Can a jump starter charge a battery?

alchemysa · Mar 9, 2015

I Googled this question first but didnt find any useful answers. And I'm asking out of interest, not necessity. (I have 3 'real' battery chargers).

The pic below shows the set-up. The jump starter has a built-in 12v battery and its own built-in battery charger. So, why wouldn't the built-in charger also charge an external battery when its all connected and plugged into the mains power? I know it would probably be a very slow charge, but if time is no concern will it work?

One thing to note is that the internal 12v battery is sealed lead acid. Dunno if that matters.

Brad_Blazer · Mar 9, 2015

This manual says not to do it in the safety warnings:
h. Unplug the Power Pack from its Adapter
before connecting its cables to a battery.
http://manuals.harborfreight.com/manuals/38000-38999/38391.PDF

If the battery is completely dead it might be hard on the jump starter battery. Otherwise it seems like it would behave like a trickle charger once the 2 batteries are in equilibrium.

MoKelly · Mar 9, 2015

I have a Schumacher ProSeries 2200 unit and its manual warms against using the Starter as a trickle charger.

MoKelly

alchemysa · Mar 9, 2015

MoKelly said:
I have a Schumacher ProSeries 2200 unit and its manual warms against using the Starter as a trickle charger.

MoKelly

Most electric things you buy these days have more pages of warnings than actual instructions. Some are just plain stupid, others don't even apply to the product in the box.

Anyway, even if there is a genuine reason why it shouldnt be used as a charger my curious little mind would like to know what it is.

MoKelly · Mar 10, 2015

alchemysa said:
Most electric things you buy these days have more pages of warnings than actual instructions. Some are just plain stupid, others don't even apply to the product in the box.

Anyway, even if there is a genuine reason why it shouldnt be used as a charger my curious little mind would like to know what it is.

I don't know the technical reason --- if there even is a technical reason.

However, it seems to me if a starter would also function as a charger, the manufacturers would use that as a selling point. The fact they specifically say don't use the starter as a charger means something to me.

I have a wheeled unit that is BOTH a starter and a charger --- you just move the setting button.

Do you get the feeling I have way too many batteries to maintain and I fall a tad short in such maintenance?

MoKelly

mbohuntr · Mar 10, 2015

MoKelly said:
I don't know the technical reason --- if there even is a technical reason.

However, it seems to me if a starter would also function as a charger, the manufacturers would use that as a selling point. The fact they specifically say don't use the starter as a charger means something to me.

I have a wheeled unit that is BOTH a starter and a charger --- you just move the setting button.

Do you get the feeling I have way too many batteries to maintain and I fall a tad short in such maintenance?

MoKelly

Technical reason.... The batteries would not charge equally because they are not a matched set, the weaker battery would likely cook. The charge is controlled by voltage (pretty sure) on these type of batteries, and not by current or temperature.

SPYDERLK · Mar 10, 2015

alchemysa said:
Most electric things you buy these days have more pages of warnings than actual instructions. Some are just plain stupid, others don't even apply to the product in the box.

Anyway, even if there is a genuine reason why it shouldnt be used as a charger my curious little mind would like to know what it is.

Because not all jumpers use the same type of batt thats in the system youre jumping. Charge V may be slightly different and "could" cause trouble. ... Easiest for them to just say dont even tho 9 out of 10 would be ok.

mbohuntr · Mar 10, 2015

SPYDERLK said:
Because not all jumpers use the same type of batt thats in the system youre jumping. Charge V may be slightly different and "could" cause trouble. ... Easiest for them to just say dont even tho 9 out of 10 would be ok.

I didn't even consider different types of batteries than flooded lead acid.... Oh yeah, temp and current definitely apply!

alchemysa · Mar 10, 2015

SPYDERLK said:
Because not all jumpers use the same type of batt thats in the system youre jumping. Charge V may be slightly different and "could" cause trouble. ... Easiest for them to just say dont even tho 9 out of 10 would be ok.

So, temporarily disconnecting the internal battery might make it suitable as a slow charger?

A dedicated battery charger tends to be relatively heavy. I assume its because it contains a hefty heat sink. And also it contains the electronics to convert AD to DC.

Conversely the electronics in a jump starter are quite light. Is this because they are very slow chargers and dont require much of a heat sink? And they don't contain an internal AC/DC convertor.

SPYDERLK · Mar 10, 2015

Probably. Watch the assumptions tho. It may overcharge or undercharge depending on comparative V parameter of the batts. You should monitor the charge with a meter measuring batt V and not assume you can leave it for a long time unattended.