24 hours/day which is a strong advantage over solar. But solar is quiet, has no moving parts, and is currently cheap from a historical perspective.

I ventured into wind and was a bit aghast at the need for ~15-30mph wind to operate as wanted. We often have no wind yet wind speeds exceeding 50mph are not rare....with speeds up to 100mph possible. Super high winds have destroyed even some expensive commercial wind turbines.

Seven batteries? I'd stick with six deep cycle batteries. EDIT: OP already has batteries. I would also try to go 24 volt if you garner more than 800 watts of power from solar and wind. This will make your electrical wiring twice as efficient for one thing. Keep your runs as short as is realistic. If you find hot wires, they are really overloaded and very inefficient and likely starving motors and electronics of needed power. Not to mention the fire risk.

I would hope that a 1500 watt inverter would work for you. Perhaps you can use the monster 3000 watt unit when needed? Or trade? The most common mistakes for newcomers may be:
1) Buying an overly large inverter. Like large car motors, they burn a lot more just idling away.