House / Start Battery Separation Techniques - Best Practice?

[Dsanduril]

Originally Posted by smac999

you always switch the pos, not the neg.

The general rule is that you switch the ungrounded conductor. Hazarding a guess, most marine DC systems have the negative tied to ground, so you switch the positive. That way there is no potential above ground when the switch is off.

But there are DC systems where the positive is grounded, in which case it would be "normal" to switch the negative side. There are also floating DC systems where neither side is grounded, in that case you should generally switch both legs, but it is not uncommon to find a single switch and it can be in either leg.

[Bill Seal]

I just put a high current relay in the Start Batt lead, driven by the Ign switch. When the Ign switch is on, (engine running) it's paralleled with the house batteries. when the switch is off, it floats. I used this system on my Ford diesel van when camping in Baja, never had a problem starting it after sitting on the beach for a week drinking Tecate.
Actually, Volvo doesn't have a contact that maintains continuity when starting, but a diode from the start terminal to the run terminal took care of that.

[deblen]

Originally Posted by Bill Seal

I just put a high current relay in the Start Batt lead, driven by the Ign switch. When the Ign switch is on, (engine running) it's paralleled with the house batteries. when the switch is off, it floats. I used this system on my Ford diesel van when camping in Baja, never had a problem starting it after sitting on the beach for a week drinking Tecate.
Actually, Volvo doesn't have a contact that maintains continuity when starting, but a diode from the start terminal to the run terminal took care of that.

Interesting.-using a HD relay to bridge bat 1 & bat 2 when Ign is ON.

The "Volvo" diode ensures power is maintained on the Ign term. & HD relay stays on during cranking,which bridges bat 1 & bat 2 during cranking?
What happens if house bat is "dead" ? Current rush from start bat to house bat,while trying to crank ?

/ Len

[transmitterdan]

Not too much current will rush from a bank into a "dead" battery when cranking. When cranking the battery voltage is maybe a few tenths above the "dead" battery which is not enough to affect the starting operation. The starter will get almost all the current.

So called"emergency start" systems are on thousands of power boats but work the other way. They use the house bank to parallel a dead starter battery.

But today we have simple automatic relays with manual override available. These would seem like a better way to accomplish the same thing.

[Scrimshaw4]

Some may disagree but I have found that an isolater between the alternator output and battery bank works. Been using them for 30 years on various boats with no problem. Selector switches can be used to alternate and combine the house / starter bank sources.

[deblen]

Originally Posted by transmitterdan

Not too much current will rush from a bank into a "dead" battery when cranking. When cranking the battery voltage is maybe a few tenths above the "dead" battery which is not enough to affect the starting operation. The starter will get almost all the current.

So called"emergency start" systems are on thousands of power boats but work the other way. They use the house bank to parallel a dead starter battery.

But today we have simple automatic relays with manual override available. These would seem like a better way to accomplish the same thing.

I agree there shouldn't normally be a problem paralleling "dead" house & start bat. The house bat is normally discharged,rather than dead.
But-you could have the possibility of a totally flattened or internally shorted,etc house bat,because things get accidentally left on over a period of time.
Current rush could be very high-enough to cause overheating.

That is a very good reason to abandon 123 off swxs, & install a simple VSR,with an "emerg start from house" on/off bridge swx across the VSR. This emerg start swx would allow you to manually bridge the VSR in the event the start bat is "dead" or removed. Note: when properly wired,the VSR senses only the start bat,& will not bridge start & house unless start is above 13.5V Therefore,there is no way to start off the house bat,if the start bat is low,unless you install an emerg start bridge swx across the VSR bat 1 &2 terms.(or use jumper cables,etc)

In addition, an on/off swx for house to panel & on/off for starter to bat. should be used as normal.

Existing 123 off swxs can be re-purposed as on/off swxs,by only using 2 of their terms.

No way should there be any accessible swxs in the alternator output cable to start bat. That's how alt. diodes get fried & electroncs get excess voltage.
/ Len

[deblen]

My boat bat/alt wiring.

https://www.dropbox.com/s/ser8jb2olv..._0001.pdf?dl=0

Critiques?

Cheers/ Len

[Wotname]

Originally Posted by deblen

My boat bat/alt wiring.

https://www.dropbox.com/s/ser8jb2olv..._0001.pdf?dl=0

Critiques?

Cheers/ Len

Maybe it's not shown but I don't see any Voltmeter and I personally prefer an Amp meter that tells me what current is going in or out of the battery rather than what the alternator is doing. Not a criticism, just the way I prefer.

