Battery Isolators

Does anybody here have a battery isolator installed on their boat with one alternator and two batteries? If so which type do you have? How well does it work? How long have you had it? How often does it get used? Any other comments pro or con are welcome.

I am getting ready to install a second battery and am thinking about installing an isolator.

Thanks,

Durwood

Re: Battery Isolators

I was about to post the same question. I'm looking at this battery switch on West Marine's site:

WM Model #: 10065969
Manuf. Part #: 701S

Is it as simple as wiring this switch in-line and then pig-tailing to each battery from there? Are there other implications I'm missing.

Lil help would be appreciated.

Re: Battery Isolators

A few more minutes of searching found that Blue Sea Systems' "Add-a-battery" system appears to be the way to go. West Marine has them and you can look at their manuals which have wiring diagrams. link http://www.westmarine.com/webapp/wc...Primary Search/mode matchallpartial/0/0?N=377 710&Ne=0&Ntt=blue sea add-a-battery&Ntk=Primary Search&Ntx=mode matchallpartial&Nao=0&Ns=0&keyword=blue sea add-a-battery&isLTokenURL=true&storeNum=5002&subdeptNum=9&classNum=12106

Re: Battery Isolators

Ask yourself first, "why am I adding a second battery?" What will the second battery be powering if anything. Is it just a spare? These are important questions and an isolator may not be what you really need. An isolator is just that -- it isolates the two batteries but allows the alternator to charge both of them. The issue with them is there is a voltage drop across them. They also don't allow starting the engine from the second battery if the starting battery is dead (unless you have jumper cables with you). Isolators are not something you turn on and off -- they operate anytime the engine is running. A better solution (there are two of them) are an ACR (automatic charge relay) or a dual battery switch. An ACR allows the starting battery to be the default battery and always gets charged first. When it is fully charged the ACR switches to the second battery. Again, unless the ACR has a COMBINE function that ties the two batteries together, you cannot start the engine from the second battery. A dual battery switch is the simplest, easiest to install, and least expensive, as well as being the most versatile solutin. It is a heavy duty switch with four positions. OFF = disconnects both batteries so nothing can drain them. BAT 1 = the starting battery powers everything on the boat and only it is being charged when the engine is running. BAT 2 = the second battery powers everything on the boat including the engine starter and only it is being charged when the engine is running. BOTH = both batteries power everything on the boat and both are being charged when the engine is running.

Re: Battery Isolators

I have a battery isolator and love it. Been on the boat since 1980 and it works perfect to keep both batteries charged.

It really depends on your boat if a battery isolator is the best way to go.
If you have an outboard or a one wire alternator then a ACR or VCR is a better way to go.

If you have a I/O with a three wire alternator then you can not do better than a battery isolator. There is no relays to chatter or contacts to burn up and not make good contact. Also their is no voltage drop to the battery. You can also wire it with a switch if you think you might run down your starting battery or have a single jumper cable long enough to go from the positive wire on one battery to the positive wire on the other battery.
In my case the stuff that came with the boat is on battery 1. So the stuff on battery one normally only used when the motor is running and battery 1 very unlikely to be run down.

Second battery has all the add on gear. VHF Radio, Loran C, GPS, Fish finder, power outlet for charger or blower to inflate raft or portable spot light.

The thing I really like is you do not need a switch and do not have to play the switch game.
Put on one to start, then change to both to charge both while under way, then switch to 2 to run off of battery 2 while stopped, then back to one to start, back to both to again charge both.

Witn an isolator all you do is turn your key and start off battery one. Both batteries are charged as soon as the engine is running.

Re: Battery Isolators

This is why I asked what he intends to use the second battery for. Just like shoes and styles, one size/style does not fit all. If it is a backup for the start battery, then an isolator does him no good unless he's carrying jumper cables. If it's purpose is to power other stuff then an isolator can work if he ignores the starting issue. I do agree the isolator is the simplest from a purely operational standpoint. A switch is the most versatile. Everything else falls in between so what you really need depends on what problem(s) you are attempting to solve or prevent by adding the second battery. Actually, the cheapest solution to the starting issue is to just carry a charged second battery and jumper cables or a jump start unit.

Re: Battery Isolators

Boatist said:

I have a battery isolator and love it. Been on the boat since 1980 and it works perfect to keep both batteries charged.

