Car battery jump starters - portable? plugin?

Forums › Transport (cars, bikes and boats) › Car battery jump starters - portable? plugin?

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1943 posts

Uber Geek

#1899240 11-Nov-2017 13:12

BlinkyBill: Well...yeah. But how do I know when it reaches 100%? I mean, this is pretty much why I asked the question in the first place.

Sideface: Cheers, mate, that answers my question

Aredwood: Thanks for the info but I have no way of accurately quantifying current or capacity. I'll just give it another much longer charge - 24 hours maybe.

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Mighty Ape

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TLD

880 posts

Ultimate Geek

#1899262 11-Nov-2017 14:43

I got caught out with a flat battery in my 3.5L petrol Pajero a couple of years ago, and a buddy pulled one of those little jump starters out of her glove box. It's about the size of two hard drives, and I totally thought she was joking, but it actually got my truck started! I'm guessing they work with high voltage and clever regulator to get the current from such a small package, but it really worked. My friend said that the device had already got another vehicle started since it was last charged up, and was doubtful it would start the Paj. I'd have got one myself for those just-in-case moments, but the >$200 p[rice put me off.

http://www.supercheapauto.co.nz/Product/Calibre-12-Volt-Mini-Jump-Starter-3300mAh/366282

Trevor Dennis
Rapaura (near Blenheim)

tripper1000

1539 posts

Uber Geek

#1899279 11-Nov-2017 15:56

geekIT:

BlinkyBill: Well...yeah. But how do I know when it reaches 100%? I mean, this is pretty much why I asked the question in the first place.

This can get a bit technical, but essentially, your battery needs to sit at 14.4 volts (or 14.6 depending on design) until the current draw diminishes to near zero amps. This is fairly technical, which is why "smart' chargers are popular now days - you clip them on, walk away and they 100% charge your battery the shut off so as not to over charging it. The shutoff/startup feature means they're also brilliant for vehicles that don't get driven often - as someone mentioned earlier.

blakamin

4431 posts

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Inactive user

#1899280 11-Nov-2017 16:03

One of the management guys tried jumping my old 7 series once with a "portable power pack" (the CD changer was stopping the car going to sleep).

He bought it for his 4WD and this was the first time he used it.

It did nothing. Well, the dash lights came on... But that was it.

Might've if we left it for half an hour. Lucky he wasn't in the bush.

And it's not my battery that was the issue. It is only 2 years old... I swapped it into my X5 as I didn't know the age of that one, and it's still going strong.

geekIT

1943 posts

Uber Geek

#1899364 11-Nov-2017 20:10

tripper1000: This can get a bit technical, but essentially, your battery needs to sit at 14.4 volts (or 14.6 depending on design)...

Tripper, are you saying I should charge the battery until it shows 14.4\14.6 volts?

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elpenguino

2908 posts

Uber Geek

#1899371 11-Nov-2017 20:33

Excuse me for butting in but no, the charger(trickle or otherwise) puts out 14.4 v (Max) . You probably won't see more than 12. something from your battery.

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djtOtago

980 posts

Ultimate Geek

#1899399 11-Nov-2017 21:00

It is unlikely a trickle charger will over charge your battery. They just don't have the grunt to over charge.
I would trickle charge the battery for a least 24 hours.

RUKI

1346 posts

Uber Geek

#1899556 12-Nov-2017 11:52

Toyota Hybrid cars, e.g. Prius, Camry, Aqua, Lexus Hybrid use 7.2V NiMh modules in their High Voltage Battery Pack. Those packs use from 20 (Aqua) to 28, 34 or 40 models (some Lexus).

Those 7.2V (nominal) NiMH modules are about 1kg each, consist of 6 x 1.2V cells, and can withstand 100A discharge current. That is enough to start almost any light vehicle.

When those modules fail because of 1 cell out of 6 degrades more - entire module voltage drops below 7V. Those modules have enough "juce" to start your car. So you would need two in series (2kg pack), being compressed (mandatory) and safely connected to the car in the event of jump-start.

I am personally not doing that, but one of my mates told me he and his mate using that method.

Toyota / Lexus Hybrid and EV Battery Expert Battery Test & Repair

geekIT

1943 posts

Uber Geek

#1899636 12-Nov-2017 15:33

Thanks guys.

OK, I've just checked my recently charged battery and it was, indeed, sitting at around 11v.

This was the result of a 5-6 hour charge and a three km drive.

The charger, as predicted, is outputting just over 14v.

So I'll do a 24 hour charge. What battery voltage would you expect to see after that?

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Aredwood

3885 posts

Uber Geek

#1899643 12-Nov-2017 15:47

Around 12.8V with the battery charger disconnected. 11V with no load means that the battery is severely discharged.

Also have you verified that the cars charging system is working? Do you get 14+ volts on the battery terminals while the engine is running?

geekIT

1943 posts

Uber Geek

#1899654 12-Nov-2017 16:02

Engine running: 14.3v

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cadman

1014 posts

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Inactive user

#1899683 12-Nov-2017 17:33

allio:

I have a seldom-used car with a tiny battery that’s prone to going flat (Honda Jazz) so frequently have to deal with this.

Should just get a small, cheap charge-and-maintain charger and leave it connected to that battery when it's parked up. Lead-acid starting batteries don't like being slow discharged or kept at low voltages.

richms

26388 posts

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#1899692 12-Nov-2017 18:09

Also cheap transformer based chargers are at the mercy of line voltage to get enough output to actually charge things all the way, there is a 16% range of allowable voltage on the mains, a dumb transformer one will just pass that 16% fluctuation to the output. Put them on a low line voltage and they struggle to get up to 13v.

Richard rich.ms

RUKI

1346 posts

Uber Geek

#1899751 12-Nov-2017 19:32

richms:

Also cheap transformer based chargers are at the mercy of line voltage to get enough output to actually charge things all the way, there is a 16% range of allowable voltage on the mains, a dumb transformer one will just pass that 16% fluctuation to the output. Put them on a low line voltage and they struggle to get up to 13v.

Hint: Cisco Routers used in NZ Telco have PS inside which outputs 13.7V - perfect for Charging your LeadAcid battery :-)

Toyota / Lexus Hybrid and EV Battery Expert Battery Test & Repair

richms

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#1899763 12-Nov-2017 20:48

13.7 is a bit low tho, needs 14.4 to 14.6 to get them full. 13.7 will get it to cranking ok stage, but have stuff all reserve capacity in it. Takes days to weeks of typical driving to build that back up again on most cars.

Richard rich.ms

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