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Old 12-06-2020, 06:29 PM   #1
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OMG, shortening the battery cables... Inverter in engine room.

My, new to me boat, came with some really long runs of DC cables, but what do I know?

I had a marine surveyor inspect the boat before buying. the survey basically says, "the electrical systems generally comply with ABYC standards".

Some issues were obvious, some were a bit of a puzzle.

For example the bilge pumps weren't working, bad ground got some action going but still not right, ... They were wired in improperly on the 4 battery bank and only getting 6 volts.

After sorting out the systems a bit to make sure 1, that I generally understood the systems and 2, that the cables were following electrically logical and safe paths and 3, had some confidence the whole thing would not burn down; I decided to run a higher load test.

My microwave was to heat some water using the Xantrex Freedom XC 2000 inverter. The batteries were fully topped up, a bank of 4 Trojan T125's.

The microwave was set to use 1000w of cooking power which means after it's overhead is added it needs just shy of 1200 watts of 120, 10 amps from the inverter.

The microwave ran!

There's always a but though, The battery monitor was showing 188 amps being sucked out of the battery bank, the cables could only get 10.5 volts delivered to the inverter.

That 188 amps is just under the 192 amp input limit of the inverter so I stopped the test fast just after reading the numbers.

I'm skilled enough to be able to guess that the wires were too long, but after down loading the owners manual for the inverter I got a good schooling on inverters and just how bad the installation was botched on this boat.

To start the recommended minimum size battery cables for a 5 foot run are 3/0 to the battery and Chassis ground at 2/0.

WTF? The installed cables, 1/0 at ~20 feet with 10 AWG running to the house bus bar for the chassis ground.

Similarly the starter cable makes about a 50 foot circuit. The bow thruster and windlass have runs way too long also.

If this is anywhere near the norm for a DIY or semi-pro-non-specialist install, it's a wonder more boats don't burn down.

Rant over.

Productive thought follows. To fix this I need to shorten the cables, a lot. That means 1, getting the inverter close to the batteries and 2, moving the batteries around the boat some.

It's a 1977 Ocean Marine 40 foot with a Lehman 120.

So first, I know it's not safe to put an inverter in an engine room with gasoline power but I'm getting the impression that it's ok around diesel power (with a caveat about heat). Is that right?

Second, I'm including a hand drawn 'plan' for your educated comment. This plan only deals with the Start and Aux batteries. It gets the aux battery out of the engine room up under the V-berth floor and uses heavy relays to be able to run the heavy cables direct and use control wires for the run to the helm.

Thanks for your help.

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Old 12-06-2020, 07:38 PM   #2
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In general, I like to have a separate battery for the thruster and windlass. Then you can run heavy (4/0) cables for a short run. Put a separate battery charger there. I donít care if you can get away with a smaller cable for the short run I like the big cables so that voltage is at the maximum that the batteries supply. The extra cost is a one time cost but the benefit is every time you use the thruster or windlass you get better voltage. I would not put the inverter in the engine room and especially above the batteries if they are LA batteries. I am going to Lithium batteries for the house bank but they are pricey. Check every connection for corrosion. I like to put a copper paste on the ends of the cables before the connector goes on. Helps with conductivity and helps prevent corrosion. Then use adhesive lined heat shrink on all the connectors. I always go larger on wiring so that I get the absolute best voltage I can. Cheap in the long run.
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Old 12-06-2020, 08:04 PM   #3
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Why are you worried about a gasoline engine. That Lehman is a diesel.
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Old 12-06-2020, 08:23 PM   #4
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Originally Posted by Russell Clifton View Post
Why are you worried about a gasoline engine. That Lehman is a diesel.
Not worried about gasoline.

