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Old 08-04-2019, 11:08 AM   #1
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continuous duty 100-150 amp relay to join battery banks 1 and 2

Some time ago, installed a continuous duty 150 amp relay to join battery banks 1 and 2
With 2 engines and 2 alternators, its been working good, the load on alt 1 drops in half and alt 2 picks up the difference when I throw switch on. This is clearly visible on the ammeters connected to alternators 1 and 2. Alternators are 12SI Delco.

I was told by some it would not work! That they would fight each other, and one would loaf.
Without the relay, depleted house battery bank 2 works alternator 2 really hard while alternator 1 just charges the starter bank 1 and loafs almost unloaded. The relay is extending the life of alternator 2. One time before I had this relay, alternator 2 belt burned up due to overloading and alternator got pretty hot.

The other advantage (if battery bank 2 is not depleted), the relay boosts the starting power for the engine starters, as they then have both battery banks 1 and 2 to draw from. I pretty much leave the helm switch on all the time, and you know its working because it makes an audible click when turning on.

The combining relay's on switch at helm was wired to the fuel pump of engine #1. I have since realized, I could use 2 diodes in the incoming power to the combining relay helm switch, so that either engine 1 or engine 2 could be on and the other engine off and the relay can come on. Right now engine 1 has to be running for combining relay to work, so I will probably make that mod soon. The diodes have to be big enough ones to handle the current for the relay coil. End of each diode would connect to the fuel pump or ignition on of each engine and other ends joined together into power in at helm switch for the relay. You have to get the diode facing the right way, think of it as a one way valve for electricity.
Power flows to switch and blocked if was coming from switch, that way turning on one engine ignition wont activate (backfeed) power to other engines ignition circuits.

When ignition is off, the relay is off, and the banks are not combined.

And I cant say if it would work with different kinds of alternators.
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Old 08-04-2019, 11:57 AM   #2
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I did what you describing with a continuous duty relay to tie 2 battery banks together when the engine was running. I ran the wire to the ignition switch with another option. Bringing the wire to the helm and running it through a single pole double throw center off switch would allow you to select either engine to trigger the relay or have an off position if you didn't want to combine them.

Ted
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Old 08-04-2019, 12:10 PM   #3
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I did what you describing with a continuous duty relay to tie 2 battery banks together when the engine was running. I ran the wire to the ignition switch with another option. Bringing the wire to the helm and running it through a single pole double throw center off switch would allow you to select either engine to trigger the relay or have an off position if you didn't want to combine them.

Ted
Yes, that would work I think. You would have to move switch left or right depending which engine was running, my way its more automated.
I already have big diodes from a busted inverter I can use and am using the Carling breaker switch with white handle in the dash. My dash switches are a long vertical row of Carling white handled toggle breaker switches. I had room to add 2 more at the bottom. Must be at least 14 there.

One added switch I use to power on two Rule 3700 at same time, I used 2 cube relay 40 amp to do that and isolated each to also using separate bilge level pump switches. That way I can turn both on together but each turns on separately by its associated bilge level switch.

The other controls this relay.
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Old 08-06-2019, 03:46 PM   #4
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Got it done today so that either engine coming on will power the relay.
Created album of how I did it.
Power from each engine ignition wires goes into power diodes with white bar mark facing towards item you desire to power up.
Other ends of both diodes joined as one to power the coil of the relay.
No power can backfeed, the diodes prevent this. Diodes act like one way valves for DC current.
Each diode drops the forward voltage by 0.4 vdc, which is meaningless for the relay coil.

I do think people who have trouble soldering, the metal has to be super clean, if solder wont flow, its either not hot enough, or dirty. I use electrical solder with rosen flux, but if the metal wont take solder, I mechanically scrape it, and will use Oatey water based plumbing flux. Then clean it off afterwards with rubbing alcohol or water. Never failed me yet.

https://photos.app.goo.gl/EuZGWvccuWidYJNBA

These diodes are good sized, likely 10 amp capable at least.
And that wire is over 50 years old, salvaged from another 60's model Eggharbor that was crushed, and like new. they used this wire for the overhead lighting in those boats and a few other things. The only old wires that are failing are the old SO rubber coated, the insulation beginning to crack, and I have one wire run left to replace, goes to an aft bilge pump.
Diodes I salvaged from a busted 3000 watt inverter, but they are cheap to buy.
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Old 08-07-2019, 05:42 AM   #5
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For folks that can be bothered with diodes, a simple solution is a marine grade key starter switch that like a car that has an ACC terminal.