It really depends on your boat if a battery isolator is the best way to go.
If you have an outboard or a one wire alternator then a ACR or VCR might be a better way to go.

If you have a I/O with a three wire alternator then you can not do better than a battery isolator. There is no relays to chatter or contacts to burn up and not make good contact. Also their is no voltage drop to the battery.

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With a diode isolator you DO have a voltage drop to the battery across the diodes. Most ACRS are solid state these days so there is no relay. As far as chatter goes, they have hysteresis built in so that the cut in point and the cutout point are far away from each other. There is never chatter. Need to get the facts straight.

Basically, don't use the old technology of a diode isolator.

Re: Battery Isolators

I thought I posted a reply earlier today but I guess it did not go through. I am installing the second battery to run the electronics mainly and secondly as a back up to my starting battery if needed. I am installing switches so I can connect the two or start on the second one by itself if needed. I just wanted the isolator to charge both batteries at the same time but not have them connected to one another.

Durwood

Re: Battery Isolators

turbinedoctor said:

I thought I posted a reply earlier today but I guess it did not go through. I am installing the second battery to run the electronics mainly and secondly as a back up to my starting battery if needed. I am installing switches so I can connect the two or start on the second one by itself if needed. I just wanted the isolator to charge both batteries at the same time but not have them connected to one another.

Durwood

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An ACR would be perfect for your application.

Re: Battery Isolators

bruceb58 said:

With a diode isolator you DO have a voltage drop to the battery across the diodes. Most ACRS are solid state these days so there is no relay. As far as chatter goes, they have hysteresis built in so that the cut in point and the cutout point are far away from each other. There is never chatter. Need to get the facts straight.


With a 3 wire alternator the sense input to the regulator comes from the battery so the battery is regulated to what ever voltage the regulator is set at. You could have 10 diodes in line and the battery would still get the same voltage. The alternator it's self would put out a higher voltage until the voltage at the battery reached the voltage the regulator is set at.

With a one wire alternator or an outboard then yes the voltage at the battery will be about .7 volts less than the regulator is set at because it voltage sense feed back come form before the isolator diode.

I was helping a man with a with a ACR or VSR. It basically waited until the starting battery reached a certain voltage then picked a relay to charge the second battery. Second battery was a larger deep cycle and as soon as it started to charge the relay would drop back out because the starting battery voltage dropped a lot. When it dropped back out the voltage would rise and the relay would pick again. It sounded like a small buzzer for quite a while. Now the guy had a outboard that only had about 10 amps of output. He finally agreed that his outboard did not really have enough output to charge the large deep cycle battery.

Now this has been back about 10 years. If there all solid state now then it would not buss like that one did.

That the facts and they are accurate.

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Re: Battery Isolators

Boatist said:

With a 3 wire alternator the sense input to the regulator comes from the battery so the battery is regulated to what ever voltage the regulator is set at. You could have 10 diodes in line and the battery would still get the same voltage. The alternator it's self would put out a higher voltage until the voltage at the battery reached the voltage the regulator is set at.

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So...I take it you do that in your boat? So which battery do you put your sense on? So, what happens when you have a fully charged battery that has the sense on it and the other is severely discharged? I will tell you what happens...the other battery will not get charged fully or as fast as it could. Eventually, the deeper discharged battery will get up to the voltage of the fully charged battery, but it will take a long time.

Re: Battery Isolators

bruceb58 said:

So...I take it you do that in your boat? So which battery do you put your sense on? So, what happens when you have a fully charged battery that has the sense on it and the other is severely discharged? I will tell you what happens...the other battery will not get charged fully or as fast as it could. Eventually, the deeper discharged battery will get up to the voltage of the fully charged battery, but it will take a long time.

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The since line is on the starting battery and as soon as I start the engine it reached 14.4 volts very fast. My alternator is a 65 amp.

The deep cycle also reach 14.4 volts at the same time. While the starting battery has very little current going to it the deep cycle will have a lot of current going to it.

The voltage drop a crossed a diode is almost constant at .7 volts. A diode is not like a resistor where the voltage drop changes a lot with higher currents.
My deep cycle charges very fast as it will get 20 to 25 amps in the if it has a big discharge.

