Can someone please explain to me the difference between a West Marine battery combiner and a battery isolator - maybe the pros and cons of both? I'm trying to figure out how to wire a Xantrex multi-stage alternator regulator and a West Marine battery combiner . . . I think. The instruction for the installation of the regulator has some real specific safety things to say about using their regulator with an "isolator." I'm trying to figure out if what they say also applies to the WM combiner. Because the combiner instructions and schematics seem to contradict what Xantrex says about isolators. Any help appreciated.
WM Bat Combiner vs Isolator
- Thread starter Morrie
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Don't use isolators.
An isolator uses a pair of semiconductor diodes to prevent two batteries from discharging into each other. The problem is that silicon diodes have a significant (>0.6 volt) voltage drop across them while they are conducting. This poses a problem for the smart regulators because they sense the voltage to decide on the state of the charge, in other words the charger may see 14.2 volts at its terminals while in fact there is less than 13.6 volts at the battery. That is why many regulators state that you should run a separate battery voltage sense line to the battery terminal when using an isolator. On the other hand, a combiner is basically a voltage sensitive relay that recognizes a rise in the battery voltage as it is being charged and physically connects the two batteries directly in parallel while charging, and releases them when the charging stops. The regulator then sees the actual battery voltage. This is now recognized as a preferable way to charge multiple banks. There are now many combiners on the market. They are very simple to connect. A similar device is the Xantrex Echo charger. It is in effect an electronic combiner, but limits the maximum current to the secondary battery to about 10 amps. It is useful for keeping a starter battery topped up. A combiner is real easy to connect. There are basically three wires: a ground and a pair of wires that go to the batteries. You connect the alternator to one battery (the primary), and simply wire the combiner across the banks. Some combiners require you to connect a specific wire to the primary bank, others don't care. I've seen arguments both ways as to whether the primary battery should be the starter or the house bank - I have settled for the house bank.
An isolator uses a pair of semiconductor diodes to prevent two batteries from discharging into each other. The problem is that silicon diodes have a significant (>0.6 volt) voltage drop across them while they are conducting. This poses a problem for the smart regulators because they sense the voltage to decide on the state of the charge, in other words the charger may see 14.2 volts at its terminals while in fact there is less than 13.6 volts at the battery. That is why many regulators state that you should run a separate battery voltage sense line to the battery terminal when using an isolator. On the other hand, a combiner is basically a voltage sensitive relay that recognizes a rise in the battery voltage as it is being charged and physically connects the two batteries directly in parallel while charging, and releases them when the charging stops. The regulator then sees the actual battery voltage. This is now recognized as a preferable way to charge multiple banks. There are now many combiners on the market. They are very simple to connect. A similar device is the Xantrex Echo charger. It is in effect an electronic combiner, but limits the maximum current to the secondary battery to about 10 amps. It is useful for keeping a starter battery topped up. A combiner is real easy to connect. There are basically three wires: a ground and a pair of wires that go to the batteries. You connect the alternator to one battery (the primary), and simply wire the combiner across the banks. Some combiners require you to connect a specific wire to the primary bank, others don't care. I've seen arguments both ways as to whether the primary battery should be the starter or the house bank - I have settled for the house bank.
Relay vs Diode
A combiner is simply a relay that closes and interconnects the two batteries/battery banks if voltage across one of them rises to charging level. If the voltage across both is less than charging level, the relay opens and isolates them to prevent one battery or its loads from discharging the other. The disadvantage of a relay is that it's a mechanical device and can wear out. An isolator consists of a diode in series with each battery or battery bank that only allows current in the charging direction, preventing the discharge of one battery/battery bank to charge the other or power its loads. The disadvantage of an isolator is that the diode has a voltage drop across it that reduces the charging voltage the battery sees.
A combiner is simply a relay that closes and interconnects the two batteries/battery banks if voltage across one of them rises to charging level. If the voltage across both is less than charging level, the relay opens and isolates them to prevent one battery or its loads from discharging the other. The disadvantage of a relay is that it's a mechanical device and can wear out. An isolator consists of a diode in series with each battery or battery bank that only allows current in the charging direction, preventing the discharge of one battery/battery bank to charge the other or power its loads. The disadvantage of an isolator is that the diode has a voltage drop across it that reduces the charging voltage the battery sees.
Combiner or Echo Charge, Diodes NO!
