Dear electrically educated ones...

[miles2go]

Below are threads where advice is given. I would really like to be sure I have it right before I use the advice. Could you please read the thread snippets and comment on my twisted rational? Thanks.

"Sean is figuring you aren't OTR charging, I guess, anyhow the solenoid would be a 200 Amp CONTINUOUS DUTY, with a 24 Volt coil. Big terminals with his cable size recommendations, connect between the positive terminal of the chassis batt, and the positive of the house batts. The small (coil) terminal wires to the switched side of the master, so it is only energized when the master is on. If the solenoid has two small terminals, ground the other one.
I would put a 5 amp fuse in the coil circuit, close to the master switch, cheap fire protection! NAPA, or an RV supply."

"Where I differ from him is in how to connect the coil terminals. I favor connecting the coil either to the relay off the alternator's "R" terminal (so the connection is made only when the alternator is putting out charge) or to the oil pressure switch (so that the connection is made only when the engine is running.

On my system, I even added a delay timer between the alternator signal and the bridge solenoid, to let the engine and alternator come fully up to speed and the chassis batteries to settle before the house system connects. I found that, before adding the delay, the bridge would connect before the starter had even finished cranking.

Since we have a dash switch "over-ride" for our bridge solenoid, we can switch it off when, for example, climbing steep grades, to give that 10hp back to the engine. We just let the air conditioning continue to run from the batteries, then flip the bridge back on when on the downgrade." 

"If you have done away with your OTR air conditioning, you have two 200A 24VDC continuous duty relays in your bus.
They are the contactors utilized for the evap & blower motors in the MCI. I pulled mine from the forward bay ceiling, drivers side (5C).
I used mine to isolate my inverter from the OTR charging system, when parked. This keeps the start batts. for starting only."

"You really should remove the isolator and use a continuous duty contactor to tie the house batteries in parallel when the alternator is 'putting out'. The usual way to drive the contactor is with a relay that has it's 6 volt coil driven off of the 'r' terminal on the alternator. I'm not sure about Eagles but GMs used the 6 volt relay and contactor to power the big fans in the HVAC only when the alternator was working. So much of the wiring could be there already."

"Make sure you put a fuse for the rated current of the alt within 16 inches of the + lug on the alt, and on large house battery packs (~400 CCA amps+) put a catastrophe fuse on the neg side before ground. You could use this "Pathfinder" thing if it is a tie-in switch, but it's cheaper to go with a marine-type battery switch that does the same thing (but not automatic, which may be what you're after)."

End of snippets.

So, I have six 8v golf cart batteries in two strings of 3 each, and two 8D's. The two strings (of 3x8v=24v) are connected to the inverter positive and negative DC inputs (I need dc fuses here, but not sure of the amperage). This is between 300 and 380 AH, I can't be exact as I bought them used to use as test batteries, with no indication of amp hours or model number, and they will be replaced with 800 AH bank soon, I hope.

Is this below what needs to be done?

Connect a #2 cable from the positive terminal of the second 12v battery in the 24v string of two 8D's. To this connect the OEM condenser fan relay 672758 (GM Delco? magnetic switch), which some say is 200 amp continuous but it is fed from a 150 amp OEM breaker? (In the wiring diagram it is fed from a 90 amp breaker with a #2 cable and in the manual a 150 amp breaker with a #2 cable... who knows?) To the other terminal of the condenser fan magnetic switch connect the positive terminal of the last 8v battery in the second string of 3 with #2 cable.

One of the two smaller terminals connects to the Generator Relay. Of the 4 terminals on the generator relay #1 is power from the battery junction bus, #2 is connected through a 10 amp fuse to the AC/HEAT relay, #3 is Generator "R" terminal connection, and #4 is the ground connection. So I ask is it terminal #2 I connect the small terminal of the magnetic switch to through a 5 amp fuse? (Power from the battery junction bus can not flow through to the AC/Heat relay until the generator "R" terminal closes the relay.)  Then the remaining small terminal on the magnetic switch is grounded, where should I ground it?

Does the delay timer (can anyone provide a model number or description of this so I can get one) go in the line from the Generator "R" terminal #2 of the Generator relay to the small terminal of the magnetic switch, so it delays the signal until the engine is running? Before or after the 5 amp fuse?

The dash switch over-ride, is it just breaking the connection from the generator "R" terminal relay to the magnetic switch with a simple switch ? Does this connect before or after the fuse and delay timer relay?

If the "rated current" of the 50DN is 270 amps do I need a 300 amp DC fuse within 16" of the plus lug on the 50DN?

What size "catastrophe fuse" on the negative side before ground? Is this on the 2 8D cranking batteries?

As the house battery bank is temporary and will be replaced with a larger set, hopefully 800 AH or so, do I need large DC fuses between the house batteries and the inverter.

