Can't jumpstart - help!

Hi Pat, OK I'll accept that, but, if one is using a comparable battery ( or less) why should there be a +100 Ampere power surge. Or, was that it exactly, the battery he used was more powerful. Even then shouln't the system be only drawing the necesary current to start? Redundant, but in jumpstarting a current surge should not occur. In house circuitry this can occur after a poweroutage because extensive equipment may be left on, did the Op try to jumper with Power on? (but, not know it) ty andy.

 

Of course the battery he was to using to jump was more powerful. He was using it to JUMP START THE CAR. There is always a very big inrush of current when trying to charge a dead battery. Especially if the battery being jumped is stone dead.The more flat the battery is the bigger the initial surge. There's no regulation involved. The dead batt will suck up as much current as the donor can provide especially initially. Its not like a battery charger that is current limited. Which is why so many people damage there Prius with a simple jump start. They do everything right and still there's damage. Lots of delicate circuity that does not like getting slammed. I don't think I would ever jump start my 07
unless I had my Fluke DVM handy and could see how flat the boot was first.

Not sure what you mean by trying to jump with "Power on". How can the system be on if the boot battery is dead?

 

I was thinking, the car was in ready but not showing on the MFD. When using a 150A bat in parallel with the Aux, 32AH, I can understand a current surge, so during the milliseconds before the 100A fuse blew current (high) was drawn forward and blew another fuse in the fuse block. That being the case, it is just too easy to ruin the Prius using an unknown DC battery for a jump start. I agree with you.. So.... one could first diconnect the positive lead on the Aux, and use the bat on hand as a simple charge. ( all on an emergency basis) OR.......Perhaps Prius is way overfused, why 100 Ampere fuse link just for boot-up current, recommended recharge is in the trickle charge level, 2 to 3 Amps, right? The design charge rate on the car should be identical, correct?

 

Hi Andy,

The DC to DC converter output is fused at 100A because the various Prius systems can consume substantial power on the 12V bus. This has no relation to the current required to charge the 12V auxiliary battery.

For example: two PTC electric heaters to supplement cabin heating (~40A just for that system), rear window defroster (probably 20A or so), ventilation fan, headlights, foglights and other body lighting, etc. We haven't even talked about the current demand of the numerous ECUs, the electric power steering, etc.

 

With all the discussion about jump starting, can someone describe or reference an accurate schematic for the wiring/fusing starting at the positive post on the 12 volt battery and ending up at the jump start post at the front of the car. Is there a straight wire to the post with a fuse near the battery? And does the fuseable link in the underhood panel sit between the jump start post and the inverter and the rest of the 12 volt system on the car. I've never seen an actual schematic of this part of the car which would show where the fusing is located and how the 12 volts is routed.

 

I haven't seen a schematic that shows the dedicated jump start terminal. Here's my guess regarding the sequence of components:

12V battery positive terminal -> 120A main fuse located within fuse block on top of the 12V battery positive terminal -> positive battery cable running along the driver's side of the car, leading up to main relay/fuse box -> 100A DC/DC fuse -> DC to DC converter output

The dedicated jump start terminal probably connects to the relay/fuse box side of the positive battery cable and feeds the 12V bus leading to the car's electrical systems. If you take the nut off that terminal and remove the wire, that will disconnect power from the various Prius systems.

 

hmm.... is there a product that can jump a prius - without risking anything (except for reversed polarity) perhaps a "float charger" with a 10amp limit? Would that be enough to jump a prius, if said float charger with a 10amp limit existed?

 

Thanks for the information. That's kind of what I was thinking, nothing but a wire and the 120A fuse between the back and front of the car. Barring a shorted battery its hard to see how a jump from another 12 volt battery at the front causes any really big current surges. Even a single cell short shouldn't draw massive currents. If the battery in the car is dead and not shorted its just like hooking up a new battery after replacement. I guess if your battery is low and you can't shut off the car and its in a partially powered state, a jump could cause currents to flow that don't normally happen as the car powers itself up in its normal sequence.

 

10A current is not sufficient. The Prius requires ~30A for a brief period during startup.

To reduce the possibility of popping the Prius fuse links, one could attach an 80A fuse to the positive jump start terminal (80A being less than the 100A DC/DC fuse link or the 120A MAIN fuse). The reason you need a fuse bigger than 30A is that the dead (or weak) battery will draw substantial current upon startup.

 

I'm thinking that if my Prius ever goes dead in my garage - despite constant use of a VDC Battery Minder - it would be safer to crawl into the back, manually pop the hatch, remove the battery, and fully charge it off the vehicle.