Just haven't found a definitive "yes an inverter is ok in a diesel engine room" yet.
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Old 12-06-2020, 08:38 PM   #5
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Heat is a big killer for many inverters, plus battery fumes if too close, and finally soot/oil in the air even though it's not much most of the time


Engine room can be done, but not preferred.
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Old 12-06-2020, 08:43 PM   #6
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Originally Posted by Comodave View Post
In general, I like to have a separate battery for the thruster and windlass. Then you can run heavy (4/0) cables for a short run. Put a separate battery charger there. I donít care if you can get away with a smaller cable for the short run I like the big cables so that voltage is at the maximum that the batteries supply. The extra cost is a one time cost but the benefit is every time you use the thruster or windlass you get better voltage. I would not put the inverter in the engine room and especially above the batteries if they are LA batteries. I am going to Lithium batteries for the house bank but they are pricey. Check every connection for corrosion. I like to put a copper paste on the ends of the cables before the connector goes on. Helps with conductivity and helps prevent corrosion. Then use adhesive lined heat shrink on all the connectors. I always go larger on wiring so that I get the absolute best voltage I can. Cheap in the long run.
The concern that I have heard about putting an inverter above the L.A. batteries is two fold, hydrogen and caustic fumes. The consensus I'm seeing is that both dissipate very quickly with even a little venting. The recommendation is simply to mount the inverter lower.

Mounting low brings up a (code?) concern about having the inverter below waterline.
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Old 12-06-2020, 08:49 PM   #7
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I agree that the ER isn't a desirable location for the inverter.


Another approach to solving the problem would be to up-size the cables. There are lots of calculators for figuring the voltage drop through wires, and you could run that on your setup. 4/0 cable might do the trick, or perhaps even two in parallel. I think it's worth an hour to at least check it out.
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Old 12-06-2020, 08:50 PM   #8
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Not worried about gasoline.

Just haven't found a definitive "yes an inverter is ok in a diesel engine room" yet.
That where our inverter has been for the last 30 years and just had another survey done last week and no problems with it there. We just have to change the chassis ground to 1/0 cable per the ABYC requirements for our inverter.
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Old 12-06-2020, 08:52 PM   #9
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Quote:
Originally Posted by psneeld View Post
Heat is a big killer for many inverters, plus battery fumes if too close, and finally soot/oil in the air even though it's not much most of the time


Engine room can be done, but not preferred.
Yep, all things on a boat are a compromise.

I'm thinking that if I ensure good ventilation, then the engine room (and under V-berth battery is probably a lot less risky, and easier on the equipment.
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Old 12-06-2020, 08:54 PM   #10
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That where our inverter has been for the last 30 years and just had another survey done last week and no problems with it there. We just have to change the chassis ground to 1/0 cable per the ABYC requirements for our inverter.
I like that.
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Old 12-06-2020, 08:58 PM   #11
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I will assume that you do have house batteries separate from the starter and aux batteries.
Moving the Aux battery forward is a good idea (closer to the windlass & Thruster), as log as you can provide Eng. charging capability.
Why a timer switch while you can use a standard switches to activate the Aux battery to run the windlass or Thruster separately when needed (of course still driven by the ignition switch). you timer switch will put the Aux and the Start battery in parallels after 10min and you will loose both batteries if the alternator goes bad.
good luck.

The inverter in the Eng Room should just fine and you can also add ventilation if you heat any concerns.
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Old 12-06-2020, 08:58 PM   #12
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I agree that the ER isn't a desirable location for the inverter.


Another approach to solving the problem would be to up-size the cables. There are lots of calculators for figuring the voltage drop through wires, and you could run that on your setup. 4/0 cable might do the trick, or perhaps even two in parallel. I think it's worth an hour to at least check it out.
I did try 2 calculators and according to both there simply isn't a normal cable size that is big enough.
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Old 12-06-2020, 09:38 PM   #13
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Originally Posted by Comodave View Post
In general, I like to have a separate battery for the thruster and windlass. Then you can run heavy (4/0) cables for a short run. Put a separate battery charger there. I donít care if you can get away with a smaller cable for the short run I like the big cables so that voltage is at the maximum that the batteries supply. The extra cost is a one time cost but the benefit is every time you use the thruster or windlass you get better voltage. I would not put the inverter in the engine room and especially above the batteries if they are LA batteries. I am going to Lithium batteries for the house bank but they are pricey. Check every connection for corrosion. I like to put a copper paste on the ends of the cables before the connector goes on. Helps with conductivity and helps prevent corrosion. Then use adhesive lined heat shrink on all the connectors. I always go larger on wiring so that I get the absolute best voltage I can. Cheap in the long run.
^^^This.

