Mini jump starter as a regular engine start battery?

V

Venus1

Well-Known Member
Joined
2 Aug 2014
Messages
151
Visit site
It's feasible to have a red flash or similar dedicated engine start battery (and some deep cycle house batteries).
There must be a reason why a less expensive "mini jump starter" couldn't be used in the same way - ie permanently wired in as the engine start battery.
Is the reason that, with only approximately 1ampHr, it would not be able to grind for long if there was trouble starting?
 
Yes. Able to push the high amperage for just a few seconds. A cranking battery can sustain the several hundred amps needed for a 4 cyl engine usually for several minutes. Might be an application for a mini jump battery for lightweight engines such as an es outboard that doesnt take a heavy current? The thankfully obsolete Dynastart only took around 30 -50 amps to start a Stuart or Vire.
 
Venus1 said:
It's feasible to have a red flash or similar dedicated engine start battery (and some deep cycle house batteries).
There must be a reason why a less expensive "mini jump starter" couldn't be used in the same way - ie permanently wired in as the engine start battery.
Is the reason that, with only approximately 1ampHr, it would not be able to grind for long if there was trouble starting?
Click to expand...

rather than one of the "mini jump starters", which often come with lights and tyre inflation compressors rolled into the same package, you could look at replacement AGM batteries for them.

You should be able to find ones with a reasonable Ah capacity 18Ah for example.
 
Last edited:
Small batteries can start big engines.
The little 12V battery in my motorbike has a CCA rating of 215Amps.
However, I suspect that these batteries will have a short life in terms of number of starts. They often don't last many years, but that's partly neglect.
Jump packs are normally only expected to be used very occasionally.
I don't think the starter battery is a good target for scrimping.
 
oldharry said:
No. A 1kw starter for a small car of say 1.0l engine may only take 80 - 90 amps, but to start say a 2.5l diesel can take 3-4 times that to get it turning fast enough to fire.
Click to expand...

also I think you will find that the kW rating of a starter motor is the mechanical output power. The electrical consumption is even higher!
 
V1, what is it you are trying to do? We have just replaced the Redflash start battery with a standard AGM car battery due to the outrageous cost of Redflash batteries. The only difference is the Varta battery doesn't cause the starter motor to slow down after 10 seconds of cranking which the Redflash did.

Pete
 
oldharry said:
No. A 1kw starter for a small car of say 1.0l engine may only take 80 - 90 amps, but to start say a 2.5l diesel can take 3-4 times that to get it turning fast enough to fire.
Click to expand...

About right. A 2.4l Transit will be fitted with one or two 590a batteries, the starter will typically draw 250-300a.
 
The inrush current when the starter is initially not moving is very high.
Limited only by the resistances of the battery, wiring and motor.
Too small or weak a battery will make this current smaller, but can make it last a lot longer.
A good way to ruin a starter is to power it from a nearly flat battery where it remains stalled but still draws a lot of amps.
Once the motor is turning, it generates a back emf, which reduces the current.
The nominal electrical power of the motor will be with it spinning at some nominal rpm, perhaps 400rpm of the engine. But it may be stated at the voltage expected from a 'normal size' 12V battery, like perhaps 9 or 10V?
Too big a battery might up the running current by exceeding the cranking voltage expected, but this will usually result in the engine starting more quickly.

Maybe the max battery size is on the assumption that somebody will keep cranking a sick engine until the battery is flat?
Personally, I don't think the start battery is a good thing to minimise. Even if it works OK at first, how long will it last?
A 200kg motorbike is a good place not to be carrying a bigger battery than the absolute minimum. A reasonable size yacht, not really.

Small car batteries offer a lot of CCA per £, maybe paralleling two if that fits in available space?
Another point, the actual CCA spec can be quite different from one manufacture to another, for the same 'model' of battery. For one of my bikes, the Yuasa is 20% better than the 'equivalent' Exide.
Also, there are at least two CCA rating tests, EN and SAE IIRC so be careful to compare like with like.
 
Here is a curve or 3 for a notionally 2.9kW starter:
http://www.newindo.com/delcoremy/images/28MT-12V_pc.jpg
That's for up to 6 litres or something.
Our engines will mostly have smaller, but until the engine is up to speed, the current is 'lots'!
It shows the motor is designed around the voltage falling to around 8V at peak power.

The graphs for the starter on my bike are similar but a fraction of the current.
 
Venus1 said:
It's feasible to have a red flash or similar dedicated engine start battery (and some deep cycle house batteries).
There must be a reason why a less expensive "mini jump starter" couldn't be used in the same way - ie permanently wired in as the engine start battery.
Is the reason that, with only approximately 1ampHr, it would not be able to grind for long if there was trouble starting?
Click to expand...

Machine Mart do a 38 Ah jump start (think it's called 4000) does a good job.
 
Pete7 said:
V1, what is it you are trying to do? We have just replaced the Redflash start battery with a standard AGM car battery due to the outrageous cost of Redflash batteries. The only difference is the Varta battery doesn't cause the starter motor to slow down after 10 seconds of cranking which the Redflash did.

Pete
Click to expand...
That is a fair question!
I guess, as well as being generally curious, I would like a red flash substitute for less cost. I have taken all posts as interesting and helpful.
 
You must log in or register to reply here.

Share this page

Top