04-24-2010, 08:52 AM #1
- Join Date
- Apr 2010
Simple starting / shutdown question
Looking for opinions, this is one of those questions that will have many different answers I'm sure. I teach my new drivers to shutdown as many electrical items as possible before shutting down the truck (headlights, fans, A/C, ect), thus allowing for as little current draw as possible for start up. Many of the other guys seem to think this doesn't matter as there are generally 4-6 batteries to handle the load. What do you think?
04-24-2010, 09:46 AM #2
- Join Date
- May 2006
- Bryn Athyn, Pa.
Here are some caveats, though. I do get concerned where motors under load are involved. A motor, especially a DC motor, draws its maximum current when it is beginning to turn and to overcome the inertia of whatever it's turning. When you go to start the engine, the starter imposes a huge load against the battery system, enough to reduce the voltage throughout the entire electrical system. That, in turn, increases the current draw of any other motors that are "on." Over a period of time that could lead to failure of those motors.
In the case of a marginal battery system it could be the difference between starting or a "no start." Here are some of the things that I think of when I say "marginal." Low batteries for any reason (inadequate charging system, both on board and shoreline); loose, dirty, corroded connections anywhere; inadequately sized cables, not enough batteries or batteries that are just to small for the job (watch cranking amp, CCA, etc.). Engines that don't start easily will soon show up any shortcomings in your system.
FireMech, Rescue 101, VanIsleEVT and others may very well want to add to the list.
Our newer engine has 6 Group 31 batteries, the older one has two 8Ds. As long as they are fully charged and all of the connections are tight and free of corrosion, they do the job well. Those vehicles are on custom chassis. But our Special Service truck, on a commercial chassis has 2 Group 31s. It has to be kept after constantly. Battery replacement on it is twice as frequent as on the others.
The Technology and Maintenance Council (TMC) of the American Trucking Associations publishes Recommended Engineering Practices and Recommended Maintenance Practices, which, if followed, can reduce much of the grief and woe that we encounter. As a member, I get these regularly. You don't have to be a member to buy them but they are quite expensive. I don't know if any public libraries would have them. If you can get at them, they're worth reading and considering. We referenced the REPs extensively in the specs for our last engine.
Even so, there are special conditions that we in the emergency services impose on our vehicles that are not addressed there.
The short answer is, in my opinion, you're doing it right. Keep on keeping on!
Last edited by chiefengineer11; 04-24-2010 at 11:04 AM.
04-24-2010, 09:55 AM #3
Anyone with half a brain knows that starting a large truck engine (especially in cold weather) requires all the CCA's you can muster, one battery, two or six.
That being said, do you want to replace those one, two or six batteries every so often, or would you rather extend their lives as much as you can and get your money's worth out of them????? Tell the bone heads to turn off anything and everything un-necessary. Better yet, make it an SOP with punitive action for failure to comply. (You wanna cost us money for new batteries? Ok, don't respond for 15 days.)
As I am sure Chiefengineer11 will comment on, AMBULANCES are murderous on batteries, especially in HOT weather! It was made SOP at our place years ago, that when starting the boo boo box, you did so without turning on the box (we spec all our boo boo boxes with segregated chassis/box systems....) once the engine is started, you may then turn on the box. And when at an incident or hospital and idling, "thou shalt turn off any and all un-necessary devices."
EDIT: I knew he would be around, he typed his as I was typing mine!"Loyalty Above all Else. Except Honor."
04-24-2010, 02:44 PM #4
With all the newer electronic load masters and such, it is a bad idea to shut the rig down with everything on. If you're running your lights to get back inside your bay, turn them off and let the truck idle for a few seconds before shutting down. You can create a spike/surge in the electrical system that can take out some of these sensitive (expensive) electronic components with the system under a heavy electrical load.
The batteries primary job is to start the truck and power the computers that run the engine. After it's started, the alternator takes over to power the rig. With a heavy load on at start up, your taking power away from your starter, and when it is started, also applies a quick and heavy load on the alternator. This will take out the alternator after a while.
I just shake my head everytime I've powered up a rig to find the E-Master on, and all the bells and whistles running. I've pleaded with drivers to turn everything off before shut down and to wait until the rig is running before powering up what they need until I'm blue in the face. Some listened, some learned, and some don't care.
Otherwise, reread what the Chief posted.
FM1I'm the one Fire and Rescue calls, when they need to be Rescued.
Originally Posted by EastKyFF
04-24-2010, 11:44 PM #5
- Join Date
- Dec 2002
- Central NJ
I learned, and therefore teach (for most of the aforementioned reasons) this way of doing it. My vote is stick to the program.
04-26-2010, 02:37 PM #6
- Join Date
- Jan 2007
- Pa Wilds
Leese-Neville heavy duty MS-series starting motors require 9,000 watts at 24 volt starting. This is 375 amps. It will also draw down the voltage produced by the batteries due to internal resistance and wiring resistance. Any electronic controls (strobes, lights, fans, etc.) will then try to pull more amps than normal to compensate for the low voltage. Leaving loads in the "ON" position that could be turned off just adds to the system stress.
04-28-2010, 07:34 PM #7
You could cut off the Emergency Master switch before you shut the engine down. Likewise when you start the truck leave the Emergency Master switch off until you are ready to leave the house on the run.
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