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Old 21-01-2020, 16:46   #1
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Two engines - one ACR or two?

I have a catamaran with two main engines. Currently it seems they each have their own starter battery, but they are wired together (so not really each their own ...). There is one Blue Seas ACR that connects them to the house bank.


Is this optimal or should I split them and have a second ACR? And maybe a third ACR or combiner switch between the two starter batteries?
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Old 21-01-2020, 17:17   #2
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Re: Two engines - one ACR or two?

guess what you call an ACR is what i call a VSR (voltage sensitive relay) ?

on our cat, we have two starting batteries and two VSR's - on on each battery. 2 independent systems.

there is one issue with our set up that could be improved, in that we could not start the port engine with the stb battery (or vice versa). if have to do this would need to physically move a battery. not the end of the world, but could be if drifting towards the rocks...

cheers,
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Old 22-01-2020, 15:30   #3
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Re: Two engines - one ACR or two?

Quote:
Originally Posted by chrisr View Post
guess what you call an ACR is what i call a VSR (voltage sensitive relay) ?

on our cat, we have two starting batteries and two VSR's - on on each battery. 2 independent systems.

there is one issue with our set up that could be improved, in that we could not start the port engine with the stb battery (or vice versa). if have to do this would need to physically move a battery. not the end of the world, but could be if drifting towards the rocks...

cheers,
Seems like it would be fairly easy for you to wire them together with a manual switch on the positive. Start whichever engine starts, then close the switch and start the other. Then open the switch and let the battery charge just from the appropriate engine.

This is the specific piece of hardware I have. Probably the same as a VSR.

https://www.bluesea.com/products/761...12_24V_DC_120A
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Old 22-01-2020, 15:41   #4
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Re: Two engines - one ACR or two?

On my boat, I've got 2 engines, a generator and 3 battery banks. We'll call the banks "S1", "S2", and "House". Each engine has a 1-2-both-off switch, as does the generator. 1 and 2 on these switches correspond to batteries S1 and S2. Normal positions for the switches are port engine on 1, stbd and generator on 2 (which has them share a battery). House is separate with just an on/off switch.

For charging, there's a 3 bank charger for charging from shore power and generator. This feeds all 3 banks separately. There's also an ACR for each engine with an interlock to the ignition keys (ACR only enabled when key on). Those ACRs connect the engines to the house bank for charging underway. But the ACRs are disabled when the respective engine is turned off, that way batteries charge separately when on shore power, etc.

Each engine (and the generator) in my setup has 2 sources of starting power available just in case.
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Old 23-01-2020, 10:13   #5
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Re: Two engines - one ACR or two?

How about old school jumper cables?
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Old 23-01-2020, 11:56   #6
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Re: Two engines - one ACR or two?

Quote:
Originally Posted by LoudMusic View Post
I have a catamaran with two main engines. Currently it seems they each have their own starter battery, but they are wired together (so not really each their own ...). There is one Blue Seas ACR that connects them to the house bank.


Is this optimal or should I split them and have a second ACR? And maybe a third ACR or combiner switch between the two starter batteries?
I would isolate the starter batteries. and keep a pair of jumper cables or better yet put alligator clamps on the existing cables. High amp switches suck. Inevitably someone turns then under load and carbons the points.
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Old 23-01-2020, 12:09   #7
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Re: Two engines - one ACR or two?

Two separate systems with the option to link. Do it with their fuel as well. Jumper cables and a portable transfer pump do just fine, because you will only link them when something is wrong.

Consider a link for the house batteries as well. Then you've really got redundancy for bad fuel, bad battery, hard starting engine, and blown alternator.

Had this come into play recently. My starter battery for the main engine was acting weak. I got a replacement, but had it just sitting in the engine room. Slow me, the engine was not sarting too well, so I linked the main engine starter battery with the genset starter battery, using jumper cables. Fine. Really slow me, I still didn't replace the battery. Very cold morning (relative term, below 40 F, this is Florida). Engine would not start with both. Moved the jumper cables to the house bank, and that sucker started on the first try. Replaced the battery, and life is back to normal.
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Old 23-01-2020, 16:48   #8
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Re: Two engines - one ACR or two?