There are three circuit breakers in the battery compartment on the battery bus bar. 50 amp for the drivers electrical panel, 60 amp for the blower motors and water pump and 150 amp for the condenser fan and magnetic switch. The OEM A/C has been removed so the 60 and 150 are not used. Can these be utilized where I need DC breakers of 60 or 150 amps?

Thanks,
Andrew.

[gumpy]

So, I have six 8v golf cart batteries in two strings of 3 each, and two 8D's. The two strings (of 3x8v=24v) are connected to the inverter positive and negative DC inputs (I need dc fuses here, but not sure of the amperage). This is between 300 and 380 AH, I can't be exact as I bought them used to use as test batteries, with no indication of amp hours or model number, and they will be replaced with 800 AH bank soon, I hope.

Wait... golf cart batteries are 6 volts. Do you mean eight 6V batteries?  I'm guessing not, since you went on to sho 3x8V.  Please clarify this. What batteries are you using?  How many cells in each?


I can't even continue with the rest of your post until this is clarified. I'm unaware of any 8v batteries.

[luvrbus]

Watch out Gumpy Sam's even sell the 8V golf cart batteries 

good luck

[miles2go]

They are indeed 8v. i thought they were 6v when i got them but they tested 8v so i strung them times 3 to equal 24v.
Andrew.

[gumpy]

Watch out Gumpy Sam's even sell the 8V golf cart batteries 

good luck

Really?  Wow, that's a new one on me!  Of course it's been about 7 years since I put mine in, so I haven't looked at batteries for a long time.

I stand corrected.

[BobBoyce]

Four cell 8V golf cart batteries are becoming more popular these days due to less of them required for the more commonly newer 48V and rarer higher voltage golf carts.

Bob

[luvrbus]

The 8 volt are not new they been around a long as I can remember I know they were here in the 50's we used those on the hard starting flat head Fords that were 6 volt hell on headlights but they would start the Fords lol I am sure there are more old farts here remember that



good luck

[NewbeeMC9]

Miles2go,

Welcome to the madness!


Go ahead and fill in your bus specifics and info.  would help with your questions.



I'll answer one of your questions,   Yes




You need a Fuse between Inverter and batteries.   I have a 4Way marine switch and have the fuse between it and the inverter.  (and no jjr it is still in it's temporary mounted position )

[miles2go]

Bob said "newer 48v golf carts", not implying the 8v batteries were newer. I only bought them because I thought they were 6v Trojans but they turned out to be 8v. they are still good for my trial and practice though. I used 4/0 cable so I will use a 250 amp breaker on the DC positive cable to the inverter. i s that correct?
Thanks,
Andrew.

[Sean]

Andrew,

First off, it's very hard to follow the "snippets" since they are taken out of context and do not necessarily relate one to the next.  I recognize some of my own writing in there and I know there was more to what I wrote.

Secondly, for 200 amps you need 2/0, not #2 as you wrote.

Third, I am concerned about the odd mix of batteries.  Either use the 8v golf carts, or the 8D's, but not both.

Fuse (and cable) sizing depends on load and charge sources, and you'll need to give us more information.  But generally a catastrophe fuse on a 2/0 system would be 250 amps and you can find those in ANL.

Delay timers are available from Newark, Allied, and many others and come in every conceivable size, duration, and rating.  The timer contacts go between the R output and the bridge solenoid coil.

Perhaps you can sketch out what you are thinking here; that would make it easier to assist you.

-Sean
http://OurOdyssey.BlogSpot.com

[miles2go]

Not sure how to , or where to do that. She is a 1973 GMC 4905. Is a fuse better than a circuit breaker then?
Andrew.

[miles2go]

On the not sure how to, or where to do that... that was to the profile request not the "sketch out what I am trying to do" So I will try to sketch it out. I have 8D start batteries. I don't think I should use Golf carts for that or 8D starts for the house, sorry I was confusing but I thought the 50 DN would charge both types while underway?
Andrew

[Sean]

... I have 8D start batteries. i don't think i should use Golf carts for that or 8D starts for the house, sorry i was confusing but I thought the 50 DN would charge both types while underway?

Sorry, I meant not to mix the types in a single bank.  Different types for house and start are common, and, yes, with a bridge solenoid or isolator you can change both while under way.

Breakers are fine, but expensive in the larger ratings.

-Sean
http://OurOdyssey.BlogSpot.com

[gumpy]

So, I have six 8v golf cart batteries in two strings of 3 each, and two 8D's. The two strings (of 3x8v=24v) are connected to the inverter positive and negative DC inputs (I need dc fuses here, but not sure of the amperage). This is between 300 and 380 AH, I can't be exact as I bought them used to use as test batteries, with no indication of amp hours or model number, and they will be replaced with 800 AH bank soon, I hope.

Ok, so we've established you have 8v batteries. Connect them in series, and then in parallel to the inverter. If they are golf cart batteries, they are probably around 250 ah each, so multiply that by 2 (because you have 2 strings in parallel). That tells you what your capacity is in 24v.