[DeepFrz]

Originally Posted by Scrimshaw4

Some may disagree but I have found that an isolater between the alternator output and battery bank works. Been using them for 30 years on various boats with no problem. Selector switches can be used to alternate and combine the house / starter bank sources.

Yeah they work. Not optimum but they work.

[Wotname]

First up, thanks to all who have posted

Originally Posted by jimbunyard

Seems to me that if the main negative bus was wired to the selector switch/alt/starter ground you'd have something useful. With it wired as drawn, looks like all that's needed at the selector switch position is an on/off switch...

.
Well I think this particular concept was to keep the house negative bus off the engine ground except when using the engine for charging (or starting). Same as with the start negative. When using this circuit, the only time any negative has to be connected to the engine ground is when running the engine.

Originally Posted by smac999

you always switch the pos, not the neg.

While this is the conventional wisdom and a valid opinion, it is not a fact. Note, I also prefer to switch the positive but I can occasionally see benefits doing otherwise.

Originally Posted by RaymondR

I have separated my starting and house systems because I have a steel boat and have experienced electrolysis problems with the underwater hull. I am not sure whether or not the corrosion was related to either of the electrical systems but it appeared to be a wise precaution to try to isolate both of them from the hull.

This turned out to be a little more involved than I thought. The house system was fairly simple as all that was required was to isolate it from the cranking system. The cranking system isolation required a flexible coupling on the propshaft, and mounting the Morse controls on an alloy plate insulated from the steel hull in the cockpit.

…...

I think is the crux of the matter. Metal boats really benefit from keeping the metal isolated from electrics and yet this is not so easy to achieve in practice.

In essence, this circuit goes a long way to achieving this aim without having to totally isolate the engine, running gear, alternator, starter motors etc. The only time the engine is connected to the negative bus is when it is starting/running.

So it might be the poor mans's guide to electrical isolation on a metal boat.

Originally Posted by deblen

The house Main Dist Panel is always supplied with + POS,but the Neg side of various house loads would be connected to Main NEG Buss,which is supplied with swxd Neg.?
So house bank is NOT always on? or am I missing something?

Yep, you are missing something Look again and you will see the Main NEG bus is hard wired to the house battery. It is only the start battery that has it's negative pole connected via the switch. Note though, to charge the house battery from the engine alternator, the selector switch must be switched to house or both.

Not shown were the other charging sources like solar, wind, shore charger etc which were are connected directly to the house Pos & Neg (via the usual regulation, switching and protection devices). So again, these are kept separate from the engine ground.

Originally Posted by roland stockham

My personal view is that 'best pratice' should not include the use of selector switches at all. House and start systems should be kept entirly seperate and each should have its own isolation switch (or or breaker) outside the engine room or other high fire risk area. Even better is to have a separate battery and circuit feeding the essential nav systems to prevent 'dirty' supply from pumps and machinery causing interference. This is particularly important wher a high power inverter is fitted. Charging is then through an external regulator and diode or loss-less splitter. This applies to anything for bluewater or any boat bigger than 26ft.

Yes, this maybe best practice if you include keeping the engine, running gear and hull isolated form either bus. Hard to achieve and unlikely to be seen on many Water boats">blue water boats, especially the sub 50 or 60 ft ones.

Initially I couldn't see much advantage of the described circuit in the opening post but now I'm thinking this is reasonable arrangement for any boat but especially for steel, aluminium and carbon fibre hulls. The main point is that it keeps the hull and engine etc isolated from either pole except when the engine is used.

Of course, it does require the use of manual switching and I know that irks some of us (but not me ). I'm sure the thinking man could overcome this shortcoming with suitable circuitry. Maybe something as simple as solenoid activated by the ignition / start switch to bring the negative pole on line when starting / running and then the usual echo charge or similar.

[deblen]

Originally Posted by Wotname

Maybe it's not shown but I don't see any Voltmeter and I personally prefer an Amp meter that tells me what current is going in or out of the battery rather than what the alternator is doing. Not a criticism, just the way I prefer.

The box @ top of diagram "Eng. Instr. Panel" contains analogue voltmeter for start bat,as well as idiot lights for temp,oil press., charge indicator, & hourmeter. I have a small dig. voltmeter to inst in parallel to analogue voltmeter for finer accuracy.
I also have separate analogue oil press. & temp. gauges mounted near dash.

