Reply
 
Thread Tools Display Modes
 
Old 05-01-2008, 01:01 AM   #11
Bus Nut
 
oldog12's Avatar
 
Join Date: Aug 2006
Location: Illinois
Posts: 381
Re: How do you choose the battery isolator size?

You guys got me thinking..... and confused....

Now... I was under the impression that a battery isolator would isolate the banks of batteries, (coach and house), but now, I'm a little confused.... Does the isolator isolate each battery separately instead of each bank of batteries?

So therefore I need a battery switch between the coach and house batteries and then isolate each battery in each bank... is that right? Or do I have it all sideways???
oldog12 is offline   Reply With Quote
Old 05-01-2008, 06:49 AM   #12
Skoolie
 
Train-train's Avatar
 
Join Date: May 2007
Location: Michigan
Posts: 100
Re: How do you choose the battery isolator size?

I would think that each battery or group of batteries that power the house would be considered one unit to isolate from another unit such as the starting battery or batteries. ( One isolator to separate the starting power from the cabin power).

On the other subject of Disconnects, how much currant does a starter for a 5.9 Cummins draw? The size of my battery leads are bigger than a quarter( coin size) in diameter. the lead connection screws down on a post, but that size is much bigger than any of the disconnects I have came across. And those disconnects are rated up to 190 amps continuous, 1000 amp intermittent. I can not imagine how one could connect the battery leads to one of these disconnects.
Train-train is offline   Reply With Quote
Old 05-04-2008, 03:22 PM   #13
Bus Crazy
 
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,096
Re: How do you choose the battery isolator size?

Quote:
Re: How do you choose the battery isolator size?
Sent at: Wed Apr 30, 2008 11:37 pm
by odyssess

what does this mean "Includes an additional terminal for exciting the alternator in start/run." I found a 200 amp isolater that has this extra terminal. Do you know what this means and is used for? Thanks Redbear.
Sorry I didn't see this PM sooner - I just peeked at the board a couple of times in the last few days - after 10 hour days at work. I look at my email in this house account only 2-3 times per week. Others may have the same question.

I looked at the GM version of the isolator in the eBay link posted by oldog 12, which has the fourth "Ignition" terminal you describe added to "excite" the alternator. It is listed as needed for "one-wire" alternators with an internal voltage regulator.

An alternator makes power by spinning one of two sets of windings. One set is the output, the other set of "field" windings act as an electro-magnet. The field windings are powered by the voltage regulator. (Some wind turbines being used by the alternate power bunch use permanent magnets, but the output voltage varies widely with speed. That's another story.)

The alternator makes 3-phase AC, which is fed through a set of internal diodes that put out pulsed DC. The vehicle battery smooths out the pulses as far as the devices being powered are concerned, like a pressure tank on a well pump.

To control the alternator output voltage, so it doesn't burn up all the 12-volt (or 24-volt) devices when the RPM's go up, there is a voltage regulator. This has a 'sense' input that measures the voltage at the battery feed. This wire usually (but not always) also serves as the regulator power input, too. Based on the sense voltage, the regulator has a "dimmer" circuit that feeds a controlled amount of battery voltage out to the field coil, which weakens or strenghtens the magnetic field interacting with the output coil and so adjusts the resulting voltage.

Some regulators are external to the alternator. Alternators for these regulators have at least 2 wires, the field and the output (plus grounding through the case). A standard three-terminal isolator is fine for these. Power for the field windings comes through the external regulator.

Some alternators have internal regulators, and these "one-wire" alternators use the single battery terminal as the regulator input and charging output. They adjust the output to what the battery SHOULD take, and don't allow for losses in the wiring. If you looked at the link posted by oldog 12, the vendor had a different version of isolator for certain years of GM models, which used 'one-wire' alternators, and have the extra terminal.

WIth the diodes in an isolator creating "one-way" valves from the alternator to the batteries, a one-wire alternator cannot draw voltage to the internal regulator to turn on the electro-magnet and get the alternator started. By having an 'ignition" or "start/run' terminal, the alternator can get voltage from the battery when the key is on, create a magnetic field, and get the alternator started. This is likely a diode working in the opposite direction from the charging ones.

The one-wire alternator is simpler, and is easier for mechanics (many of whom don't understand wiring, in my experience) to work with. The alternator system with an external regulator is more complicated, but can give more precise control as components deteriorate. Neither will adjust for a corroded battery cable, because it's unusual for the separate sense wires going right to the battery terminals.

