Jump Posts and General Electrical and Fuel Safety Questions

[Mark_M]

Good morning everyone. I recently installed the battery into the floor of the trunk and and while I was in there I also put in some external charging posts as well. Still working through getting everything to fit in the battery box and attaching the charging posts to the battery terminals (may need a longer nut on the positive battery terminal, unless anyone has other suggestions on wiring).

My question is safety, which is paramount for me on this build. I want to minimize any chances of electrical (or fuel for that matter) fires. What should I do to limit the chance of an electrical fire in this type of set up or with a Roadster build in general?

For a little more information, I have a heavy duty starter solenoid also located inside the trunk behind the passenger seat.

Thanks,
Mark

[michael everson]

Purely from a safety stand point, I would start over. Mount the battery in the front. Eliminate the jump posts and the starter relay. Run the positive battery cable directly to the starter. Most starts have a solenoid already built in. If not then I guess you will need one. The idea is to keep the positive cable as short as possible and with as few connections as possible.
Breeze Automotive (vendor on this site) sells a nice front battery mount.
Just my opinion after 60 something builds.
Mike

[Jeff Kleiner]

My thoughts echo Mike's. When possible I build with a front mounted battery. To me jumper posts are an invitation to disarster and completely unnecessary (my own roadster has sat idle for as long as 6 months and never needed a charge or jump in 10 years).

Jeff

[Mark_M]

Thanks for the quick responses guys. I suspect the reason it was mounted in the back is because of space concerns. The Breeze battery mounting doesn't work for a 385 series big block and I don't really want to pull the engine! Maybe I could make something else work in there but as you can imagine the space is tight. If I keep it in back it sounds like it would be wise to ditch the jumper posts? Assuming it stays in back, anything else i should do to increase safety?

Thanks!
Mark

[michael everson]

run the positive cable through some heater hose or similar.
Mike

[Mark_M]

Thanks Mike. I will do that for sure.

[Just puttering]

Use a 12 v circuit breaker at the battery. If anything ever shorts out, it opens and you dont have melted wires or worse.

[AC Bill]

Adding a battery master switch that you can reach while seated in the cockpit, is a common safety & anti-theft feature, that many builders do.

[Frank Messina]

I agree that external jumper posts are out but I'm going to respectfully disagree as to the location. I'm not saying front mount is wrong but rear mount isn't wrong either and just as effective electrically if properly spec'd as front mount. In addition you're not dealing with an ugly battery in a space you may want for something else. I mounted mine under the trunk floor with 1 gauge cable to the master cutoff behind the front seat and then to the mini starter with no external solenoid. Block and battery grounded robustly to the frame. I got 11 years of faultless service from this setup and only changed the battery because it was getting long in he tooth. Also I would not add fuses or anything else to the circuit that will just complicate your life. Keep it simple.

Frank

[DVANSLEEN]

I don't understand why the jump post are dangerous if installed correctly and covered with the rubber caps. I mounted the battery under the trunk floor with access from inside the trunk. #2 cable to a GOOD cutoff switch and then to a mini starter. Also jump post mounted in the trunk. 19 years on the road,40K miles, on my third battery. No hot start problems. Real happy!

[Frank Messina]

I didn't want a battery box so I built a cage instead .
http://thefactoryfiveforum.com/attachment.php?attachmentid=72931&d=1503968016

Semi Finished
http://thefactoryfiveforum.com/attachment.php?attachmentid=72949&d=1504020750

Frank

[mia65cobra]

Many cars come factory with jump posts, as long as they have covers and you always have them in place when not in use you should be good :)

[weendoggy]

I agree that external jumper posts are out but I'm going to respectfully disagree as to the location. I'm not saying front mount is wrong but rear mount isn't wrong either and just as effective electrically if properly spec'd as front mount. In addition you're not dealing with an ugly battery in a space you may want for something else. I mounted mine under the trunk floor with 1 gauge cable to the master cutoff behind the front seat and then to the mini starter with no external solenoid. Block and battery grounded robustly to the frame. I got 11 years of faultless service from this setup and only changed the battery because it was getting long in he tooth. Also I would not add fuses or anything else to the circuit that will just complicate your life. Keep it simple.