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How about old school jumper cables?
i just measured it. on our boat, to use jumper cables to connect the port battery to the starboard engine, the cables would need to be 9m long.

not sure if this is feasible ?

cheers,
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Old 23-01-2020, 19:04   #9
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Re: Two engines - one ACR or two?

I have just rewired our catamaran as it had a strange setup, and so have given the configuration a lot of thought before deciding on a better setup.

We have a start battery for each engine. Each of the start batteries is connected via a VSR to the positive bus bar. Each VCR has a bypass switch, normally off. The house bank is connected to the bus bar via a normally on isolator switch.

The beauty of this arrangement is that either engine can be started from either start battery or the house bank or all. The electrical system can run off either the house bank (normal operation) or if required or one or both of the start batteries. Each alternator will normally charge its own start battery then automatically charge the house bank once the start battery is fully charged. But each alternator can be switched to charge the other start battery and/or the house bank.
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Old 24-01-2020, 05:26   #10
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Re: Two engines - one ACR or two?

Why would you need two start batteries, there is no need to start both engines simultaneously? Connect both engines to one start battery, add the spare battery in parallel with the house and charge the house battery with a single 200 amp Combiner.
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Old 24-01-2020, 06:14   #11
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Re: Two engines - one ACR or two?

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Why would you need two start batteries, there is no need to start both engines simultaneously?
For a lot of boats, I'd agree, 1 start battery is fine. But on a cat, I wouldn't want to normally pull cranking current over a long cable run all the way across the boat. A starter battery on each side is preferred in that situation, I think.
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Old 24-01-2020, 09:03   #12
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Re: Two engines - one ACR or two?

Here's a thirty footer - gives you 6 inches to spare.

https://www.amazon.com/OFF-ROAD-BOOS...%2C329&sr=8-19
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Old 24-01-2020, 10:49   #13
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Re: Two engines - one ACR or two?

I have a genset and 2 propulsion engines. I start main engines from 800 amp house bank. Genset has it's own battery and alternator. If a problem pops up I can separate the house bank quickly into two 400 amp banks. I have a heavy cable with a breaker that I can power from either of the 400amp banks that will reach both engine starters and the genset. With this set up I can get 12 volts to anywhere in the engine room on very short notice. I've used it twice. Once when a starter solinoid failed while starting engines to exit a lock. Once when the genset battery failed. I have tested starting a main engine with 1/2 of the house bank at 11.8 volts and it spun it right over.
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Old 24-01-2020, 22:06   #14
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Re: Two engines - one ACR or two?

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Originally Posted by YANDINA View Post
Why would you need two start batteries, there is no need to start both engines simultaneously? Connect both engines to one start battery, add the spare battery in parallel with the house and charge the house battery with a single 200 amp Combiner.
I only have two start batteries because that is the way that it was originally set up. I think a single start battery isolated from the house bank would be fine. It will easily start both engines. As for the longer wiring, both batteries are side by side.
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Old 25-01-2020, 05:43   #15
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Re: Two engines - one ACR or two?

"I only have two start batteries because that is the way that it was originally set up. I think a single start battery isolated from the house bank would be fine. It will easily start both engines."

It will easily start both engines as long as it does not weaken or fail. When it does, you will not be able to start either. Consider keeping them separate, and charged by separate alternators, as your Plan B for a failure somewhere in your battery/charging system. It's a reasonably expected event, and having a Plan B surely beats sitting outside port wondering how you're going to get in.

All of us rely on cars that have no redundancy in this area. Some of us carry jumper cables. All of us have turned the key and had nothing happen. Getting a jump-off in a parking lot is far easier than getting one from another boat, and our systems are not as reliable as those in cars.
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