Is leaving a circuit breaker open bad?

yorke7

New Member
So i'm not auto electrician but like many others i wanted a 2nd battery, 12v setup but couldn't afford an auto electricians services. I learnt, consulted a 12v expert and eventually built one myself. It's been in and working for over a year now with no problems at all, but with the cold weather lately i've noticed my ute taking a long time to start. Eventually it wouldn't start at all and i found it weird because i had just driven about 30 mins, turned off the car, went to start it again not 5 min later and it wouldn't at all, as if the starter were 100% dead. I got the jumper cables out but thought i'd try something first.

I have a circuit breaker in the engine bay between the starter and the 2nd battery in the canopy, this circuit breaker can be deliberately triggered by pressing a button, thus disconnecting the starter from everything else. But this shouldn't make any difference as I have a projecta 25A DC-DC, which should stop the 2nd battery from taking any power away from the starter? Anyway I open the circuit breaker, try starting the car again and it starts first try, straight away, easy as you please. I have no idea why this happened and have since closed the circuit breaker again but have noticed the car taking longer and longer to crank over...again.

So my question is two fold: does anyone know what is going on here? and if not is there a problem with just leaving the circuit breaker open when i'm not drawing any power from the 2nd battery? I rarely get to camp these days and when not camping nothing is drawn from the secondary battery, so i'm thinking about just leaving the breaker open until i go on a trip again and need charge for the 2nd battery. But i don't know if leaving it open is bad? or if deliberately tripping and reseting the breaker over and over is also bad?

Apologies for the small essay, I tried to only write whats needed to know for this specific problem aaand in light of that; yes i do have circuit breakers that are closer to the secondary battery and on everything, not just the one in the engine bay.

Thanks for your time to anyone who read this,
Yorke
 

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Triton14

Well-Known Member
But this shouldn't make any difference as I have a projecta 25A DC-DC, which should stop the 2nd battery from taking any power away from the starter? Anyway I open the circuit breaker, try starting the car again and it starts first try, straight away, easy as you please. I have no idea why this happened and have since closed the circuit breaker again but have noticed the car taking longer and longer to crank over...again.

So my question is two fold: does anyone know what is going on here? . But i don't know if leaving it open is bad?
Sounds to me like your starter is the problem, not holding charge.
Do you have a multi meter to check it?
Or a charger with a desulphite setting??

If you have a DC-DC charger as you state it should disconnect from the aux once the starter gets to something like 12.9V (or whatever yours states).
So leaving the breaker open would have no affect anyway when sitting.
 

cookie64

4x4 Earth Contributer
Do I read this right? You are shorting out the Starter Battery after the circuit breaker in order to make the breaker trip between the starter battery and the Projecta DC-DC? If so, don't, you are risking heavy currents flowing through to the switch and wiring and potentially a fire when the insulation breaks down, you may also be prematurely stuffing your starter battery. You really don't need to isolate the Projecta as that will in itself isolate from the Starter Battery when the 4wd is not running.

Hope this helps

cheers
 

Albynsw

Well-Known Member
So you are saying the car won’t start when the batteries are linked but will start when they are isolated ?
If that is the case your second battery is the problem and sucking the power out of your crank battery
 

Chatty

Well-Known Member
Ok, so, your Projecta Dc-DC charger may be set to turn off when the cranking battery falls below 11.9V (that's in 'Smart Alternator' mode) which would be way too low for adequate cranking of the engine. For 'Conventional Alternator' mode it is 12.8V, which should be ok.

Looking at what you've said, I suspect your cranking battery is reaching the end of its life, and is marginal on achieving adequate cranking voltage and current - the 30A (ish) (25A + charger losses) that the DC-DC charger is drawing may be just enough to tip it over the edge into no-go on cranking.
My advice would be get your cranking battery tested before you go much further.

To answer your question - you can leave the circuit breaker open without any issues, apart from the fact that your aux battery will now not be receiving any charge. That means in a couple of months or so, the aux battery will self-discharge to the point where it is permanently damaged. To prevent this, you would need to close the circuit breaker for an hour or so every 3 or 4 weeks, to ensure the aux battery is kept charged.
 

sharkcaver

Well-Known Member
the 2 things you need to check

1. Start battery performance load test
2. current draw through that breaker to confirm when closed no excessive parasitic current is being drawn (short/faulty idc25/faulty 2nd battery)

Personally, I'd be leaning towards an IDC set up to smart alternator mode (meaning 11.9V cut off voltage) coupled with an under performing start battery.

