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Author Topic: What is best way to hook alternator to house batteries?  (Read 2454 times)
belfert
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« on: September 05, 2009, 10:54:00 AM »

I figured out that my A/C selenoid still works even with the entire A/C system electrical panel removed.  There is a desh switch that used to power on the heating/air conditioning system.

What is the recommended way to actually tie into my house batteries?  I have a large circuit breaker.  Should I connect on the battery or the load side of the breaker?  What about grounding?  I assume I need to tie into the chassis for a ground.
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« Reply #1 on: September 05, 2009, 11:06:48 AM »

I dunno from "best" but our house batteries are fused in the positive line right at the batteries.  From there the cable runs directly to the house disconnect.  The disco is connected to a common post which supplies all the house loads (12 V panel & inverter).  There is a crossover cable - looks to be about 2/0 - from that common post to a continuous duty solenoid located in the coach battery compartment.  Its one of those little silver jobs that looks like a Ford starter solenoid from the 60's.  That solenoid is energized whenever the key is on.  I have recently added a toggle switch in the key circuit so that I can control when the crossover is engaged.
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« Reply #2 on: September 05, 2009, 11:20:25 AM »

Fellows,

Is there a fairly recent wiring diagram for converting a bus? I would think that someone would have published a really good "How To Electrical Systems" for bus conversions?

I am just starting my conversion and two areas that I feel would be great to have a proven design would be the plumbing/water systems and the electrical system.

Doug
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« Reply #3 on: September 05, 2009, 11:29:18 AM »

Sean is the man for you here. Maybe he will chime in. He told us how to do it, but I don't have access to that email right now.

God bless,

John
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« Reply #4 on: September 05, 2009, 12:16:11 PM »

I dunno from "best" but our house batteries are fused in the positive line right at the batteries.  From there the cable runs directly to the house disconnect.  The disco is connected to a common post which supplies all the house loads (12 V panel & inverter).  There is a crossover cable - looks to be about 2/0 - from that common post to a continuous duty solenoid located in the coach battery compartment.  Its one of those little silver jobs that looks like a Ford starter solenoid from the 60's.  That solenoid is energized whenever the key is on.  I have recently added a toggle switch in the key circuit so that I can control when the crossover is engaged.

I got a heavy duty DC breaker from a UPS for free that I use near my house batteries.  It acts as overload protction and disconnect.  It sounds like I should connect to the house side of the breaker.  The selenoid itself should be able to act as a disconnect for the connection from the alternator to the house system.

I forgot about Sean's excellent diagrams.  For some reason Smugmug won't load for me so I can't see his work right now.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #5 on: September 05, 2009, 12:41:13 PM »

I got Sean's excellent electrical diagram to load now and he connected the alternator to the battery side of is fuse and disconnect.

My inverter/charger is on the house side of my breaker so I would think it makes sense to connect the alternator to the house side of things.  The only issue would be if the breaker trips the inverter/charger and alternator would still be supplying power to the bus, but not to the battery bank.
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« Reply #6 on: September 05, 2009, 01:09:19 PM »

I dunno from "best" but our house batteries are fused in the positive line right at the batteries.  From there the cable runs directly to the house disconnect.  The disco is connected to a common post which supplies all the house loads (12 V panel & inverter).  There is a crossover cable - looks to be about 2/0 - from that common post to a continuous duty solenoid located in the coach battery compartment.  Its one of those little silver jobs that looks like a Ford starter solenoid from the 60's.  That solenoid is energized whenever the key is on.  I have recently added a toggle switch in the key circuit so that I can control when the crossover is engaged.


I like having separate control from the run switch. In the event the house batteries are very low and maybe the bus batteries not at their best, you don't want the connection made until the alternator is charging.  Using the "R" terminal on the alternator or a fuel pressure switch is another way to control that.
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« Reply #7 on: September 05, 2009, 04:37:30 PM »

What is the recommended way to actually tie into my house batteries?


There are several ways to do this; "recommended" is very subjective.  That said, I do indeed have one, which is to use a heavy-duty, 200-amp (or bigger) contactor or solenoid rated for continuous duty.  Operate the contactor coil with DC from the chassis side, gated through either an oil pressure-operated relay, or better still a relay operated off the alternator's "R" or "Relay" terminal.  Install a manual momentary switch to bypass this gate, for emergency starting purposes.

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I have a large circuit breaker.  Should I connect on the battery or the load side of the breaker? 