Frank

2nd here. 18yrs with a battery mounted under the trunk in a battery box (my design) with IRS. Cutoff switch behind seat to starter on engine. No charging ports and no heater hose to encapsulate it. If in doubt, put the cable in some harness material, much easier to deal with.

[weendoggy]

Many cars come factory with jump posts, as long as they have covers and you always have them in place when not in use you should be good :)

True. Check most BMW's. We have a 325ci with a huge battery in the trunk (hard to access) and it does have a terminal in the engine compartment for jumping. Also, it has NO heater hose around the cable to protect it.

[BEAR-AvHistory]

True. Check most BMW's. We have a 325ci with a huge battery in the trunk (hard to access) and it does have a terminal in the engine compartment for jumping. Also, it has NO heater hose around the cable to protect it.

Agree. The rear battery front jump posts are standard across the BMW lineup....have been for years.

[NAZ]

The location of the battery can be a safety concern but not just because it's mounted in the rear or under a floor. Same with jumper posts -- just because they exist doesn't make them dangerous. They pose no greater risk than the battery posts or the lugs on a starter solenoid that we've all worked around for many years and somehow haven't caught our hair on fire.

There are a multitude of "hazards" associated with our vehicles and all need to have some form of mitigation to reduce the hazard to an acceptable level. There are plenty of valid reasons for mounting a battery in the front and just as many for mounting it in the rear. There are also many examples of batteries mounted in either location that pose no greater risk. Mark, mount your battery where it makes sense to you. And incorporate any or all of the mitigation suggestions above that also make sense to you. There are other hazards you'll encounter during a build that are far greater than the risk posed by a battery so reserve some energy to deal with these too. And have fun along the way.

[Jim1855]

I'm in the construction phase so no driving experience w/ FFR. But Superformance cars have the battery in the trunk (driver's side behind the rear wheel) w/o problems. Big wire, 0 or 1 gauge, going forward with a short ground to the frame. The battery is hidden in a molded in fiberglass box with a plastic cover. Many owners put a cutoff switch in the ground circuit at the back of the car. The back location also made wiring a hot line to the fuel pump real easy and short, they used the "normal" fuel pump wiring for a relay.
I'm looking for locations to help better balance my Challenge car, will probably go into the passenger side of the trunk but not sure exactly where.
Jim

[Wt4Go]

Cadillac"s have been putting the battery under the rear seats for years. They have a post under the hood for jumping.
Jim

[Mark_M]

Thanks everyone for all the feedback. So many different ways to do these cars, but always great to hear people who have actually done them and get their experience.

[mikeinatlanta]

Me thinks folks should focus less on battery location and more on quality componentry installed correctly. Just sayin.

[Bobby Doug]

Me thinks folks should focus less on battery location and more on quality componentry installed correctly. Just sayin.

Well said.

[smithbks]

Regarding jump posts, isn't it true you can jump the car through other locations? For example, the solenoid. I know it works for trickle charging the battery.

Can you guys confirm that? If so, is there even a need for the posts at all?

[NAZ]

There seems to be a lot of concern over the use of jumper posts. In my opinion, using jumper posts is a no brainer in any application that the battery is installed in a hard to reach location.

You can jump start a car with a dead battery by connecting a good battery's positive pole to any positive terminal that the cable is of sufficient size to carry the load to the starter of the car being jumped. And to make a complete circuit this also applies to the ground side as well. So yes, you can attach the jumper cables to the large positive lug of a starter solenoid. However, properly installed jumper posts are typically safer and more convenient to use for this purpose.

If you want the safest way to charge or jump start a hard to reach battery, install a properly sized battery cable connector such as #7043K7 (without the optional handle) as sold by McMaster-Carr. You can hide it under the car or some other convenient place out of sight. You'll need a set of jumper cables with a mating plug. And you will want to install a cover #7043K281 on the plug installed on the car when it's not in use. I've used these on several vehicles that I've placed the batteries in hard to reach places. I also power my trailer winch with my truck using these connectors.