- The simplest way, if you can remember to do it, is to turn your battery switch to "BOTH" when charging, and turn it back to 1 or 2 when you are finished. This solution is unsatisfactory for those who sometimes forget and then end up with a flat battery from time to time. The Blue Sea 9001e is an example of a 1-2-Both battery switch. If you want to automate the process and make it idiot proof, then you need to pick one of the other options. This 1-2-Both switch is the way most boats come as standard, and the least satisfactory method.
- The best way, if you can manage it, is to have two alternators. This allows independent charging of each bank, and by fitting a combiner switch you get the added feature of a backup alternator for either bank in the event of a failure. This is a technically challenging project which is usually not an option for most installations.
- A hugely popular and successful way is to use a battery combiner such as a Blue Sea ACR ACR stands for Automatic Charge Relay. This is a solenoid which connects the batteries together when they are being charged and separates them when they are being discharged. Blue Sea designed a special Add-A-Battery kit with a special dual bank battery switch and an ACR to totally automate the process.
- The newest way to do this is the one that gets used most often for Lithium Battery installations is the Battery to Battery Charger. This allows a totally different charge profile for each battery type. Take your alternator to whichever battery you decide, and then use the Battery to Battery charger to take a different charge profile to the second battery.
- The old fashioned way was to use a battery isolator, which is a set of diodes which allow the charge to go to each battery but doesn't allow the batteries to connect to each other. One problem is that there is a voltage drop across the isolator which means heat is generated and your precious energy is wasted. It also means that you can only use an externally regulated alternator so that it can sense the voltage downstream of the isolator. Isolators have had a new lease of life lately with the availability of FET Isolators. These do the same job with lower losses, so reducing heat build-up and improving reliability. At PKYS we now stock a range of these Victron ArgoFet Isolators
6 Comments
Liang Wang
Hi, my house and starter banks are wired to the outputs of a Cristec isolator. I also charge the house bank from a MPPT solar controller. My question is, can I add a combiner between two banks so to make sure the starter is charged by solar as well? Is there any side effect having both isolator and combiner between the two banks? Thanks!
Peter Kennedy
In this arrangement the isolator is surplus to requirements. It has cooling fins on it because it generates heat, which is wasted energy. If you got rid of it the ACR would distribute the charge to a second battery with no energy loss.
Chris
Current situation: -Outboard with charging system only large enough to charge one battery. - Want to charge each battery with outboards charging system, but don't want to move wires or turn switches. - 2 battery switch installed from bat 1 to bat 2 or both. Should I use an isolator, separator, or something else? Do you have a recommended manufacturer for whatever would work best?
John Murrell
Starting Batteries & Domestic Batteries are normally different types. The starter battery is designed for high currents but not to be discharges and the domestic battery is designed to be discharged and is often a sealed lead acid battery. Since these batteries have different charging characteristics you can't charge them in parallel. If you do you will either end up overcharging and ruining the domestic sealed battery or else if the alternator is set for the characteristics of the domestic battery the starter battery will not charge.
Peter Kennedy
Having an automatic battery combiner works well if the batteries you are combining are similar in size or chemistry. If they are very different from each other it doesnt work so well, and if one is Lithium and the other is a conventional battery the ACR doesn't work at all. For dissimilar batteries the way to do this would be to take the alternator to one of the batteries and use a Battery to Battery charger for the other.
Stuart Scheinberg
I recently purchased a 2 year old Sea Fox boat with a Yamaha 300 outboard. There are two separate battery switches with 1-2-Both. One switch goes to one starting battery, the other switch goes to 2 batteries that run the accessories. This second switch is not set up to charge from the motor at all. What is the best way to set this entire system of 3 batteries to charge from the motor and keep them set up to operate the same. Should I just run a jumper from the terminal on the switch receiving the charge from the motor to the other switch?
Kent Collins
Im working on this myself . Ideally keep a 1.5 maintainer hooked up, however how do you know both batteries are charging? What I did was turn my Perko Switch off. I dont want to charge the battery while all systems are hot including the ignition. So anyways Switch off and charged one battery @ 2 amps for 24 hrs. Then I tested the other battery with a battery tester and it was below 12 volts. So that tells me my Perko switch will not charge both batteries when in the off position. So now I will charge the other battery @ 2 amps for 24hrs. once this is completed I will put a 1.5 amp maintainer to one battery, switch off and then run two small jumper cables to the other battery and run them parallel . This should work great thats how I charge multiple batteries at once anyways. not in a boat
Josef Farrugia
I have a twin engine set up on my boat. Would like to have a starting battery which starts both engines, and a house battery for domestic use. Can I have one alternator charging the start battery and the other alternator charging the house battery ?
Peter Kennedy
Yes you can take one alternator to each battery. Its not a bad arrangement. You can fit a manual combine switch so if one engine or one alternator isnt working both batteries still get charged.
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