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Old 10-10-2016, 09:27 PM   #1
City: Huntington Beach, CA
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Battery Isolator

I have twin Perkins 4-236 in my boat. I use one 4D starting battery to start both engines. This battery is charged by the port engine. The starboard engine charges the house bank. I have a battery switch that is wired to put all batteries on line for starting if needed. When all batteries are on line both alternators are charging all the batteries. I have been running with all batteries on line after starting. Yesterday I found that the alternator on the port engine was very hot when running. All batteries were on line. I think I blew a diode. I wonder since both alts are charging and not isolated could I be putting a strain on the alternators?

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Old 10-10-2016, 10:59 PM   #2
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Usually not a good idea to connect two alternators together. Tha main reason being that one regulator with "argue" with the other. This can cause several problems including only one alternator doing all the work. This may be why only one of yours was hot to the touch.
I would try leaving the two systems separated for a while to be sure all is well with each system.

You should not move your 1,2,both switch while the engine is running, that will pop a diode. Some switches have a field disconnect to allow this but it can't disconnect the fields from two alternators.

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Old 10-10-2016, 11:03 PM   #3
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Unless you have an external 3 stage regulator, the alternators are designed to handle the load and moderately recharge the batteries. Would ask an alternator repair facility to trouble shoot the alternator. If the regulator became faulty, it may have had the alternator running at too high an amperage output which over heated it.

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I want to spend some time, Not come and go in a heated rush.....
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Old 10-11-2016, 06:26 AM   #4
City: Seaford Va on Poquoson River, VA
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I have been running my Delco 12SI alternators combined outputs for years with no troubles at all. It helps unload the alternator charging the 2 house batteries while the other loafs charging a single start battery. I put a continuous duty relay between the banks with a manual switch run off the fuel pump relay signaled from alternator the charges the single start battery.

I know it works as the amp gauge on one side falls, and the amp gauge on the other side rises when joined.

one time, I burnt a belt since one alternator was charging 2 house batteries putting out 60 AMPS and it was too loose. Letting both share the load is good idea, at least for ME. Whether it works for others, I can not say. Everyone has their own opinion about things.
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Old 10-11-2016, 09:20 AM   #5
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AmplePower relates some (but not all) problems with connecting 2 alternators together.

Two Engine/Alternator System
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