Dear electrically educated ones...

NewbeeMC9 · July 07, 2010, 08:09:21 PM

Quote from: miles2go on July 07, 2010, 05:59:45 PM
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.

To add info, click on PROFILE

under where it says Modify Profile, click on Forum Profile Information

you can type it in the Personal Text line or the Custom Signature Line

Would love to see a picture of your bus.

One question, Is your Bus system and 50 DN 24V or 12v

I was under the impression that GM's were 12v.

miles2go · July 07, 2010, 10:51:20 PM

Craig,

Ok, got it, 3 batteries in series to make 24v and two strings of 3 in parallel to double amp hours. Somewhere in the range of 300 to 380 AH. Connected with 4/0 cable. The inverter is the Trace 4024. A 250 amp fuse between the positive 24v house bank and the inverter, ok. Use 4/0 cable for the cross tie, ok.

I do not insist, that is the object of asking questions. Controlling the Magnetic switch from the blower relay sounds fine to me as it seems to add the delay that Sean mentions. If the blower motor cut in relay in the GMC 4905 is delayed?. Have to find out, but it sounds great. I still use the 5 amp fuse on the control wire of the magnetic switch though?

The OEM AC and Heat are out of the bus and two Dometic 13,500 BTU roof airs are installed. 250 amp fuse on the cross tie cable next to the coach battery, ok. None on the negative and none on the positive of the alternator, ok. Forget the OEM DC circuit breakers and use fuses, ok. What is a good amperage for the battery shutoff and kind to use? The OEM is old and iffy and needs replacing.

Sean,

If 2/0 cable is for 200 amps (sorry for confusing #2 with 2/0) and a catastrophe fuse for that is 250 amps, by the Cerro wire sizing chart link Craig posted 4/0 is also a 250 amp fuse? Shouldn't the 2/0 be a 200 amp fuse, or is there a "fudge factor" of 50 amps for catastrophe? I don't know, and I am not being smart. I am just being 'fused (I guess now I am being smart

).

NewbeeMC9,

It is 24v. I will try a pic in the profile, if I can find one.

Thank you so much all.
Andrew.

bevans6 · July 08, 2010, 04:09:39 AM

I wondered what the starting surge current is and if a 200 or 250 amp fuse in the cross-tie would negate the ability to use the house batteries for starting aid if that was ever needed?

Brian

miles2go · July 08, 2010, 05:38:37 AM

Brian,

Good question. The 4905 uses 2 12v 8ds connected in series for 24v and the manual says each has 5900 watts average cranking power at 0 degree F. Cold cranking rating of 900 amps, 0 degrees F. 4/O cable is used to connect those to the starter. Under a no-load test the starter has a max amps rating of 95 amps. I pulled that out of the manual so whatever you can infer from that may give a clue?

Andrew.

muddog16 · July 08, 2010, 05:54:50 AM

I borrowed this link over at Bus Nuts......its some excellant food for thought on batteries and some interesting reading! http://www.smartgauge.co.uk/batt_con.html

Some of this is a first reading for me so take it FWIW!

gumpy · July 08, 2010, 06:14:50 AM

Quote from: miles2go on July 07, 2010, 10:51:20 PM
Ok, got it, 3 batteries in series to make 24v and two strings of 3 in parallel to double amp hours. Somewhere in the range of 300 to 380 AH. Connected with 4/0 cable. The inverter is the Trace 4024. A 250 amp fuse between the positive 24v house bank and the inverter, ok. Use 4/0 cable for the cross tie, ok.

Sounds about right. Maybe Sean will check this and provide another opinion. He may be traveling now, though, as they are headed south along the Mississippi.
I use a Trace 4024SW, also, and have 8 6v golf cart batteries. I used 4/0 cable for everything. Battery connections. Battery to inverter. Cross tie.

Quote
I do not insist, that is the object of asking questions.

Didn't mean to imply you were being disrespectful or ignoring advice. Only that you should decided to go that route after evaluating all the available options, including my suggestions for a manual switch rather than automatic.

Quote
Controlling the Magnetic switch from the blower relay sounds fine to me as it seems to add the delay that Sean mentions. If the blower motor cut in relay in the GMC 4905 is delayed?. Have to find out, but it sounds great. I still use the 5 amp fuse on the control wire of the magnetic switch though?

Yes, you should protect the circuit with a fuse. 5 amps is probably overkill. That relay probably requires less than an amp to activate. You may want to consider adding a diode across the coil, too, to prevent reverse emi (that's probably not the correct term) from damaging your alternator when you deactivate the relay.

Quote
The OEM AC and Heat are out of the bus and two Dometic 13,500 BTU roof airs are installed. 250 amp fuse on the cross tie cable next to the coach battery, ok. None on the negative and none on the positive of the alternator, ok. Forget the OEM DC circuit breakers and use fuses, ok. What is a good amperage for the battery shutoff and kind to use? The OEM is old and iffy and needs replacing.

Obtain a take-out shutoff switch to replace the original. Maybe Sam Caylor. Or buy a new one. I got mine from Waytekwire.com. Not cheap, but good quality.

miles2go · July 08, 2010, 06:16:11 AM

Great link Muddog, thanks. My batteries are wired the second way, when the permanent bank goes in I will try the 3rd way.

Andrew.

miles2go · July 08, 2010, 06:19:40 AM

Thanks for the updates craig,

Andrew.

Sean · July 08, 2010, 06:58:19 AM

With 4/0 cable and a Trace SW4024, I would (and do) use a 450-amp catastrophe fuse. 4/0 can carry that much, and the SW4024 under full load can draw about 370 amps. A 250-amp model is too small.

Craig and I disagree on few things, and the source of coil power for the bridge solenoid is one of them. My personal preference is to have such a solenoid bridge when and only when the main alternator is producing ample power. I want the bridge in place when I am driving to get as much inexpensive charge off the big 50DN into my house bank as possible, yet when the sophisticated three-stage charger in the inverter is running, I don't want the dissimilar chassis batteries in the mix to corrupt the charge pattern going in to the much larger and more expensive house batteries.

In addition to this automatic setting driven by the Relay terminal, I also like (and have) a three-position switch that also provides settings to manually override the bridge to either "on" or "off" irrespective of alternator status; the manual "on" position is useful for emergency start (or should you need to charge chassis batteries from the house charger), and the off position is useful for troubleshooting, or getting back that extra ~10 horsepower the alternator is robbing while climbing a hill.

-Sean
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