Bus Conversions dot Com Bulletin Board
December 22, 2014, 09:41:56 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: If your computer is lost, damaged, or stolen, your Online mags will be safe.
   Home   Help Forum Rules Search Calendar Login Register BCM Home Page Contact BCM  
Pages: [1] 2  All   Go Down
  Print  
Author Topic: pressure switch  (Read 2126 times)
Skykingrob
Full Member
***
Offline Offline

Posts: 234




Ignore
« on: December 13, 2013, 08:27:36 PM »

I am wanting to charge the house batteries from the DN 50 alternator when the engine is operating. I have the line run but not yet connected to the house battery bank. I need some kind of pressure switch that will close to allow the current to go from the alternator to the batteries. I do not know which is best, air or oil, but think it would be easiest with an oil switch. I do not what to look for. Please give me a link or specific name/number of an oil pressure switch that would work on a 8v92 whose standard oil pressure is 15-25 psi and an alternator whose output could be as much as 250 amps. Please also give me the name of a electrical switch that can tolerate the amount of current from the alternator and can be triggered to close by a signal from the oil pressure switch.
I did search the archives but did not find anything, most likely because I didn't know what to search for.
Thanks

Rob
91 XL 40
Missouri
Logged
luvrbus
Hero Member
*****
Online Online

Posts: 13133




Ignore
« Reply #1 on: December 14, 2013, 02:44:06 AM »

A regular oil pressure sender will work but I only seen the hookup used with a relay www.texasindustrialelectric.com  they can help and may have what you are looking for

good luck
« Last Edit: December 14, 2013, 02:49:34 AM by luvrbus » Logged

Life is short drink the good wine first
eagle19952
Hero Member
*****
Offline Offline

Posts: 1390




Ignore
« Reply #2 on: December 14, 2013, 08:33:48 AM »

You will (should) need a relay/contactor....
I know of no sender unit that will carry charge amps by itself.
Logged

Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 NA, DDAllison on 24.5's 12kw Kubota.
Wants Paint Smiley
Previously owned by Wee Willie Ent.
Lee Bradley
Hero Member
*****
Offline Offline

Posts: 721




Ignore
« Reply #3 on: December 14, 2013, 09:31:15 AM »

Why do you want to switch the alternator output?
Logged
Cary and Don
Hero Member
*****
Offline Offline

Posts: 674




Ignore
« Reply #4 on: December 14, 2013, 10:10:55 AM »

Why not use a battery isolator switch?  Bus generator to the input,  bus batteries to one output, house batteries to the other output. Works great on our system.

Don and Cary
Logged

1973 05 Eagle
Neoplan AN340
bevans6
Hero Member
*****
Offline Offline

Posts: 4883


1980 MCI MC-5C




Ignore
« Reply #5 on: December 14, 2013, 10:15:52 AM »

Switching the alternator connection to the house batteries is a simple and easy way to automatically charge the house batteries from the alternator yet ensure that the start batteries are not drawn down by extended house usage.  A 5 psi pressure switch connected as the signal for a high current relay would work, you may need to have the pressure switch connected by a small relay before the big relay, you need to research the pull-in current of the high-amp relay coil.  My MCI has such an oil pressure switch as stock on the pressure manifold, it usually lights up a tell-tale light on the dash.

There is a side-effect to doing this with an oil pressure switch.  It needs to be a low enough pressure switch so the relay isn't cutting out whenever the engine idles.  Cranking the engine over will normally produce enough oil pressure in two or three seconds to operate the switch.  At that point you would see the house batteries switched into parallel with the start batteries, which you may not want.  I personally wouldn't use an oil pressure switch, I would use an air pressure switch as stock on the MCI.  It is used in my bus to turn the alternator on when air pressure is up to 70 psi or so, it could easily also switch the house batteries into the circuit.  Another caution, though.  It's very possible for the house batteries to be quite discharged.  The start batteries will also be a little discharged, having just started the bus.  If both sets of batteries are hooked to the alternator simultaneously then the current draw can spike to very high, with the resulting load on the alternator drive system peaking.  If your drive gears are weak at all, this will put the highest load on them and possibly instigate a failure.  I know that on my belt drive alternator, with 4 well tensioned belts, the current load when that happens can cause the belts to slip and squeal until I switch the house batteries out of the circuit.  For this reason I have implemented a manual switch system so that if I know the house batteries are drawn down a lot I can let the start batteries charge for 5 minutes before I switch the house batteries onto the alternator.

