Charging a jump starter

Submitted: Tuesday, Feb 09, 2010 at 11:37
ThreadID: 75897 Views:10773 Replies:3 FollowUps:2
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Hi folks
I have a Projecta battery pack/jump starter. I've had it for a few years and have found it very handy when camping and 4wd'ing. I use it to power the 12 volt light in the tent, the portable compressor and various other uses. The tiny 240 and 12 volt chargers supplied with it gave up the ghost some time ago. Since then I have been charging it with a 4amp projecta charger(240 obviously). I simply connect the alligator clips on the charger to the corresponding alligator clips on the battery pack. This is a bit of hit and miss and I usually just give it about 12 hours, take it off, leave it for a while and the check the voltage on a meter. If it's somewhere around 13.4 that will do. Not great I know - but it works for me.
My problem is this. We are going on an extended offroad trip this year and I expect that the more frequent use involved will probably mean that the pack needs recharging at some stage before we get back to civilisation. I am running a vehicle with one of Derek's Flyer setup's as a second battery(120ahAGM). Can I just connect the alligator clips on the battery pack to the corresponding poles on the Flyer and effectively make the pack a third battery in line and charge it up that way. It seems a much more appropriate way of charging than running my charger through the inverter and then connecting the pack to that.

thanks in anticipation

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Reply By: Mandrake's Solar Power- Tuesday, Feb 09, 2010 at 12:30

Tuesday, Feb 09, 2010 at 12:30
Might be best to send a MM to Derek direct or email him ..


AnswerID: 403412

Reply By: Member - Oldbaz. NSW. - Tuesday, Feb 09, 2010 at 16:26

Tuesday, Feb 09, 2010 at 16:26
I too carry one when camping, great for lights ,shower pump etc & independant
of vehicle. I leave it connected in the back of the wagon when travelling via the
12 volt charging cord. I'm sure you could buy a replacement cheaply from Dick
Smith or Autocrap for either 12v or 240....oldbaz.
AnswerID: 403441

Follow Up By: Member - Oldbaz. NSW. - Tuesday, Feb 09, 2010 at 16:53

Tuesday, Feb 09, 2010 at 16:53
teege, just checked my chargers, both have a hollow round pin,about 2mm at
one end. 12v is just a cig plug,240 is a 3pin block AC/DC , output is 500ma. My
rechargeable flouro lantern uses same setup. If yours has a small centre pin
in charging socket to accept round pin, you should be able to obtain easily.
FollowupID: 672906

Follow Up By: Member - Teege (NSW) - Tuesday, Feb 09, 2010 at 17:59

Tuesday, Feb 09, 2010 at 17:59
Thanks Baz
I'll see how I go. Still interested to see if my idea is a goer or not.

FollowupID: 672923

Reply By: AdrianLR (VIC) - Wednesday, Feb 10, 2010 at 22:32

Wednesday, Feb 10, 2010 at 22:32
A couple of thoughts....

The jump starter has a SLA battery which doesn't like a charge rate of greater than 10% in amps of the amp hour rating. Depending on the size of the jump starter it will probably have a 7Ah or 18Ah battery so 0.7A or 1.8A as a maximum charge rate. The cigarette lighter adapter, with thin wiring to the socket and from the adapter to the jump starter restricts the current and, just as you're suggesting, parallels the jump starter with the main battery. Each battery then draws whatever current it can/needs relatively safely.

However (I hear you say), that's not quite what you're doing. By putting the leads from the jump starter with a flat battery directly onto the alternator even though there are another two batteries in parallel could send a very high current to the SLA and kill it pretty quickly.

Another issue is that without the engine on, the SLA wont be charging. At least this is the way the jump pack I've got reacts. The AC plugpack in my case is rated at 15V and puts out about 17V and around 14V under load. That's enough (i.e. greater than 13.8V) to charge the SLA. Plugging in the cigarette adapter doesn't charge the battery at all. In fact in my old Discovery (but not the Pajero) the jump pack would energise the Acc circuit and draw lots of charge OUT.

So.....whilst driving use the cigarette adapter and when stopped you could use something like a small 12V laptop power supply that has a rating of 1.5A set to 13.8V although these may be hard to find as the ratings now all seem to be 2.5A or greater. An alternative is to build a 12V converter kit that Silicon Chip magazine ran a few years back that could deliver 13.8V at about 1.5A.

I think my logic is ok but would be interested in another view if someone has actually tried your much simpler setup.


AnswerID: 403696

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