need an Electrical engineer to explain this, jump box Options

[r_towle]

Hi,
I have a 997 (this feels like the start of a support group thing)

This car has an electric front hood latch.
So, the battery needs to be hooked up to open the front hood where the battery is...
Its not logical, but Porsche put in a shortcut.

So, go to the fuse box inside, pull out a red lead, and hook up a 12VDC battery to this lead, and chassis ground...
Hood opens.

Instead of using a full size heavy car battery, I went and bought a lithium battery "jump box" thing
Schumacher SL1639 Lithium Portable Power Pack and 1000A 12V Jump Starter

So, it will not work.
We ended up getting a full size battery, with jumpers, just to open the hood, so we could reconnect the battery.

My question is...WHY does it not work?
When I put my meter on it, I see 16VDC
ITs fully charged.
Its on.

The Tech support told me the unit can only be used for jump starting a car.
The mechanic at the shop told me he also had this issue, and the unit needs to see a load??

I will return this if it will never work...but I really need to know why it won't work.
I can get a motorcycle battery, or some other unit that will take care of my needs...but this thing should work...yet it does not.

Anyone care to explain electricity to me?

Rich

[mgphoto]

2 words Ohms Law.

[worn]

2 words Ohms Law.

I raise you with ROYGBIV. I guess that the jump pack is supposed to drop a lot of power against a relatively low resistance. The circuit to open the trunk might not meet the sensor’s expectation, and the jump pack will not fire. These lithium batteries aren’t just batteries. They come with brains meant to prevent usefulness. I wonder if a nine volt battery would do the trick. I have a stack of useless Amazon batteries for tools. I cannot charge them, but expect they could be charged if the defective chips would let them.

[r_towle]

Sorry….I read ohms law and I don’t get why this jump pack won’t work, yet I see the voltage with a meter.

I guess I will return it and get a small lawnmower battery or similar

[914GT]

Do you see 16v with it attached to the load? I suspect the voltage is dropping too low as the supply can’t provide enough current to drive the solenoid. Or as mentioned above a current limiting circuit is involved.

[76-914]

Rich, buy a 12v cordless drill battery or 8 flashlight batteries.

[r_towle]

Rich, buy a 12v cordless drill battery or 8 flashlight batteries.

I will tomorrow…so I can open the trunk again (IMG:style_emoticons/default/smile.gif)
Terrible design.

[r_towle]

Do you see 16v with it attached to the load? I suspect the voltage is dropping too low as the supply can’t provide enough current to drive the solenoid. Or as mentioned above a current limiting circuit is involved.

Honestly, for $120 buck…it’s a heavy flashlight …
Bringing it back tomorrow.

[mepstein]

The jump packs are really great in the usual situation you buy them for. We use one at the shop all the time. Porsche’s always seem to have a dead battery when they need to get on the trailer. I bought one for my daughter after she had to deal with a dead battery and no good way to get close with jumper cables. We got AAA to tow it but a jump pack would have fixed it.
Worth their money X 10 when you really need it.

[r_towle]

I have larger jump packs..

I wanted something light and small to open the trunk multiple times while I move this car around with no engine…and main battery unplugged.

Sadly, I only have an open trailer, so the hood must be closed.

I will get something small tomorrow.
We have a store nearby named “batteries plus”
They will have something…

[bkrantz]

Not sure about 997s, but my 991 has a hidden pull wire attached to the front latch, in addition to the fuse box jumper thing. The pull cable can be found hiding behind the front left fender liner. Some people relocate this or add an extension so they can pop the frunk lid without removing the fender liner.

[r_towle]

Yes we found and tested that pull.
Can you imagine a few scenarios…
Dead battery at night…wheel locks on car, tools in trunk.

How about dead battery and a tow truck driver…who has no clue about the front trunk jumper.

Sorry, but it’s just a dumb design.

[theer]

Rich- I had the same thing happen to a friend’s 911 (I only run with the crowd owns these fancy-pants cars, don’t have one myself.). Anyway, I used a regular jump pack - the big heavy one- and it worked fine.

I have also used the same jump pack to run the 12v winch on my car trailer. Works fine for that, too. Maybe the little lithium ones have some kind of security/safety BS thing to protect it…?

[Geezer914]

12V alarm battery or 12V lawnmower battery.

[StarBear]

The jump packs are really great in the usual situation you buy them for. We use one at the shop all the time. Porsche’s always seem to have a dead battery when they need to get on the trailer. I bought one for my daughter after she had to deal with a dead battery and no good way to get close with jumper cables. We got AAA to tow it but a jump pack would have fixed it.
Worth their money X 10 when you really need it.

(IMG:style_emoticons/default/agree.gif) Yep; have one in each of our regular cars. Have to remember to keep it charged up, though! On the first of every even month. Put one in Frogger for the NE Gathering trip.

[Front yard mechanic]

My cheap hf battery charger has a chip in it it has to sense a load drop before it will kick in. Try to find a jump pack that has instant on.

[GregAmy]

My cheap hf battery charger has a chip in it it has to sense a load drop before it will kick in.

Yup. You probably need one that has a 12V cig plug to do what you're trying to do.

I'm guessing 5V from the USB ain't gonna be enough.

[Superhawk996]

Maybe the little lithium ones have some kind of security/safety BS thing to protect it…?

The thing everyone loses sight of is that Lithium-ion batteries are not “just” a battery.

Lithium ion batteries are volatile. As such, almost everything except a raw cell has a battery management system to protect them from being fully drained below 10-20% of capacity. Likewise they are protected from over charging. They are protected from short circuits. Lithium-ion batteries can self oxidize (I.e burn) due to thermal runaway if the cell gets too hot from being charged or discharged to fast. This is all done by a microprocessor (and other electronics) controlling the battery. Even single cells can have a very simple battery management system on them.

If the battery management system wants to limit current in or out it can do so. In your case, current is being limited until it sees a load that looks like a battery (connected proper polarity) and a low resistance load like a starter motor.

Not just a battery.


https://lygte-info.dk/info/battery%20protection%20UK.html

Note: mechanical engineer but don’t hold it against me - I play with electrons too!

[bzettner]

Yes we found and tested that pull.
Can you imagine a few scenarios…
Dead battery at night…wheel locks on car, tools in trunk.

How about dead battery and a tow truck driver…who has no clue about the front trunk jumper.

Sorry, but it’s just a dumb design.

(IMG:style_emoticons/default/agree.gif)

My 986, of course, has the emergency pull wire. I relocated mine into a place that can be reached thru the air dam. It's saved me several times.

(IMG:style_emoticons/default/beerchug.gif)

[jd74914]

Maybe the little lithium ones have some kind of security/safety BS thing to protect it…?

The thing everyone loses sight of is that Lithium-ion batteries are not “just” a battery.

Lithium ion batteries are volatile. As such, almost everything except a raw cell has a battery management system to protect them...

(IMG:style_emoticons/default/agree.gif)

Those protections are there for good reason.

Some jump boxes (looking at you Noco Genius) have override buttons so you can start a battery-less car with them. The button is a tacit user acknowledgement that the situation is appropriate for the given use. In any case, they work pretty good for things like starting diesel tractors missing a battery, etc.