The inverter has a digital voltmeter(not shown in my diag) that is visible from steering stn. reading house bat. I have a second small dig. voltmeter (like above) for house bat. that I will mount alongside the above start bat dig. meter. These are "roun to it" jobs. (Do they ever end)

Personally,I like an alt. output ammeter,but I agree a house bat. dig. ammeter or fancy amp hr display would be nice. At present,I use inverter voltmeter level as an "indication" of house state of charge. We don't live aboard longer than a few days at a time & as long as the eng. will start,we get by. Solar,wind-possible in future-upgrade as/when reqd.

I can see another improvement to bat swxs arrangement that would allow me to start off either bat without bridging them.

You are correct about the "main Neg buss" being permanently conn'd to start bat.-in the diagram of your OP. I missed that.
Apologies to transmitterdam-he saw it.
Other than possibly isolating the Pos from hull,I can't see any electrical difference in your swxd neg system. The main Neg buss should be wired to the wiper (grd) term of 1,2,all swx,with the existing grd supplied thru an on/off swx. Call it "Main Power" I guess.

Tks for the input
/ Len

[Wotname]

Originally Posted by deblen

The box @ top of diagram "Eng. Instr. Panel" contains analogue voltmeter for start bat,as well as idiot lights for temp,oil press., charge indicator, & hourmeter. I have a small dig. voltmeter to inst in parallel to analogue voltmeter for finer accuracy.
I also have separate analogue oil press. & temp. gauges mounted near dash.

The inverter has a digital voltmeter(not shown in my diag) that is visible from steering stn. reading house bat. I have a second small dig. voltmeter (like above) for house bat. that I will mount alongside the above start bat dig. meter. These are "roun to it" jobs. (Do they ever end).......

. The main Neg buss should be wired to the wiper (grd) term of 1,2,all swx,with the existing grd supplied thru an on/off swx. Call it "Main Power" I guess.

Tks for the input
/ Len

You certainly have your Voltmeters sorted out

I don't understand your point of connecting the main Neg bus to the wiper terminal of the 1,2, all swt. The way it is shown as connected to the 2 makes more sense IMO. This keeps the House battery (2) Neg isloated from the engine ground ex ept when running the engine.

[deblen]

Originally Posted by Wotname

You certainly have your Voltmeters sorted out

I don't understand your point of connecting the main Neg bus to the wiper terminal of the 1,2, all swt. The way it is shown as connected to the 2 makes more sense IMO. This keeps the House battery (2) Neg isloated from the engine ground ex ept when running the engine.

My thot was to not have the main Neg bus conn'd to either Neg bat. when system was off. Reason is to "shut down" the Pos Dist panels source of Neg for it's loads. In other words,as transmitterdam pointed out,with diagram as shown,all the Dist panel loads are operational at all times(assuming all panel breakers are left on).
Aren't we trying to disconnect all power in vessel with,ideally,one main swx?

So- remove the existing "Grd" from Wiper,by inst. an On/Off swx in line with the wiper & Grd. Then disconn Main Neg Bus from Start Bat Neg/Term 2 & conn it to wiper. No grd on wiper unless you turn new On/Off swx on.
No path to either bat neg if wiper is in Off pos. Hence-no DC eqpt can operate. Dead boat.
Turning 1,2,all swx to 2-Dist panel alive.
"" " "" 1- ? can't remember which bat does what-need to print diag,so I have it in front of me
" " " " " " ALL everything works

Make sense?

Still don't see any advantage/difference electrically over normal Pos switching,except possibly easier to isolate bat negs from vessel ,while both swxs are off-boat dead.

Could probably work a HD relay into it to simplify operation,or a VSR(s) in Neg.
Gotta go for now.
Keep thinking on it / Len

[RaymondR]

I have found a large analog panel meter with an expanded scale (10V zener diode in series) to be then handiest thing for keeping an eye on what is going on with the house system. Once you become accustomed to how it behaves under various loads, and when the batteries are charging you pretty well know immediately whether or not there is a problem with the system. The only items I have found to require the occasional monitoring for current are the solar panels and I can see what they are up to on the regulators.

When I built the boat 28 years ago I installed port and starboard 1" conduits and for many years they proved adequate. However when I became a permanent live aboard/cruiser the gadgetry started to proliferate and the conduits have filled up. I have considered a system whereby I would run a number of ring mains, each with a circuit breaker, and use data cable to switch the various loads at the load using mosfets on the negative at the load. I have used this system to switch pumps and it appears to have a number of advantages.

[Badsanta]

For a steel boat you need a floating ground.

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