We have 2 group 31 AGM on a standalone charger under the forward berth for the thruster. Short cable runs so max power is drivers to the thruster.

For the house bank, I went with doubled 4/0 cable from the bank to the inverter, and 3/0 to feed the main DC distribution panel.
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Old 12-06-2020, 09:54 PM   #14
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I will assume that you do have house batteries separate from the starter and aux batteries.
Moving the Aux battery forward is a good idea (closer to the windlass & Thruster), as log as you can provide Eng. charging capability.
Why a timer switch while you can use a standard switches to activate the Aux battery to run the windlass or Thruster separately when needed (of course still driven by the ignition switch). you timer switch will put the Aux and the Start battery in parallels after 10min and you will loose both batteries if the alternator goes bad.
good luck.
The length of time idea is good, I may consider a shorter duration.

The idea of the timer is to avoid a problem like what you describe. With the old school, manual switch on 'both' position, there is no automatic protection of the starter battery from overuse.

The time for the 'both' relay, is only there to allow the aux battery some time to 'jump charge' the starter battery.

While 'both' could be used the other way to help the bow thruster that is not the intent.

Your thought there got me thinking and I do think that I will change what I call that relay/switch to 'start assist' or 'jump start' so that other people better understand the intent.
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Old 12-06-2020, 10:03 PM   #15
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Peter, so nothing is charging the thruster batteries when you're underway?
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Old 12-06-2020, 10:08 PM   #16
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^^^This.

We have 2 group 31 AGM on a standalone charger under the forward berth for the thruster. Short cable runs so max power is drivers to the thruster.

For the house bank, I went with doubled 4/0 cable from the bank to the inverter, and 3/0 to feed the main DC distribution panel.
I like big cables too.

The charging system is a whole 'nuther monster.

I guess I don't understand the advantage of a stand alone charger up front.

What I'm getting at is that when using the thruster I'll either be coming or going from a dock or mooring ball; the only practical charging device that I'll have available in that moment will be the alternator.

What am I missing?
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Old 12-06-2020, 10:13 PM   #17
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Peter, so nothing is charging the thruster batteries when you're underway?
Weíve generally run the genset while underway, so the thruster batteries are being charged. With the revised setup, Iíll be charging the forward bank via the DC-DC charger.
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Old 12-06-2020, 10:20 PM   #18
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Weíve generally run the genset while underway, so the thruster batteries are being charged. With the revised setup, Iíll be charging the forward bank via the DC-DC charger.
That explains it.
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Old 12-06-2020, 10:30 PM   #19
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Weíve generally run the genset while underway, so the thruster batteries are being charged. With the revised setup, Iíll be charging the forward bank via the DC-DC charger.
I donít charge the thruster battery while underway. Only on shore power since we usually donít run the genset underway. Never had any issues that way.
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Old 12-06-2020, 10:47 PM   #20
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I like big cables too.

The charging system is a whole 'nuther monster.

I guess I don't understand the advantage of a stand alone charger up front.

What I'm getting at is that when using the thruster I'll either be coming or going from a dock or mooring ball; the only practical charging device that I'll have available in that moment will be the alternator.

What am I missing?
The standalone charger eliminates a long, heavy DC cable run from the engine room to the thruster. 12v DC is best served by short runs, while 24v or 48v can get away with longer runs without much loss.
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