The four-terminal isolator could be used for either type of alternator, just leave the ignition post disconnected if it's not needed. With a one-wire alternator, BE SURE that the ignition input turns on and off with the engine. If you connect the terminal direct to the starting battery, and if the house battery discharges down to 1.4 volts below it (0.7 for the house battery diode plus 0.7 for the ignition diode), the starting battery will start to flow current to the house through the ignition terminal, and defeat the isolator purpose.
__________________
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
Redbear is offline   Reply With Quote
Old 05-04-2008, 03:49 PM   #14
Bus Crazy
 
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,096
Re: How do you choose the battery isolator size?

Quote:
Re: How do you choose the battery isolator size?
by oldog12 on Thu May 01, 2008 12:01 am

You guys got me thinking..... and confused....

Now... I was under the impression that a battery isolator would isolate the banks of batteries, (coach and house), but now, I'm a little confused.... Does the isolator isolate each battery separately instead of each bank of batteries?

So therefore I need a battery switch between the coach and house batteries and then isolate each battery in each bank... is that right? Or do I have it all sideways???
Your original impression, and Train-Train's response are correct - the isolator separates the two battery systems. A "battery" is a group of cells (or cannons) working together as one, whether they are in the same case or not. Your car battery is 6 cells in one case, a big skoolie "house" battery might be 18 cells housed in three pairs of golf cart batteries.
(Those alkaline thingies marked D, C, or AA are really 'cells' and individually are not true 'batteries.')

If you use an isolator system, you will need one battery switch if you want to shut off the house battery system, and another one if you want to shut off the starting battery system.

The simplest DC system, which mirrors how tow vehicles charge trailers, is this:
Instead of using an isolator, simply have a switch or solenoid that joins the two systems together for charging (and possible boost starting) when the engine is running, and separates them when it's not. This is usually sufficient, but can lead to the good battery (bank) and alternator being drawn down, and the resultant vehicle low-voltage problems, if the other one is really dead when you start out.
__________________
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
Redbear is offline   Reply With Quote
Old 05-05-2008, 03:37 PM   #15
Bus Nut
 
Les Lampman's Avatar
 
Join Date: Nov 2003
Location: Whidbey Island, Washington (USA)
Posts: 465
Re: How do you choose the battery isolator size?

A much better technology than the old isolators used in the past is the VSR or Voltage Sensing Relay; also known as an ACR or Automatic Charging Relay. These units sense the voltage of the battery (or batteries in the case of dual sensing units) and combine them when a set of conditions is met. Often when the "starting " battery is over 13.7 volts as an example. They break the connection when the voltage is low to protect the other battery (or batteries) in the system. They do not have the voltage drop across them that the isolators do and can be mounted anywhere.

Here's a link to just one of many...

http://bluesea.com/category/2/productline/overview/389

There's lots of good info in the tech papers on this site; they're one the of the premiere suppliers to the boat industry and there goods are often used in high end RVs.
__________________
Les Lampman
1982 Thomas Saf-T-Liner Pusher "Illusion"

Skoolie.net Gallery
Illusion's SmugMug site
Les Lampman is offline   Reply With Quote
Old 05-06-2008, 12:28 PM   #16
Bus Nut
 
swinada's Avatar
 
Join Date: Mar 2007
Location: Northern BC Canada
Posts: 538
Re: How do you choose the battery isolator size?

Quote:
Originally Posted by Les Lampman
A much better technology than the old isolators used in the past is the VSR or Voltage Sensing Relay; also known as an ACR or Automatic Charging Relay. These units sense the voltage of the battery (or batteries in the case of dual sensing units) and combine them when a set of conditions is met. Often when the "starting " battery is over 13.7 volts as an example. They break the connection when the voltage is low to protect the other battery (or batteries) in the system. They do not have the voltage drop across them that the isolators do and can be mounted anywhere.