Derek wrote: "I've seen arguments both ways as to whether the primary battery should be the starter or the house bank - I have settled for the house bank." I must admit I've never seen that argument, except for once with a fellow C34 sailor. Once I explained it to him, he understood. He'd thought that the start bank needed the juice first. That's just not true. It should always be the house bank. For two reasons: one, the instructions say so, and second they explain why. The start bank almost never gets depleted since it only takes a few amp hours to start an engine. The house bank is always down, since it's been used and needs more energy. Why run power though the start bank to the house bank, when you need the amps in the house bank first? The combiner wiring is also smaller than the bank wiring. House through combiner to start bank. But we haven't answered Morrie's original question yet. Morrie: think of it this way - the regulator for the alternator only determines the output amount of the alternator, which is the charging method to your battery banks. Think of it as INPUT to the batteries. The combiner takes the place of your old 1-2-B switch. Instead of manually switching to Both to have the alternator charge both batteries, the combiner does it for you. This assumes that you have "standard" wiring where the alternator output goes to the C post of the switch. However, if you read the combiner instructions, you'll need to either rewire your alternator output to the house bank on your 1-2-B switch OR wire it directly to your house bank positive. This is not the forum to rewrite the instructions that came with the combiner. Read them again and you'll see what I mean. Any questions, let me know. Stu
Derek wrote: "I've seen arguments both ways as to whether the primary battery should be the starter or the house bank - I have settled for the house bank." I must admit I've never seen that argument, except for once with a fellow C34 sailor. Once I explained it to him, he understood. He'd thought that the start bank needed the juice first. That's just not true. It should always be the house bank. For two reasons: one, the instructions say so, and second they explain why. The start bank almost never gets depleted since it only takes a few amp hours to start an engine. The house bank is always down, since it's been used and needs more energy. Why run power though the start bank to the house bank, when you need the amps in the house bank first? The combiner wiring is also smaller than the bank wiring. House through combiner to start bank. But we haven't answered Morrie's original question yet. Morrie: think of it this way - the regulator for the alternator only determines the output amount of the alternator, which is the charging method to your battery banks. Think of it as INPUT to the batteries. The combiner takes the place of your old 1-2-B switch. Instead of manually switching to Both to have the alternator charge both batteries, the combiner does it for you. This assumes that you have "standard" wiring where the alternator output goes to the C post of the switch. However, if you read the combiner instructions, you'll need to either rewire your alternator output to the house bank on your 1-2-B switch OR wire it directly to your house bank positive. This is not the forum to rewrite the instructions that came with the combiner. Read them again and you'll see what I mean. Any questions, let me know. Stu
Stu...
The counter argument (which I do not agree with) came from BEP Marine (New Zealand) who make a line of combiners. In their manual they state that the alternator should be connected to the starter battery because it is crucial to maintain a high state of charge there before the current is shared to the house bank. I talked to them about it and they were adamant that this is the way it should be. I agree with you that it makes much more sense to connect to the house bank, for all the reasons you give, and that's the way I have mine wired (with a BEP combiner).
The counter argument (which I do not agree with) came from BEP Marine (New Zealand) who make a line of combiners. In their manual they state that the alternator should be connected to the starter battery because it is crucial to maintain a high state of charge there before the current is shared to the house bank. I talked to them about it and they were adamant that this is the way it should be. I agree with you that it makes much more sense to connect to the house bank, for all the reasons you give, and that's the way I have mine wired (with a BEP combiner).
Thanks a bunch
OK, I got it! I had read both sets of instructions about 5 times but I still couldn't quite grok it. I was missing some basic knowledge that you guys made very clear. Thanks! My next dilema is to figure out what solar controller to use and how to plug it into this system. Any suggestions?
OK, I got it! I had read both sets of instructions about 5 times but I still couldn't quite grok it. I was missing some basic knowledge that you guys made very clear. Thanks! My next dilema is to figure out what solar controller to use and how to plug it into this system. Any suggestions?
Solar
Morrie Depends on how large an array you are planning to install. If the output of the panel is less than 1 1/2% of the amp hour capacity of your bank, you needn't install a controller. I've wired our 11 watt solar panel directly to the PDP of the house bank and it'll, through the combiner, take care of both banks. The sizing was based on only to take care of the inherent daily loss (self discharge) of the wet-cell banks, as I don't leave my boat plugged in when I'm not on board. Good information is available at West Marine Advisors and Jack Rabbit Marine on line. Stu
Morrie Depends on how large an array you are planning to install. If the output of the panel is less than 1 1/2% of the amp hour capacity of your bank, you needn't install a controller. I've wired our 11 watt solar panel directly to the PDP of the house bank and it'll, through the combiner, take care of both banks. The sizing was based on only to take care of the inherent daily loss (self discharge) of the wet-cell banks, as I don't leave my boat plugged in when I'm not on board. Good information is available at West Marine Advisors and Jack Rabbit Marine on line. Stu
Engine Battery First
I agree with BEP. Of course the engine battery must have priority. You are in bigger trouble if you cannot start the engine than if the house bank is down, so get it up first. Also, the engine bank will very quickly come up above 13.8 volts which is the cut in point of the voltage sensing circuit of the combiner. Remember also that anchor windlasses and bow thrusters are mostly run off the engine battery so it may not be true to say it is always well up.
I agree with BEP. Of course the engine battery must have priority. You are in bigger trouble if you cannot start the engine than if the house bank is down, so get it up first. Also, the engine bank will very quickly come up above 13.8 volts which is the cut in point of the voltage sensing circuit of the combiner. Remember also that anchor windlasses and bow thrusters are mostly run off the engine battery so it may not be true to say it is always well up.
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