On my boat the deep cycle rarely has a deep discharge as I do not have a electric trolling motor. Ever if we are drift fishing from 6 am to 1400 and only start the motor for a short time to go back over the same area a second time your will not see any voltage drop.
I use the same meter to check both batteries with a spring loaded switch to keep it on battery one unless your holding the switch. With the motor running or stopper will see very little change if flip to the deep cycle.
We fish a lot in the ocean so is a 20 minute to 2 hour trip to get out and back in depending where we are fishing.

We usually fish for 7 days weather permitting when we go to the ocean camp ground.
When we get back home I fully charge both batteries thru the same battery isolator with my home 10 amp charger and it will take less than 20 minutes to taper to 0 amps. It will be fully charged long before we get the boat unloaded.

Re: Battery Isolators

Guys I was only asking who has and is using a battery isolator and how well they like it. I think you for your thoughts and comments but I have decided to go with a battery isolator and was wondering if there is a big difference between the makes and models of them, i.e. this one worked great for several years or this one sucked aviod at all cost.

I have a outboard with one wire from the rectifier and it only puts out about 9 amps. I curently have one deep cycle which it charges just fine, as a matter of fact it alone is not enough load since my voltage raises to 16 volts shortly after leaving the dock. I am hoping that a second battery will help to lower this voltage with the extra load.

My main reason for the second battery is a back up in case the first one dies while away from the dock. I am installing switches to isolate them and be able to join them or select battery 2 for starting.

Again, who has a battery isolator and how well do you like it?

Durwood

Re: Battery Isolators

I used the SurePower separator for years on the Four Winns and Larson. Never had to worry about the starting battery draining, and if it did go dead the flip of a switch would have put the device into boost mode. As I recall it was around $50.

Re: Battery Isolators

Turbinedoctor
Normally I would not recommend a battery isolator with a 9 amp outboard. It sounds like your outboard does not have a voltage regulator. The battery isolator diodes will drop about .7 volts so it may bring your voltage down from 16 volts to 15.3. The second battery will also take about half of the current which also should lower the voltage some.

The one concern I have would be if you added a trolling motor and ran down the second battery. In this case your charging system would be putting out max current all the time and could over heat.

In your case a isolator may work very well for you.
The only times I have heard of battery isolators problems is when they were overloaded. Example they got a 50 amp isolator but were charging 2 large batteries and their alternator was 130 amps. The isolator failed.

Isolator usually rated in max current but I do not think they make any that would be damaged by a 9 amp charging system.

The isolator is really just two diodes mounted to a heat sink. Very simple and very little to go wrong. One thing that I would look for is one that has a cover or the connections that can have rubber boots to cover the connections and prevent anything metal from hitting them and shorting them out.

One last question is do you have a separate line for charging and for the starter circuit? If you have only a single positive wire that connects to the battery then to use a battery isolator you will have to rewire so the starter line and charger output are separate.

This will be different for each outboard so before you buy make sure you know how to wire for your motor.

Someone in the outboard forum for your brand motor may be able to help but do not buy until you know how to wire for your outboard.

Re: Battery Isolators

I still don't understand why you just don't get an ACR. No messing with your outboard charging system. Just connect it across the two positives of the batteries and one ground wire. Simplicity!

Re: Battery Isolators

I have had 3 isolators on 3 different applications.... all were whatever cheap brand was on the shelf at autozone or oreily's and all have performed flawlessly.... no failures in 10 years....

Re: Battery Isolators

smokeonthewater said:

I have had 3 isolators on 3 different applications.... all were whatever cheap brand was on the shelf at autozone or oreily's and all have performed flawlessly.... no failures in 10 years....

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Did you happen to read what he is putting this on? He is putting it on an outboard. You going to advise him how he is going to bring out his charging output sperately?

Re: Battery Isolators

yeah, but then he said: "Guys I was only asking who has and is using a battery isolator and how well they like it. I think you for your thoughts and comments but I have decided to go with a battery isolator and was wondering if there is a big difference between the makes and models of them, i.e. this one worked great for several years or this one sucked aviod at all cost" so I gave my experience

With a 10 amp charging system isn't going to make a dent in charging a deep cycle unless he is trolling for 1 hour and cruising for 10 hours but he stated that he didn't want that sort of advice

Re: Battery Isolators

smokeonthewater said:

I have had 3 isolators on 3 different applications.... all were whatever cheap brand was on the shelf at autozone or oreily's and all have performed flawlessly.... no failures in 10 years....

Click to expand...

This is what I was looking for.

I think I can handle hooking up a wire or two.