Be attentive during jump starts

seans

Member
When getting help with a jump start, be aware that some of the jump starting battery boxes out there are configured to supply either 12V or 24V, and that it is quite easy for those manning the boxes to accidentally reverse the polarity or set the output voltage improperly.

I let my van's battery voltage drop to 11.4 volts recently, which was not enough to turn over the starter. When the starter engaged the battery voltage obviously sagged well below that needed to keep the electronics happy (in fact it caused the radio clock to reset to 12:00). At one point I noticed a "START ERROR" briefly appear in the instrument cluster.

The long term parking lot I was in offered a free jump start service. This was performed by a lot attendant who was not a mechanic.

After signing a waiver, I watched carefully as the attendant pulled a jump starting device from his pickup truck. This was basically a box with jumper cables and obviously a couple of large gel cells inside.

The first thing he did was try to connect the positive jump start cable to the negative battery post. He had not connected the second cable yet, so there was no need for a panic response, and he noticed his mistake just as I was about to point it out to him.

The second thing was that I noticed that his jump start box had a switch with three positions: off, 12V, and 24V. He was hooking the cables up with the box set to 24V and I had to point out to him that this was the wrong setting. He did not change it right away so I changed the switch position myself. Had the box been turned so that the switch was not been facing us, he would have made the connection without either of us noticing.

At the time, the thought crossed my mind, "why would this be left at 24V? What are the odds the last vehicle had a 24V system?" Now as I reflect on it, I realized that he may have been jump starting everyone at 24V, as a dead battery will accept current much faster at this higher voltage setting and it will certainly make a starter turn a bit faster!

The van's battery needed a few minutes to soak up some of the current from the starting box before it would start. I actually did not expect the box to deliver enough current to heat the glow plugs AND let the van start, but it did.

Perhaps it is errors made during jump starts (incorrect voltage, reversed polarity) that have led to the admonitions I've seen in the forums not to jump start Sprinters?

Sean
(cross-posted to sprintervan Yahoo! group)
 

Johan Turbo

New member
Also be carefull when you jumpstart by another vehicle. Putting the cables on is no problem. Before detaching the cables put on the lights and other electric consumers on both vehicles. The sudden drop of current cam make an induction that can harm electonic components. Putting on all the lights smoothens the induction.
I never use those boxes. Most of them are a great risk. I prefer a real battery or another vehicle.
 

Top Bottom