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Old 04-02-2021, 17:12   #1
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???Multiple sources of DC voltage being fed to battery bank???

I really don't understand how multiple sources can be feeding battery bank. How does it work? Do and don'ts etc.

take a typical boat that has solar panel, engine, generator and battery charger. How does it work?

Case #1 - Boat is sitting at the dock, sunny day, solar panel is putting out voltage. Charger is managing house batteries. What is going on?

Case #2 - Cruising - Engine on putting out DC voltage into house and starter batteries, solar panel is on (sunny day). What is going on? Do's and dont's.

Case #3 - Case #2 but add now that the independent generator is on putting out AC and the charger is on managing the batteries. How does this work? Can this work? Does the engine alternator and battery charger compete? Do's and don'ts

I really don't understand this. Thanks
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Old 04-02-2021, 17:19   #2
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Re: ???Multiple sources of DC voltage being fed to battery bank???

Think of the batteries as a bucket of electricity.

It's possible to pour water from multiple sources into a bucket at the same time, and also to do that while water is leaking out of the bucket.
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Old 04-02-2021, 17:45   #3
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Re: ???Multiple sources of DC voltage being fed to battery bank???

I love MarkSF's analogy

and to extend it further. If you were actually pouring from other containers into a bucket it might be possible to overflow (overcharge and harm your batteries). But decent charging systems (whether alternator, or generator, or solar) are like a pipe with a float valve (same as in your toilet tank on land); as the bucket gets full they slow down the amount going in until it either stops or just matches the amount going out. If each of your chargers has the same voltage setting they will see the voltage on the common connection and reduce or stop charging as that voltage is reached, regardless of how many sources you have.

Hope that helps...
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Old 04-02-2021, 18:09   #4
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Re: ???Multiple sources of DC voltage being fed to battery bank???

The water and bucket are a good analogy. Sometimes all those sources do not play nice and the batteries can suffer. Just have to see how it all works out in the real world, but the water flow concept is accurate way to think about things especially the leak part.

My Victron solar controllers play nice with my AC battery charger and Balmar alternator, but sometimes they fight among their selves (3 ea). No harm done in this case they just call it quits a little early. "I think we ought be in float, I think we should be in absorption, Hell I am just going home".


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Old 05-02-2021, 12:56   #5
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Re: ???Multiple sources of DC voltage being fed to battery bank???

https://www.amazon.com/12-Volt-Bible.../dp/0071392335

The 12-Volt Bible for Boats is a clear, nonthreatening introduction to the 12-volt electrical systems used on small boats to power everything from reading lights to bilge pumps. This second edition is thoroughly updated with respect to modern batteries, breaker and panel design, alternative energy sources, and troubleshooting equipment, but it retains the fundamental simplicity that is the source of its enduring popularity (more than 100,000 copies sold).
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Old 05-02-2021, 13:32   #6
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Re: ???Multiple sources of DC voltage being fed to battery bank???

You can have as many charging sources as you like however each one of them must have a blocking diode to ensure that the current can only flow one way otherwise they will short out and flatten the batteries when they are not charging them.
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Old 05-02-2021, 14:00   #7
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Re: ???Multiple sources of DC voltage being fed to battery bank???

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Originally Posted by RaymondR View Post
You can have as many charging sources as you like however each one of them must have a blocking diode to ensure that the current can only flow one way otherwise they will short out and flatten the batteries when they are not charging them.
you can't make a blanket statement like that.
Does my alternator have a blocking diode on it's output - NO. Does my alternator drain my batteries - NO.
substitute charger for alternator. still NO.
Solar cells directly connected to battery (which is bad idea for many reasons) YES this can cause a drain on your batteries.
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Old 05-02-2021, 15:19   #8
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Re: ???Multiple sources of DC voltage being fed to battery bank???

My solar panel has a controller. I just talked to my electrical guy with 40 years of experience. He said the device with the highest voltage will provide DC to the batteries. The others will shut down (their controllers will).