Brian
Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
gus
Hero Member
*****
Offline Offline

Posts: 3546





Ignore
« Reply #6 on: December 14, 2013, 02:05:00 PM »

Your best bet is a simple relay and toggle switch, then you are independent of any pressure system and can switch when you want - like adding on the house batts for an emergency start with weak start batts.

Keep it simple!

Even simpler is a battery disconnect switch on each batt, but that means you have to go outside to make the switch. There should be a disconnect on each batt anyway for emergencies - been there -  stuck start solenoid!!
« Last Edit: December 14, 2013, 02:08:28 PM by gus » Logged

PD4107-152
PD4104-1274
Ash Flat, AR
Skykingrob
Full Member
***
Offline Offline

Posts: 234




Ignore
« Reply #7 on: December 14, 2013, 03:21:33 PM »

Thanks for the ideas guys, keep them coming. I wondered about the demand on the alternator when the oil pressure reaches the cut in pressure and as Brian says, that may be a failure point. That is why I was using some kind of pressure switch, to keep the alternator from going from doing nothing to full work load in short order charging both the start and house battery systems. Likewise, I thought the air pressure switch could cause an undesired effect in that while there is air pressure, the systems, house and start batteries that is, would stay connected even though the coach is not running which could lead to the start batteries draining.
I like the idea of a high current relay like those Clifford mentions from TI and the toggle switch Gus mentions is certainly simple but the same problem exists in that if I forget to shut off the toggle switch, the two systems are connected resulting in the start batteries possibly draining down. However, that is only true if there is not a diode in my battery isolator system which like Don says, is how his is set up. I will check to see if there is a diode in my battery isolator but in the meantime, Don, how is yours set up and what brand battery isolator do you have?

Rob
91 XL 40
Missouri
Logged
Cary and Don
Hero Member
*****
Offline Offline

Posts: 674




Ignore
« Reply #8 on: December 14, 2013, 05:20:40 PM »

We have a toggle switch that operates a relay that will let our house batteries charge while running.  It is energized by a circuit that is hot only when the run switch is on.  Turn off the engine and the circuit is off.  This is in addition to a jump start circuit that runs on a momentary switch.

Don and Cary

Logged

1973 05 Eagle
Neoplan AN340
Lin
Hero Member
*****
Offline Offline

Posts: 4604

1965 MC-5a




Ignore
« Reply #9 on: December 14, 2013, 05:40:25 PM »

Just to chime in.  I agree with Gus, Don and Cary and others that use/suggest a dash toggle energized through the master switch for this job.  Sometimes automatic is better but since one can conceive of situations when you would want control here, it is better to have a manual switch.
Logged

You don't have to believe everything you think.
belfert
Hero Member
*****
Offline Offline

Posts: 5480




Ignore
« Reply #10 on: December 14, 2013, 08:40:31 PM »

I charge my house batteries from the alternator using a circuit that was originally for the A/C unit.  This circuit only has power if the engine is on and the alternator is working.  I added a solenoid with a switch on the front dash so I can turn off the power if I need to reduce load on the engine.
Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Jerry32
Hero Member
*****
Offline Offline

Posts: 727





Ignore
« Reply #11 on: December 15, 2013, 05:50:40 AM »

Manual switch works for me and also helps if you need a boost on start. Jerry
Logged

1988 MCI 102A3 8V92TA 740
Jon
Sr. Member
****
Offline Offline

Posts: 268




Ignore
« Reply #12 on: December 15, 2013, 06:08:25 AM »

Rob,

I think the 50DN has a relay output post. If it does then a simple way to send juice to the house batteries is to use a solenoid such as the firewall mounted ones found on old cars. They are available from NAPA, are cheap and when the alternator is not putting out power the solenoid opens so the two battery banks are not tied together.
Logged

Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
luvrbus
Hero Member
*****
Online Online

Posts: 13133




Ignore
« Reply #13 on: December 15, 2013, 06:20:07 AM »

Just buy the right stuff I have a friend that stops here every year and we change out his relay some here call a solenoid you cannot convince this guy a 50amp continuous duty relay (solenoid) he pays less than 20 bucks for will last with a alternator putting out 250 amps charging the house batteries 

The 6 years I know of him replacing the relay he could have bought one that would carry the load
Logged

Life is short drink the good wine first
gus
Hero Member
*****
Offline Offline

Posts: 3546





Ignore
« Reply #14 on: December 15, 2013, 09:27:07 AM »

A relay to a toggle switch carries a very small load, insignificant actually, so that is not a problem.

My method is to drive a while to let the starts get a little charge before connecting the house batts. However, with a 300 amp alt that is probably not necessary!
Logged

PD4107-152
PD4104-1274
Ash Flat, AR
Pages: [1] 2  All   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!