Here's a link to just one of many...

http://bluesea.com/category/2/productline/overview/389

There's lots of good info in the tech papers on this site; they're one the of the premiere suppliers to the boat industry and there goods are often used in high end RVs.
Yeh sure now you tell me, after i just ordered one of those Isolators.
__________________
Proud owner of a: 1996 Thomas Safe-T-Liner,Cummins 6CTA 8.3Lt diesel, Allison AT.
http://picasaweb.google.com/swinada/BusPictures http://www.swinada.com/bus.htm
http://lh4.ggpht.com/swinada/SL91F-b...opbussmall.jpg
swinada is offline   Reply With Quote
Old 05-18-2008, 03:19 PM   #17
Bus Crazy
 
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,096
Re: How do you choose the battery isolator size?

Quote:
Les Lampman wrote:
A much better technology than the old isolators used in the past is the VSR or Voltage Sensing Relay; also known as an ACR or Automatic Charging Relay
I've been chewing on this one for a couple of weeks. I guess the hot button for me was the term "better technology" as opposed to "more advanced technology," which I would certainly agree with. "Better" is a subjective term, and what is better for any purpose depends on the use. I think we agree a chainsaw cuts 'better' than a steak knife, but I wouldn't cut a steak with a chainsaw, nor a tree branch with a steak knife (MacGyver excepted). Like most things, there is usually not a "one size fits all" solution.

I hadn't been exposed to ACRs. They are a nifty technology. I'm sure an ACR would be great for a full-timing relative of mine, intelligent but not an electrical whiz, who goes from genset to power pole due to necessary medical equipment onboard. The ACR can be installed in bi-directional mode, so if either the starting battery and alternator or the house battery and shoreline charger reaches 13.7 volts, the battery banks are joined to share the charge, until such time they both discharge to 12.6 volts and disconnect.

A word of caution for anyone joining battery banks with an isolator, relay or switch - be sure the cell types are the same. Connecting expensive gel-cell or AGM house batteries to an alternator or smart charger calibrated for wet cells (starting, golf cart, or deep cycle) might result in cooking out the capacity of the cells. If you are going to use sophisticated cells, be sure to do your homework on the battery manufacturer's requirements for charging.

What I don't like about ACRs is that when you shut off the bus, the ACR doesn't disconnect until the required discharge has taken place. They also draw a watt and a half to hold the coil in while joined.

If the opposite battery is very low, and it bogs down the charging source, the ACR will disconnect, and after the battery being charged is back up for 30 seconds, it will try again. It will continue to pulse on and off until the low battery bank gets at least a surface charge. I don't like all the make/break events. An isolator will let all loads run off of their own battery banks while it devotes full output to the low battery bank.

Quote:
They do not have the voltage drop across them that the isolators do and can be mounted anywhere.
I love the fact the ACRs are sealed (to prevent explosions on gasolene yachts, no doubt) and don't require a protected location. Howver, the voltage drop on an isolator is only an issue in that 1) the heat must be dissipated, and 2) with a "one-wire" alternator, the lost charging voltage is not compensated for. An alternator with an external regulator which senses the chassis system voltage will be "turned up" to compensate for the lost voltage. You have voltage drop across the diodes inside the alternator, anyway.

Another disadvantage of isolators is that if you want to top off both battery systems from a charger on a shoreline or genny, you should have a second isolator. If you tie your alternator output to your charger output to share an isolator, you are braver than I am.

An advantage of an isolator is that with dissimilar cell technology, you have a separate charging output that might be able to be separately conditioned to protect the high-tech cells

The ACR installation instructions show that you can wire an LED to indicate the "joined" condition, and can add a Boost/Normal/Disable toggle switch. The "Boost" command will force a join provided either battery bank measures over 9 volts. The "Boost" function could be used with careful monitoring while going down the road to stop the make/break events while a very weak bank charges back up.

So, to share a charging source, our choices are:

1. A heavy-duty battery disconnect switch from plus on one bank to plus on the other, operated by a smart operator. No voltage drop or power used anywhere, but if left on can result in both systems becoming discharged.
2. A solenoid joining plus to plus, operated by a smart operator via a remote switch as in # 1 above.
3. A solenoid from plus to plus powered from the ignition accessory circuits, which connects whenever the bus is in the "run" position. This assumes the alternator is running whenever you leave the key on.
4. An ignition solenoid as in # 3, adding a Force on/Disable/Automatic toggle switch. Turn off the solenoid feed from the key if you're troubleshooting the wipers, or the kids are playing the driver's radio, etc.
5. An ACR from plus to plus in automatic voltage sense operation.
6. An ACR from plus to plus with the mode switch added.
7. An isolator that steers alternator power to the lower voltage battery system (or both if near equal).
8. Two isloators, one for an AC-powered charger, and one for the alternator.

