Automotive/jump starting

Advertisement

Expert: - 3/19/2008


Question
Hi, i have got a 24volt (2 batteries)truck that sits around doing nothing for most of the time, once it is started it will start everytime allday, i have been told that i can jump start my 24 volt truck using my 12 volt truck but not quite sure how to do it correctly, Can you help?

Answer
I would imagine that a workable approach would be to determine which of the two batteries in the twenty-four volt system has less charge (which does translate to to less voltage with lead-acid batteries) at the time you need to do the jump start, and to connect your twelve-volt system across that battery only.  The only caveat would be to ensure that your vehicles are otherwise isolated from each other completely - ie: bumpers not touching - if you are using the 12V system to jump the positive-end battery of the 24V pair; not doing so could put a low-resistance shunt across the lower battery in the pair.

If both batteries are quite flat, then patience will be the key.  First connect your 12V vehicle to one battery and then run it for a time to charge that battery.  Then, disconnect your vehicle from that battery and reconnect to the other battery, and run it again for a time to charge the second battery.  Again, be sure that the two vehicles are otherwise isolated from each other!  After both batteries are sufficiently charged, start the 24V vehicle.

Finally, under-hood-type sealed automatic battery maintenance chargers are very cheap these days - I buy them for as little as twenty-five dollars each.  The outputs are fully isolated from the AC input (as is the case with most chargers), so installing two and connecting one across each battery will be no problem.

While I usually pay cash, I am always happy to provide advice on effective charging!

Cheers ... EGK

Automotive

All Answers

Answers by Expert:

Ask Experts

Volunteer

Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

©2012 About.com, a part of The New York Times Company. All rights reserved.