Simply power a 200A cont duty relay (about $40) from the ACC terminal .

This is how its done on millions of RV for a half century , though most use a 60-75A solenoid for $18. or so.
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Old 08-07-2019, 06:31 AM   #6
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You cant use a starter relay as its not continuous duty, it will get super hot if its active a while. I bought my relay off Amazon, a golf cart relay may be suitable. I use a carling white handle on- off breaker switch in series to give me a manual off and on. The power source is the ignition circuit of each engine joined together with the diodes. The way I do it, its automatic on - off, no key turn needed. It can be left set to on all the time. The diodes just let it activate regardless of which engine is running. Larger numbers of battery banks could be joined by using more relays. I could connect my generator battery that way too.

I looked into ACR but honestly dont need to spend money on those to get same or better functionality, like no starter boosting with more banks by using a combining relay that is on when cranking. An ACR wont join together banks until voltage exceeds a certain value developed by an alternator.

And you dont need a huge interconnecting battery bank wire, I used 2 gauge?, about 4 to 5 feet fit my space, (whatever it was big enough and never been a problem) joins the positive poles of the battery banks together through the relay. Its primary purpose is sharing alternator . My alternators max at 80 amps each. Worst I ever saw, one was putting out 60 amps and burnt up a belt before I did this.

Whatever switching arrangement you use, you want it OFF when both engines are off, without you having to remember to turn it off, so automatic. Otherwise the banks will stay connected and you could drain them both to zero.

The way I have mine setup, I dont have to interact with the switch at all. I can ignore it completely, of course it has to be set to 'on' or it wont do anything. But it can stay on all the time forever even.
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Old 08-07-2019, 07:26 AM   #7
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One should use interconnecting cables capable of handling max amps in a short ( battery dead short resistance) if you don't provide overcurrent protection in that cable.


It was included in the new ABYC suggestions...cause quite a stir about the new battery terminal fuses.
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Old 08-07-2019, 01:26 PM   #8
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Starter solenoids are not for cont duty.


A genuine marine Cole Hersey 200A unit can be had at Wallmart.

Cole Hersee 24213 12V 200A Continuous Solenoid

$37.99 Pick up in store ,free shipping, , plus local taxes
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Old 08-07-2019, 01:39 PM   #9
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Starter solenoids are not for cont duty.


A genuine marine Cole Hersey 200A unit can be had at Wallmart.

Cole Hersee 24213 12V 200A Continuous Solenoid

$37.99 Pick up in store ,free shipping, , plus local taxes
This is the one I bought $15, but in 2016, I paid $10, and has been perfect for this purpose.
!50 amp surge. If my alternators were more powerful, I might have gotten a bigger one.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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Purchased 1 time
Last purchased on September 20, 2016
Its been a few years too. If you get a solenoid, make sure actually is continuous duty, some still have a duty cycle, so they are not really continuous..
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Old 08-12-2019, 06:32 AM   #10
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"If you get a solenoid, make sure actually is continuous duty, some still have a duty cycle, so they are not really continuous.. "

and make sure it has marine grade contacts , usually silver plated for the corrosive sea air environment.
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Old 08-12-2019, 10:08 AM   #11
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"If you get a solenoid, make sure actually is continuous duty, some still have a duty cycle, so they are not really continuous.. "

and make sure it has marine grade contacts , usually silver plated for the corrosive sea air environment.
Many relays do already have that as the point contact area is smallish. And it makes those points very long lived.

Every solenoid I have taken apart, it's been large copper washers and copper bolts. They are meant to take large currents.
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Old 08-12-2019, 12:49 PM   #12
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Many relays do already have that as the point contact area is smallish. And it makes those points very long lived.

Every solenoid I have taken apart, it's been large copper washers and copper bolts. They are meant to take large currents.
Switches and solenoids are designed to clean their contacts with usage as long as they are used within their specified current range. Not using them is what will allow corrosion to take hold and shorten their lifespan.
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Old 08-13-2019, 05:44 AM   #13
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"Every solenoid I have taken apart, it's been large copper washers and copper bolts. They are meant to take large currents."


Yup, large currents require copper , but have you noticed how most power cords are built? And folks wonder why the ends burn off.
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