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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 04-14-2007
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Where does the power go???

Hypothetical.

If I have 2 x 105amp AGMs in a bank for the house and one 80amp AGM on its own for the engine and anchor winch.

If I have an 85W solar panel a wind generator and the engine has a 70amp alternator,

If my batteries are fully charged where does the extra power go given the solar = 5Amps wind = 20Amps and the engine is running?

And if I add 2 more 105 amp house batteries do I keep them separate from the other 2 so I cant flaten the lot or do I keep them in the same bank, if so why.

As you can tell I have no idea when it comes to 12v DC.
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  #2  
Old 04-14-2007
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Simon...first...if you add new batteries, keep them all in one bank, you will get more efficient charging and easier monitoring and maintenance charging. Your regulators and charge controllers work to prevent current from flowing when the batteries don't need it so essentially you have no completed circuit OR a throttled down circuit where any excess amperage is dissipated as heat.
Particularly with AGM's and excess charging capability, you would benefit from adding more batteries as they can accept any amount of current (Amps) you throw at them during the bulk charging stage.
As an aside...I would suggest to you that you are not getting anywhere near 20amps out of a wind generator in normal weather. If the wind is blowing 10-20 knots...typically the amps are in the 6-8 range...but in 24 hours that is enough still over 100a/H's. I averaged 3-4 amps from mine or 80-100a/h per day at anchor as there were many times when there was light or no wind. If your generator has similar output...and you get the 1/3 "rule" output from your solar panel then you should be averaging around 100 A/H's per day from your passive systems. That is enough for many live-aboard to keep the batteries fully topped up ut it all depends on your own amp usage...mine averaged 150-200 A/H's but I am an admitted watt hog! Hope that helps a bit.
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Old 04-14-2007
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First off Simon, no energy transfer is 100% efficient. Because your charging sources are putting out a certain amount of power it does not mean that all of that power is going to reach your batteries. There are losses, in the form of heat, that while minor do reduce the effectiveness of the recharge. Let's ignore those for this hypothetical discussion.

Also, your charging sources are rarely operating for long periods of time at 100% rated capacity. So the total amperage that will be varying widely in terms of what is reaching the batteries at any given time. You now know basically everything it took 70 plus pages of the Solar thread to communicate.(G)

Each of your recharging systems has, or should have, a controller, or regulator, that serves to regulate the amount of energy being sent to the batteries. Assuming we are running all three at once consider, hypothetically, that all of their energy is entering a funnel, at the bottom of which is your battery bank. If your battery bank is discharged, which due to the nature of batteries we consider to be at 50% of charge, the funnel is letting all of the charge through to the bank. As the charge in the batteries is restored, and usually at or around 80% of charge, the funnel starts to constrict at it's bottom. This is a function of the batteries themselves. It is called acceptance. As the batteries get closer and closer to full charge they will only accept energy at a reduced rate. The only way to get them to 100% of charge is to continue to supply current to them, at a reduced rate, for a period of time. As a very rough rule of thumb, it takes about the same amount of time to raise them from 50% to 80% as it does to go from 80% to 100%. This is why most boats are generally operating in that 80% range. It takes the same amount of diesel fuel to run an engine, and it's alternator, to get that last twenty percent as it did to get the first 30%, maybe more.

Now when your batteries are fully charged, the charging devices continue to operate but their controllers, or regulators, will only send to the battery what it will accept, the rest is shunted and lost to heat or the charging device is automatically disconnected. The latter is basically what an alternator does-it only switches on when the voltage is low. If these charge limiting devices were not present we would "cook" our batteries. For instance, when charging a wet cell and we are trying to force too much energy into it, at too great a rate, we will boil the electrolyte in the cells, in the process releasing hydrogen gas, and possibly damage the battery. This is why we need to taper, or regulate, the charge.