The alternator cross-tie should connect to the battery side of your fuse,  Optionally, you can add something like a class-T fuse rated for 300 amps or so on the tie line.  You don't want to bypass the breaker by connecting to the load side; a short in the load would have no way to trip anything when the alternator is running.

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What about grounding?  I assume I need to tie into the chassis for a ground.


No, run separate ground wires the same size as the positives.  You don't want 200+ amps flowing through the chassis.  Leave the existing chassis ground in place.

Is there a fairly recent wiring diagram for converting a bus? I would think that someone would have published a really good "How To Electrical Systems" for bus conversions?


I recommend "Designing Electrical Layouts for Coach Conversions" by George Myers:
http://www.busnut.com/epicconversionsupport.html

Also, learn your way around the advanced search function here on the board (between "Help" and "Profile" on the navigation bar, above) -- pretty much everything you want to know has been discussed here at one time or another.

I got Sean's excellent electrical diagram to load now and he connected the alternator to the battery side of is fuse and disconnect.

My inverter/charger is on the house side of my breaker so I would think it makes sense to connect the alternator to the house side of things.  The only issue would be if the breaker trips the inverter/charger and alternator would still be supplying power to the bus, but not to the battery bank.


Again, see my comments above.  Add additional protection if you want to between the two battery banks.

I dunno from "best" but our house batteries are fused in the positive line right at the batteries.  From there the cable runs directly to the house disconnect.  The disco is connected to a common post which supplies all the house loads (12 V panel & inverter).  There is a crossover cable - looks to be about 2/0 - from that common post to a continuous duty solenoid located in the coach battery compartment.  Its one of those little silver jobs that looks like a Ford starter solenoid from the 60's.  That solenoid is energized whenever the key is on.  I have recently added a toggle switch in the key circuit so that I can control when the crossover is engaged.



I like having separate control from the run switch. In the event the house batteries are very low and maybe the bus batteries not at their best, you don't want the connection made until the alternator is charging.  Using the "R" terminal on the alternator or a fuel pressure switch is another way to control that.


To amplify on this point, having the solenoid energized whenever the key is on means that, effectively, you are starting the bus from the house bank -- the chassis bank only provides the power to energize the solenoid.

I favor the relay terminal, and even then, the solenoid connects before the cranking is finished.  This has the effect of having the house batts provide some of the cranking juice, but also has the contacts closing under load, leading to possible arc pitting.  I ended up putting a delay timer in between the R terminal and the solenoid, so it connects 30 seconds or so after the alternator starts charging.  This also keeps that extra 10hp of load off the engine while it is stone cold.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #8 on: September 05, 2009, 06:08:35 PM »

The alternator cross-tie should connect to the battery side of your fuse,  Optionally, you can add something like a class-T fuse rated for 300 amps or so on the tie line.  You don't want to bypass the breaker by connecting to the load side; a short in the load would have no way to trip anything when the alternator is running.

Thanks for correcting me on where to connect the line from the alternator.  I got confused even though I looked at your wiring diagram.

Should I hook up to the negative post on the chassis battery bank for my ground?  My understanding is that the DN50 is grounded through the engine.  I had to remove the DN50 a while back and there is only one large cable to it.  I have to see if I have enough 4/0 cable left for this or if I need to order more.  I do have to order lugs as I can't find anyone locally with the right size ones.

I already have a 200 amp selenoid that used to control the A/C and heating system.  There is a dash switch that turns the selenoid on and off.  I assume the selenoid won't activate if the alternator isn't working.
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« Reply #9 on: September 05, 2009, 08:01:17 PM »

I have a 12v system on my bus.  And virtually everything, the starter, 300amp alternator, etc is grounded through the chassis.  My bus is steel framed with aluminum skin and after 32 years, still no electrolysis.

Since I have a 300amp alternator, I bought two 150amp continuous duty solenoids (they look like Ford starting solenoids) and strapped them together with 1/4 inch steel plate to carry the current.  The two solenoids are between the deep cycle and starting batteries.  I have an on-off-on switch on the dash so I can either activate it with the ignition, or the other way with the deep cycle batteries (in case the starting batteries are dead).  I have started the bus through this solenoid when the starting batteries have been dead.  No maintenance issues in 15 years it's been on the bus.  Good Luck, TomC
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« Reply #10 on: September 05, 2009, 09:47:38 PM »

Should I hook up to the negative post on the chassis battery bank for my ground?  My understanding is that the DN50 is grounded through the engine.  I had to remove the DN50 a while back and there is only one large cable to it.  I have to see if I have enough 4/0 cable left for this or if I need to order more.