I have a Magnum charger
Solar Panel with Blue Sky Controller
Balmer alternator with Balmar controller

All thoughts are appreciated.
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Old 05-02-2021, 15:41   #9
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Re: ???Multiple sources of DC voltage being fed to battery bank???

Quote:
Originally Posted by jayarmstrong View Post
My solar panel has a controller. I just talked to my electrical guy with 40 years of experience. He said the device with the highest voltage will provide DC to the batteries. The others will shut down (their controllers will).

I have a Magnum charger
Solar Panel with Blue Sky Controller
Balmer alternator with Balmar controller

All thoughts are appreciated.
Multiple charge sources are not a problem. If charging say with solar and shore charger (at the same bulk voltage setting) one of the sources will go into float before the other. This usually isn't an issue as the batteries are close to fully charged by this time.

One thing to keep in mind is that you cannot pour current into batteries. The current is supplied at a given voltage and the battery bank takes what it needs. Assuming the supply is greater than acceptance the only way to get the battery bank to accept more current is to increase the voltage.
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Old 05-02-2021, 18:58   #10
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Re: ???Multiple sources of DC voltage being fed to battery bank???

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you can't make a blanket statement like that.
Does my alternator have a blocking diode on it's output - NO. Does my alternator drain my batteries - NO.
substitute charger for alternator. still NO.
Solar cells directly connected to battery (which is bad idea for many reasons) YES this can cause a drain on your batteries.
Sure I can. Your alternator does have a plethora of diodes in it.

We used to have DC generators on autos. In these gadgets the coils in the rotor spun inside a magnetic field generated by the field coils and the current generated flowed out through copper terminals on the rotor end via graphite blocks, this was called "the commutator". Now each coil winding generated an alternating polarity current as it spun 360 degrees within the field coil generated magnetic field and making it go the same direction was why it required "commuting".

Alternators reversed the process. The rotor coil generates the magnetic field and the output current is taken from what were the non rotating field coils on the outside casing. However since it is not being commutated it comes out as AC and has now the be rectified to turn it into the DC required for battery charging. To do this a diode plate is fitted inside the alternator.

So there you go mat, your alternator has a plethora of diodes hidden inside it and it is these which stop shorting out the battery and flattening it when the alternator is not running.
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Old 05-02-2021, 20:29   #11
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Re: ???Multiple sources of DC voltage being fed to battery bank???

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So there you go mat, your alternator has a plethora of diodes hidden inside it and it is these which stop shorting out the battery and flattening it when the alternator is not running.
But if an alternator is left switched on (energised) it will certainly drain a battery.

I have three alternators, one is the standard alt fitted to the Yanmar and switched on/off with the ignition key, the other two are big-frame alts mounted about-face on a seperate bracket, driven by the crank pulley and the fields are independently switched from the main electrical DB. This way I can run the alternators that I need/want by switching the fields on or off.

But if I stop the engine and leave the fields on the two big-frame alts switched on (something that I have accidentally done more than once ), each alt will continue to draw about 4.5A until the batteries are flat. The key give-away is that hours after the engine is stopped, the alternators will still be warm.
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Old 05-02-2021, 20:36   #12
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Re: ???Multiple sources of DC voltage being fed to battery bank???

Most chargers first observe the voltage on the wire before applying their own current to the system. To charge batteries the charger supplies higher voltage to the electrical system.

Once a charger starts supplying charge the voltage of the system goes up.

Other chargers see the voltage is higher and either apply higher voltage or reach their cut-off voltage and stop charging.

The voltage the charger(s) supply is higher than what is being observed on the wire because there is also a load (the batteries, other systems) on the wire pulling the voltage back down.

It rapidly becomes a balancing act.

However! I have seen all three of my solar charge controllers and the boat's main shorepower charger all putting power into the batteries at the same time (batteries were quite low). When the battery voltage nears full the solar chargers (with or without shore power attached) will begin to backoff how much they supply, usually leaving one charger delivering power until full.