Adding the extra batteries gives you a longer operating time in the batteries operating range. Below 50% charge the battery still has energy, but it is not really usable as the voltage drops too low for most uses. So, in practise, we usually end up operating our batteries somewhere between 50-80% charge and anything that lengthens that period will be of value to us. Extra batteries do just that. You would wire them in with your two existing batteries so that the incoming recharge will charge them all at once. If one is out of balance the charge will flow to the lowest charged battery, the one with the greatest acceptance. Due to the variables of our charging sources, both in availability and output, the longer we can extend the time we are operating in that range the better. We will also get more bang for our charging buck on the recharge as our batteries will be at their highest acceptance for our charging time expended. Anotherwords, we can get those four batteries charged back to 80% much more effectively than we can get two batteries charged to 100% and have the same total energy, roughly, available for our use.

I'd recommend that you pull up the archived threads on the topic of batteries. There is a ton of info out there on this. So much, in fact, that if you don't understand what one poster is saying you can skip to the next for another explanation. When you've read all of that, which should be around the year 2525, if man is still alive, you can commence with the reading of Solar World thread. If you get through that you'd probably wish to sell your boat as you'll need the money for long term institutional care!(G)
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Old 04-14-2007
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Thanks guys.
That made it easier to understand. But Say I had one 105 amp battery being charged by a solar panel and the wind generator; these are giving in theory 25amps to the battery. I now run my radar, auto pilot, fridge and stereo pumping out the 1969 hit written by Rick Evans and sung by Zager & Evans(2525). If I understand this right the battery will only accept a certain amount of amps will the battery go flat? I say this because the battery is connected to the buzz bar, or does the extra amps bypass the battery to power the electrics.
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Old 04-14-2007
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I think you mean "bus bar". A bar that's buzzing is probably a fire hazard...

I believe the "extra" is essentially pass through from the charging sources. When I am at dock, I am on 30 amps of 125 VAC shore power, which gives me live AC outlets, plus it runs the battery charger (20 amps max.). If I also fire up my depth sounder, my VHF, my house lights and my nav lights, at some point I will use up all the "overhead" from the charger to the batteries, and will begin to draw down the batteries in the absence of further charging from other sources. Usually, however, when I have shore power on, the charger gets the lion's share of the shore amps, and there aren't many DC draws. The fridge is by far the main draw.

It gets more complicated at sea, where you could conceivably be getting amps into your banks from alternator, solar, wind and even genset. All would have some sort of limiting method to keep you from overcharging your batteries, which are usually always in a state of bailing and taking on water to different degrees, if you follow. As the nature of the wind, the sun and the alternator speed mean differing outputs at differing times, part of that limiting method or technology is to provide a designated charge (say, 13.6 VDC) to the batteries at a given amperage even when the panels are producing 17 VDC. The penalty is a bit of heat produced as waste.
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Old 04-14-2007
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How's this for an analogy:

A farmer has ten piggies at a trough drinking water. The trough (avialable power) holds enough water to satisfy the demands of only 5 or 6 piggies (current draw) at a time. So the farmer has a storage tank (batteries) and he has a hose pipe connected to municipal supply (charging system).

While all the piggies are drinking he points the hose pipe into the trough. If the piggies drink more than the hose pipe delivers, the farmer turns on a tap from the storage tank and lets additional water into the trough to maintain the level. If the hose is not providing anywater, all the water to top up the trough comes from the storage tank.

As each piggy has had enough and the trough starts to refill, the farmer closes the tap from the storage tank and keeps the hose in the trough. When the trough reaches it's optimum level, he points the hose into the storage tank to refill it. Once it is full, he points the hose into a nearby drain (regulators) where it runs off (as heat).

You may have several hoses (wind genny, solar, alternator) and piggies drinking from different troughs (battery banks) and the smart farmer (charging system) will hopefully determine which hose to turn off first and which trough to continue filling

Not meant to insult anyone's intelligence you understand, just a fun explanation (I've always found water to be a great way to explain electricity to kids and grand kids).

Andre
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Old 04-15-2007
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URICA by Jove, I think I may be getting it and no insult is taken. Having read so many articles and talking to the sales people I was becoming more confused. The water analogy is perfect as was all the other replies when examples are given in non condescending terms it all becomes clear, I’m sure these sales people do not have a clue as to the meaning of the prepared spiel they spruik.
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Old 04-15-2007
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I thought piggies and electricity don't mix......er, water and piggies, er.....
Great analogy and discurse Omatako!
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