 

Yes with all the complaints of jump damage the best way is to isolate the boot battery and trickle charge it. But always remove the negative lead not the positive. Its just the proper way. Its very easy for your wrench to hit a ground if your taking the pos terminal off resulting in a dead short across the battery. Very exciting. No such worries on the neg terminal.
And as far as your over fuse/trickle charge question...what Patrick said.

 

And indeed, this is Toyota's recommended procedure: to remove the battery from the vehicle and charge it. Then you don't have to worry about damage to the vehicle's electronics and in case the battery blows up while you are charging it, no damage to the hatch interior.

Living in southern CA, ambient temps are moderate. My Prius is driven 25K miles per year so no worries about the 12V battery being discharged due to lack of vehicle use. I plan to replace the original equipment battery next winter as a preventive measure, it will be 6 years old then.

For owners who live in frigid winter areas, I think it would be reasonable to replace the battery at 4 year intervals to reduce the likelihood of a no-start situation due to a weak battery.

 

No. Its not anything like installing a new battery current draw wise. In standby there's very little current draw just standby B+ for all the CPU's. No current draw happens until you "ready" the car.
Charging a very flat car battery has a very large initial current draw especially if the donor battery is in good shape and there's an excellent connection between the 2. The CPU's would especially not like the big arc you get hooking up the jumper leads too. Plus The circuitry may not be designed to see that kind of current. Probably much more than the circuit protection was designed to handle. Its our cars Achilles heel for sure. But if the battery is just a little low like 10 volts and its in good shape a quick jump would probably not hurt. I think its bad though with a really dead battery.I personally would never jump my car though.

 

Very good explanation Pat. As I mentioned before, I experimented using a block spade terminal, 7 AH battery. I disconnected the Prius Aux and jump started at the forward position, shut the car off, moved the block bat to the rear position and then proceeded to drive about 6 miles in one direction and then drove home. Had no problems at all, and block battery serves as a emergency jumper or a temp replacement. I keep it under my seat. I guess I'm a hardhead but I have difficulty imagining a powersurge in the set-up we are discussing, never having seen it occur in battery to battery. But I will accept your explanation and that it can happen. But as edthefox remarked accepting a charge from a larger source, with the Prius being ultra low could be a Prius disaster. It is strange that Toyota hasn't worked aroud this? Maybe that was Ginny's problem? Reverse polarity was never verified.:cheer2: ty andy

 

Hi Peaquod,

Thanks for your update in post #34. Referring back to your post #13, and given the blown ETCS and Dome fuses, does this imply that you had (inadvertently) reversed polarity during the jumpstart? I'm wondering if you can clearly recall what happened there.

Yes, my 2004 is logging lots of miles. It was owned for the first three years by my dad who put 15K miles on it total. After I bought it, we added 52K miles over two years and the odometer is now at 67K.

 

The discussion here suggests that there are other ways to bother the Prius besides a reversed jump. In light of that, one might suggest that adding a jumping point under the hood is an attractive nuisance?

I would like to know if adding a large diode for reverse polarity protection might also protect against the big-surge scenario. My EE skills are too small to know.

 

All very good posts by everyone here. That said, I would offer the following:
1. His 100A fuse may have blown due to an obvious surge. That surge may have been due to a shorted cell or two in his battery. He reported a terminal voltage of 9V. That's more than 3V below what it should be, so I suspect 2 shorted cells.
2. Toyota recommends jumping in the engine compartment but that is obviously not always the best way. So I would recommend (if possible) to jump right on the battery itself. But before jumping, I would check the terminal voltage. If that is between 10 and 11V, then a jump may be successful. If it is lower then jumping is not recommended. Reason: if you have a shorted cell or two, then the act of connecting a jump source will cause a heavy current flow into the bad battery. If left on long enough, things may start to heat up! Danger... Danger... Will Robinson! So, if the terminal voltage is low, I would highly recommend pulling the battery and replacing it.

Not everyone will be able to jump at the battery terminal and that is why Toyota provided the underhood terminal.

 

Hi Doug,

An add-on diode attached to the dedicated jumpstart terminal would do nothing regarding current surge. Assuming that the car was properly jumped but the 100A DC/DC fuse link still popped, that would be because the 12V auxiliary battery was in such bad condition that it sucked up more than 100A of current from the 12V bus.

There are two fuses between the DC to DC converter output and the 12V battery: the 100A DC/DC fuse link that lives in the 5" long white/clear plastic box within the main relay/fuse box, and the 120A MAIN fuse sitting on top of the 12V battery's positive terminal.