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Old 24-12-2011, 14:34   #31
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Re: Proper fusing of various charging sources

" that event has just caused a loss of connection from the alternator to the battery, and that will then blow all the diodes in the alternator.
...So now after you find and cure the fault, replace the main fuse, you will also have to replace the alternator."

Usually, yes. But NOT ALWAYS. There are some alternators that have internal protection which will gracefully shut down and limit themsleves if the field or voltage sense lead is disconnected while the alternator is still turning. (You'd have to check the spec to find out.) And there's a gizmo called a "zap stop" which is a special diode that can be added externally to any alternator, providing similar protection. (From an electronics supply, about $5-10. By the brand name in the chandlery, add three markups and it is $25-30.)

Alternator output wiring "always" used to consist of a length of fusible link wire. That is, wire designed to quickly melt just like a fuse. That creates an issue of fire problems, so for a while builders ran a fiberglass jacket over the fusible link wire, to contain the burning bits. These days...if you have an old boat, examine the alternator output wire and if it says anything like FUSIBLE LINK on it, replace that wire with a properly fused one. Or at least, get some non-combustible tubing over it.
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Old 25-12-2011, 06:08   #32
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Re: Proper fusing of various charging sources

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Originally Posted by Waterwayguy View Post
RC, In looking at your sketch, if this were me, I would not connect both chargers as you indicate. There is always the possibility that you might have both chargers on at the same time, not a good idea. You might disconnect the one you want for back up and if one fails, make a re-connection. Chuck
There is no problem running two chargers at the same time as long as the input source and the output cables are sized properly. The batteries will regulate the combined output.

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Old 25-12-2011, 06:10   #33
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Re: Proper fusing of various charging sources

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Originally Posted by hellosailor View Post
And there's a gizmo called a "zap stop" which is a special diode that can be added externally to any alternator, providing similar protection. (From an electronics supply, about $5-10. By the brand name in the chandlery, add three markups and it is $25-30.)
A diode addition like the zap stop MAY save the alternator, but there is still risk of damage and they are one-time use devices. Best to just not wire for the risk.

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Old 25-12-2011, 08:50   #34
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Re: Proper fusing of various charging sources

Mark, i wouldn't call a zap stop (a diode) one-time protection. Yes, it is meant for short interval spikes and yes, continual loads can overheat it and blow it out. But if you don't blow it out, it can and will function for many thousands of events.

OTOH I saw one that had been simply taped into a harness, and BOTH leads had snappd off from vibration. If it is installed, it has to be secured and supported properly, like any other component. Don't work so good when the wires are broken clean off.
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Old 25-12-2011, 09:35   #35
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Re: Proper fusing of various charging sources

What I have found to be "new" with electrical over-current protection (fuses and c/bs) is the concept of excessive current flowing back to what is normally considered a "source." In the modern boat these days there are multiple "sources" of electrical power generally connected together some way or other.

- - Classical sources are batteries; inverters; alternators; solar and wind.

- - Normally you think of protecting "downstream" things from the source and the wire capacity. But now there is a push to protect against electrical fires that could be caused by failures or dead shorts in the sources of electricity.
- - So you now consider adding over-current protection at the source end of power cables to protect them from fire should an electrical short develop in the source itself and excessive power flow from a different source to the failed source device.
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Old 25-12-2011, 09:49   #36
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Re: Proper fusing of various charging sources

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Originally Posted by colemj View Post
There is no problem running two chargers at the same time as long as the input source and the output cables are sized properly. The batteries will regulate the combined output.

Mark
That is not completely correct since the chargers are mismatched and connected them in parallel, there is the potential for one charger getting feedback from the other rather than the batteries and the bank will not get proper charging. Turning one off with a switch is fine but there will be the chance that both could be turned on at the same time. Chuck
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Old 25-12-2011, 18:58   #37
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Re: Proper fusing of various charging sources

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there is the potential for one charger getting feedback from the other
Here applies the famous Hellosailor law of compatibility.
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"Why is it that you can’t use two charges on a single battery bank at once?"
You can, and you can also have two wives and live in perfect harmony. But like the two wives, the two battery chargers may have different idea about reality and contradict each other, and make your life hell. The "smarter" each charger is, the more likely you'll get hell.
Merry Christmas and Happy New Year.
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Old 25-12-2011, 19:22   #38
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Re: Proper fusing of various charging sources

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Originally Posted by Waterwayguy View Post
That is not completely correct since the chargers are mismatched and connected them in parallel, there is the potential for one charger getting feedback from the other rather than the batteries and the bank will not get proper charging. Turning one off with a switch is fine but there will be the chance that both could be turned on at the same time. Chuck
No, that statement isn't correct. There is no such thing as "mismatched" chargers (assuming they are set for the same voltage and battery type). The chargers will never get "feedback" from each other - they will only sense the state of charge of the battery and act accordingly and independently.

If the batteries can take the full output of both chargers, then they will, and both chargers will happily supply them. When the batteries have become charged enough to limit their current input - the absorption phase - then the chargers will start to fold back the current.

At this point, one charger will most likely predominate and the other will mostly shut down. This is no problem because the current going to the battery will be less than that which can be supplied by both chargers. Essentially, you will be running on only one charger at this time, but the other one isn't hurting anything.

And the largest charger isn't necessarily the one that will predominate. That decision will be made by the voltage sensing circuit and internal programming of each charger.

Having two chargers is no different than having a wind gen and solar running at the same time - both will add during bulk and one will predominate during absorption.

There is no problem with running two chargers at the same time - on purpose or accidentally.

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Old 25-12-2011, 19:26   #39
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Re: Proper fusing of various charging sources

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Originally Posted by hellosailor View Post
Mark, i wouldn't call a zap stop (a diode) one-time protection. Yes, it is meant for short interval spikes and yes, continual loads can overheat it and blow it out. But if you don't blow it out, it can and will function for many thousands of events.
You may be correct about that. My only indirect experience with two of them was that they were one-time use (but they did do their job and protected the alternator). I still think it is better to just wire the system to avoid the risk rather than try to mitigate the risk.

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Old 25-12-2011, 19:57   #40
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Re: Proper fusing of various charging sources

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- - So you now consider adding over-current protection at the source end of power cables to protect them from fire should an electrical short develop in the source itself and excessive power flow from a different source to the failed source device.
You mean as per?
Quote:
Originally Posted by R_C View Post
The attached crude sketch
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Old 25-12-2011, 20:31   #41
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Re: Proper fusing of various charging sources

May be of interest Fusing the Battery Cable
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Old 25-12-2011, 21:30   #42
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Re: Proper fusing of various charging sources

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You mean as per?
Yes, the sketch in R-C's post has the "fuses" protecting each "source's" feed wire. Should a source develop a short/fault power flowing back up the line to the source from an alternate source will be shut down by the fuse.
- - In the ancient days the batteries were connected to the power panel battery switch and the alternator output also connected directly or through a diode splitter to multiple battery banks. We never thought about the alternator developing a dead short and then the battery might be able to pump all its power through the alternator feed wire starting a fire.
- - Same with engine starters and its cable to the battery(s). It was not all that uncommon for the starter cable to burst into flames when the starter solenoid stuck closed. I've seen 3 boats that had that happen. Adding the fuse to the cable from the battery positive terminal stopped that problem - as per your excellent link in post #41.
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