With some of these kinds of equipment you can have one device read the line voltage and tell all the other chargers how to perform. Victron does this - I still need to configure it on my hardware. Lazy! And it works mostly well even without it. I think there's another couple percentage of charge rate I could pick up by having them talk to the BMV for mutual line voltage.
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Old 05-02-2021, 20:44   #13
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Re: ???Multiple sources of DC voltage being fed to battery bank???

Quote:
Originally Posted by CassidyNZ View Post



But if I stop the engine and leave the fields on the two big-frame alts switched on (something that I have accidentally done more than once ), each alt will continue to draw about 4.5A until the batteries are flat.

Easily solved I would think. Add relays to the fields so that in each case the alternators cannot be activated without the ignition being on.

I use this system on my own boat.
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Old 05-02-2021, 20:52   #14
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Re: ???Multiple sources of DC voltage being fed to battery bank???

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Easily solved I would think. Add relays to the fields so that in each case the alternators cannot be activated without the ignition being on.

I use this system on my own boat.
Thanks for the advice but I’ve had this system for a looong time and have become totally indoctrinated by the ritual of shutting down which includes checking the switching - haven’t had an “accident” for several years now. I was simply making the point that the diodes inside an alternator that is not running will not prevent discharge of the batteries.
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Old 05-02-2021, 20:54   #15
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Re: ???Multiple sources of DC voltage being fed to battery bank???

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My solar panel has a controller. I just talked to my electrical guy with 40 years of experience. He said the device with the highest voltage will provide DC to the batteries. The others will shut down (their controllers will).
[...]

All thoughts are appreciated.
Well, my thought is that your electrical guy with decades of experience is either over-simplifying it for you (and other customers) or he learned something 40y ago and never reflected on it, as how wrong he has been all those years...

The real world is more like this: if you have healthy batteries that are somewhat discharged to a level of, say, below 80% (that's called 80% SOC, state of charge), their electrical resistance is very small, hence they can accept or absorb a lot of energy, which is the current that's being fed into them.

Now, your producers all "see" (as in:measure) the voltage on the power bus, say 12.6V for FLA or 13.3V for LFPs. If your solar CC now produces 10A, it's not going to raise the bus voltage until the batteries are charged higher, to say 85% or more. The CC will _try_ to put out maybe 14.4V, but the batteries with their low resistance are pulling that down to wherever they are.

Next you shore power supply also sees the 12.6 or 13.3V and also puts out whatever current it can, maybe 15A. Again the bus voltage doesn't rise at first, but there are 25A going into the batts.

If you then turn on the iron genny, the alternator _tries_ to produce another 40A, if the batts can absorb all that current.

If they do, the voltage is still at the same level of 12.6 or 13.3V but it will now rise a lot faster, since there are now 40+25=60 Amps going in. Without the other two sources, the net current would now be 40A and the voltage rise would be slower.

Finally, as the bus voltage slowly increases because the batteries are getting full, each of those devices will throttle back, depending on its individual setting.
Only at that point one might say: they shut down. Only they don't, they just stop producing energy until the voltage drops back to their lower set point. (Or they go from this "bulk phase" into an absorption phase, depending on their profile.)

You can check all that yourself if you buy, borrow or steal a DC-capable clamp ammeter, turn on the chargers and check each positive lead coming from them, then compare it to the positive lead going into your batteries. It should sum up, minus the cable losses and other consumers that are running at the time.
Note: If you get a negative current on the ammeter display, it just means the current goes the other way. If you clamp the meter on the other way (rotated 180 degrees), you would see the opposite sign yet the same value).

So in short, you can have many sources of current all feeding into one battery bank, albeit every source might behave a little bit different towards the end of this charge cycle. The standard alternator, for example, is the simplest of those devices and just turns off at around 14.4V and back on at its lower threshold/setpoint. It also puts out a pretty bad, pulsed DC which can, in fact, confuse other devices measuring the bus voltage.

Must be the weekend that I have time to write all this... hope it helps you and someone else down the track. I might just copy it into my blog as well, coming to think of it..
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