How big is your inverter? Need that to determine draw and required wire size.

Yes, you need a DC fuse between your batteries and your inverter. Again, depends on wire size, which depends on the draw of the inverter.

Is this below what needs to be done?

Connect a #2 cable from the positive terminal of the second 12v battery in the 24v string of two 8D's. To this connect the OEM condenser fan relay 672758 (GM Delco? magnetic switch), which some say is 200 amp continuous but it is fed from a 150 amp OEM breaker? (In the wiring diagram it is fed from a 90 amp breaker with a #2 cable and in the manual a 150 amp breaker with a #2 cable... who knows?) To the other terminal of the condenser fan magnetic switch connect the positive terminal of the last 8v battery in the second string of 3 with #2 cable.

This is confusing.  I don't understand second in the string, last 8v, etc.  
Here, let me clarify for you.
You have 2 8Ds for starter batteries, correct?  They are each 12v.  They are connected in series to make 24v. So one side is 24v, one side is ground, and the center is 12v.

So if you are trying to cross tie your house batteries to your coach batteries so you can charge off the engine alternator, then yes, connect the 24v side of the coach battery to one side of the relay and connect the 24v side of the house battery to the other side.  

#2 wire is good for 95 amps at 140*F (http://www.cerrowire.com/default.aspx?id=46).  That's not enough. Your alternator is rated at 270 amps. In reality, you may see a bit over 100 amps going across your cross tie line, but it could be higher. I recommend you use 4/0 welding cable.

One of the two smaller terminals connects to the Generator Relay. Of the 4 terminals on the generator relay #1 is power from the battery junction bus, #2 is connected through a 10 amp fuse to the AC/HEAT relay, #3 is Generator "R" terminal connection, and #4 is the ground connection. So I ask is it terminal #2 I connect the small terminal of the magnetic switch to through a 5 amp fuse? (Power from the battery junction bus can not flow through to the AC/Heat relay until the generator "R" terminal closes the relay.)  Then the remaining small terminal on the magnetic switch is grounded, where should I ground it?

Personally, I don't like connecting your relay to the alternator. It prevents you from charging your bus batteries off the inverter charger when plugged into shore cord.  I prefer a manual switch.

However, if you insist...  is the relay 12v or 24v. it matters because on the MCI (don't know what bus you have), the blower relay is 12v and is driven off the alternator R terminal. If you relay has a
24v coil (most likely), this may not work. I say may, because it might actually energize on 12v.
An alternative might be to connect into the blower relay output. That way, when the alternator and air pressure are up, and the blower cut-in relay is activated, then the crossover relay will also
be activated.

Also, I caution you again on using the automatic method if you still have your coach heat and A/C installed. You might find that the A/C and crossover together require more juice than your little 50DN
can put out.

Does the delay timer (can anyone provide a model number or description of this so I can get one) go in the line from the Generator "R" terminal #2 of the Generator relay to the small terminal of the magnetic switch, so it delays the signal until the engine is running? Before or after the 5 amp fuse?

See comment above re: blower cut-in relay.

The dash switch over-ride, is it just breaking the connection from the generator "R" terminal relay to the magnetic switch with a simple switch ? Does this connect before or after the fuse and delay timer relay?

If the "rated current" of the 50DN is 270 amps do I need a 300 amp DC fuse within 16" of the plus lug on the 50DN?

What size "catastrophe fuse" on the negative side before ground? Is this on the 2 8D cranking batteries?

I put a 250 amp fuse on my cross-tie cable up next to the coach battery. There is not a fuse coming off the alternator to the coach battery, that I'm aware of.
I see no reason to  have one in the negative side.  Having said that, I just fried a 12ga ground wire and nearly caught my bus on fire. I corrected the mistake that caused
this, and still don't have a fuse in the negative side.

As the house battery bank is temporary and will be replaced with a larger set, hopefully 800 AH or so, do I need large DC fuses between the house batteries and the inverter.

See comments above regarding size of inverter and wire size.

There are three circuit breakers in the battery compartment on the battery bus bar. 50 amp for the drivers electrical panel, 60 amp for the blower motors and water pump and 150 amp for the condenser fan and magnetic switch. The OEM A/C has been removed so the 60 and 150 are not used. Can these be utilized where I need DC breakers of 60 or 150 amps?

Yes, but you might find those odd numbers in your setup.  Your cross-tie will be higher than either of those. Maybe your inverter will be that low, but unlikely with that size of battery bank. Still, you might find a use for them. Don't skimp on cost if it means skimping on safety.

craig

[miles2go]

Sean,
I am trying to charge my 8d start batteries as well as my house battery bank while underway with the 50DN. Almost all of the snippets were dealing with that topic, I think.  Sorry if I gave the impression that something was misleading by being out of context. Maybe it is because the very first sentence should have been omitted also.

Anyway, I would like to use the "magnetic relay " to effect an "isolator" between my start bank and my house bank.

Andrew.