I personally would probably not choose an ACR, I probably would use either a battery switch or an isolator. So far, we always dry camp, and I don't like the idea of any extra battery draw. Also, the contacts will eventually wear out.

If I were using a solenoid, I would probably use a plain-Jane one from NAPA or Tractor Supply, so if (when) it went bad I wouldn't have to find an RV dealer or Camping World to be back in business. I would probably wire it to the key with an override switch as in choice # 4.
__________________
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
Redbear is offline   Reply With Quote
Old 05-24-2008, 08:56 PM   #18
Skoolie
 
odyssess's Avatar
 
Join Date: Mar 2007
Location: Las Vegas, Nevada
Posts: 109
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: T444E 3800
Rated Cap: 36
Re: How do you choose the battery isolator size?

Since I already have the isolator, I want to know if mounting it sideways will be an issue. The instructions say to mount it so the cooling fins run vertically and attached to metal. I can attach it to metal, but there is nowhere close to the alt or batteries that I can mount it vertically. It's a cool spot under the bus away from the heat of the engine, but would this be bad and if so, how bad? I have a 145 amp alt and a high performance norco 200 amp isolator, so it wouldn't be too much for the isolator to take(hopefully not heating it up as much.) Thanks
__________________
http://www.skoolie.net/gallery/v/Skooli ... Green+Bus/
Keep on Keeping on.
odyssess is offline   Reply With Quote
Old 05-25-2008, 10:49 AM   #19
Bus Crazy
 
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,096
Re: How do you choose the battery isolator size?

I haven't seen a picture, and its just my opinion, but Ithink you should be fine.

Remember. 145 amps is the PEAK output of the alternator, only available at higher RPM with either a very discharged battery or a full DC load (driving in a blizzard with all lights, wipers, and heater going while dinner cooks in the microwave running on an inverter. ). You are not going to put that much current out at idle, even if it's needed. I'd be surprised if the AVERAGE current on a long daytime drive was over 100 amps.

The isolator, if the manufacturer was conservative, should be able to withstand more than 200 amps continuous to either battery system, with proper airflow. If the manufacturer was cheap, he may be expecting the duty cycle to be low and put higher numbers on a lower capacity unit, counting on the fact that it won't be stressed except occasionally. Either way, you already have 27% reserve capacity built in, before you consider the reduced duty cycle.

As far as fin position, the unit will get a little better cooling if the air passes between the fins (along their length) instead of hitting the first one at right angles and then passing the tips of the others. The vertical orientation is good for installations that stand still (like in a closet), where the only airflow is convection from any inverter heat. If your "under the bus" mounting is on the frame, the front-to back movement of air as you travel is greater than any inverter-created convection would ever be. Mounting it vertical there would be counter-productive. Mounting the isolator to metal will cause some of the heat to conduct away from the fins, making the mounting a part of the heat sink.
__________________
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
Redbear is offline   Reply With Quote
Old 05-25-2008, 12:46 PM   #20
Skoolie
 
odyssess's Avatar
 
Join Date: Mar 2007
Location: Las Vegas, Nevada
Posts: 109
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: T444E 3800
Rated Cap: 36
Re: How do you choose the battery isolator size?

Seriously, it's scary how good you are with electrical stuff. I'm really glad you are a part(BIG PART in my opinion) of this community. I get better, faster answers from you(as well as others) than going down to the R.V. supply store!! Thanks again Redbear!!!! I'm going to install that Isolator today.
__________________
http://www.skoolie.net/gallery/v/Skooli ... Green+Bus/
Keep on Keeping on.
odyssess is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How did you choose your bus? That Guy in Maine Conversion General Discussions 8 01-18-2014 10:54 PM
For Sale - NIB battery isolator, 240 amp bodaver32 Classifieds | Buy, Sell, Swap 1 12-12-2011 09:19 AM
How to choose a bus? huggyb1972 Everything Else | General Skoolie Discussions 2 09-03-2010 09:45 AM
how to choose what size RV furnace? dentedvw Conversion General Discussions 1 03-13-2010 01:27 PM
Main Battery - Starting Battery Group 31? 8D? Tone Conversion Tutorials and How-to's 5 04-16-2009 06:02 PM

» Virginia Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 06:06 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.