Yes, the alternator is grounded through the engine.  In an efficient setup, the chassis batteries will be close by, and there would be a ground strap from the engine or cradle to the negative battery post.  Note that there will also be a battery "sense" lead from the regulator direct to the battery positive post.

In a perfect world, the house batteries and their major loads such as an inverter would be close to the chassis bank, but that's often hard to do.  My start batteries are in the back, but my house bank is up front, some 25' or so away.

It's the connection between the two where I suggest you have a direct connection for both positive and negative.  That said, you will end up with frame ties at both ends, too, and inevitably a fair amount of return current will go through the chassis.  But the direct connection makes the whole setup more efficient.

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I already have a 200 amp selenoid that used to control the A/C and heating system.  There is a dash switch that turns the selenoid on and off.  I assume the selenoid won't activate if the alternator isn't working.


If it is still wired as the stock "blower" solenoid, then, yes, it is driven from the alternator Relay terminal.  That should work just fine.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #11 on: September 05, 2009, 10:45:17 PM »

To amplify on this point, having the solenoid energized whenever the key is on means that, effectively, you are starting the bus from the house bank -- the chassis bank only provides the power to energize the solenoid.

I hope you mispoke here.  What it actually means is that the house bank is assisting to start but the house bank is only peripherally involved in our case.  There is a lot of resistance between the house batteries in the spare tire compartment and the starter c/w the path from the start solenoid to the coach batteries.  I'm sure there's some amps flowing through that crossover cable when we start but to say that all the chassis batteries do is energize the solenoid is silly.
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« Reply #12 on: September 05, 2009, 11:10:00 PM »

Yes, the alternator is grounded through the engine.  In an efficient setup, the chassis batteries will be close by, and there would be a ground strap from the engine or cradle to the negative battery post.  Note that there will also be a battery "sense" lead from the regulator direct to the battery positive post.

There is a large ground strap from the engine to the chassis.  (There is no cradle like a lot of buses.)  I have no idea where the large cable from the negative on the battery bank goes to.  It must ground to the chasss somewhere.

My chassis batteries and house batteries are maybe 5 or 6 feet apart.
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« Reply #13 on: September 06, 2009, 12:11:09 AM »

I hope you mispoke here.  What it actually means is that the house bank is assisting to start but the house bank is only peripherally involved in our case.  There is a lot of resistance between the house batteries in the spare tire compartment and the starter c/w the path from the start solenoid to the coach batteries.  I'm sure there's some amps flowing through that crossover cable when we start but to say that all the chassis batteries do is energize the solenoid is silly.


I don't know for sure in your case, but I would ask if you've measured it?  A lot depends on the relative size of the banks.

In our case, we have two group-65 starting batteries (more than adequate to spin the big Detroit) back by the engine, and a massive 8x8D AGM house bank, over the front wheel wells.  I would guess that's only a bit closer together than yours.  The banks are connected with 00 (two-ought).  By contrast, the alternator, chassis batteries, and starter are wired with 0000 (four-ought).

I happen to have a bi-directional ammeter wired into the cross-over, so I can monitor how much power is coming across the tie.  It reads to 200 amps in the forward (from chassis to house) direction, and to 100 amps in the other (long story -- I got the meter on surplus).

Before I put the time delay in, when the solenoid engaged mid-crank, the meter would peg (I'd say the peg was around the 110-amp mark) every time, and it pegged hard -- I'm going to say that a good 150 amps or more was flowing from the house batteries to the starter during cranking.  And mind you, that's after the engine was already spinning fast enough for the alternator to energize its Relay terminal.

I wanted to put the starting load back where it belonged, on the starting batteries, as well as being kind to my poor ammeter's needle, so I added the time delay.

So I think you might be surprised if you actually measured how much current comes out of your house bank during cranking.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #14 on: September 06, 2009, 08:11:54 AM »

We have two runs of 4/0 from the chassis bank to the starter solenoid and 2 x 8Ds for start batteries.  The other distances are likely similar and we have a 2/0 crossover as well.  You've got my curiosity aroused and I should be able to tell what is coming out of the house bank with my Trimetric.  It will be a few days before I can measure it though because right now its just me and the cat.  He's got really good eyes but I just can't teach him his numbers.
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