If it's set up to smart alternator mode, you could disconnect that IGN source wiring on the IDC, meaning cut off voltage is now 12.8V and see what effect that has on your start battery.
 

yorke7

New Member
Thanks for the advice everyone, I won't open the circuit again to be safe and I'll go get the starter checked first off because this was initially what i thought the problem was too, i just found how isolating the starter and aux got the car started weird. If the starters all good then i'll take a look at the aux battery, though i don't think it's dropped a cell because it still reads full charge after a drive.
 

yorke7

New Member
Ok, so, your Projecta Dc-DC charger may be set to turn off when the cranking battery falls below 11.9V (that's in 'Smart Alternator' mode) which would be way too low for adequate cranking of the engine. For 'Conventional Alternator' mode it is 12.8V, which should be ok.

Looking at what you've said, I suspect your cranking battery is reaching the end of its life, and is marginal on achieving adequate cranking voltage and current - the 30A (ish) (25A + charger losses) that the DC-DC charger is drawing may be just enough to tip it over the edge into no-go on cranking.
My advice would be get your cranking battery tested before you go much further.

To answer your question - you can leave the circuit breaker open without any issues, apart from the fact that your aux battery will now not be receiving any charge. That means in a couple of months or so, the aux battery will self-discharge to the point where it is permanently damaged. To prevent this, you would need to close the circuit breaker for an hour or so every 3 or 4 weeks, to ensure the aux battery is kept charged.
Makes sense, cheers for this i appreciate it.
 

yorke7

New Member
Do I read this right? You are shorting out the Starter Battery after the circuit breaker in order to make the breaker trip between the starter battery and the Projecta DC-DC? If so, don't, you are risking heavy currents flowing through to the switch and wiring and potentially a fire when the insulation breaks down, you may also be prematurely stuffing your starter battery. You really don't need to isolate the Projecta as that will in itself isolate from the Starter Battery when the 4wd is not running.

Hope this helps

cheers
Not shorting anything out, just manually opening the circuit breaker myself by pressing the button, I would never deliberately short the system just to cause the circuit breaker to open if thats what you mean? And yeah i know i shouldn't need to isolate the starter from the aux battery since i have the dcdc but then why did breaking the connection allow my car to start when it seemed dead?

Anyway thanks for the help man
 

LockyerLad

New Member
I'd also be doing a close check on the earthing straps for both batteries and the starter motor. Is the aux battery connected directly to the engine or just to a convenient point on the chassis?
 

Triton14

Well-Known Member
I'd also be doing a close check on the earthing straps for both batteries and the starter motor. Is the aux battery connected directly to the engine or just to a convenient point on the chassis?
Yes on reflection I guess the very 1st thing to do is check all the cable & terminal connections.

It's easy for a solder/crimp to become lose over time.

But the cold of winter is usually when a battery will show any signs of weakness.
So my other question would be how old I'd the starter, that wasn't mentioned?
 

yorke7

New Member
I'd also be doing a close check on the earthing straps for both batteries and the starter motor. Is the aux battery connected directly to the engine or just to a convenient point on the chassis?
The aux battery is earthed back to the starter battery, which i'm unsure where that's earthed but it hasn't been touched from factory so the chassis i'm guessing? something i'll check tomorrow, thanks for the help.
 

yorke7

New Member
Went to supercheap and got the starter battery tested today, their device wouldn't work and they weren't able to tell me whether thats because it just doesn't work sometimes or because something is drawing from the starter. Nothing was drawing from the aux battery and thats all that's connected to the starter so i'm not sure what it could be. I checked all the fuses, circuit breakers, cabling and terminals that i can easily access (probably about 80%) and they were all fine. Supercheap staff just told me to see an auto elec but im going to visit a car battery specific place and see if they have more knowledge first.

Appreciate all the replies, thanks legends
 
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a1bert

Active Member
yorke7 as mentioned previously, looks like you drive a Ford Ranger, my Ranger is earthed back to the chassis near the battery, not to the battery, this is a no no on my model and sure it would be on yours!
Best read your book
 

yorke7

New Member
yorke7 as mentioned previously, looks like you drive a Ford Ranger, my Ranger is earthed back to the chassis near the battery, not to the battery, this is a no no on my model and sure it would be on yours!
Best read your book
So you mean to say that the starter on rangers arn't earthed?
 

Chatty

Well-Known Member
The aux battery is earthed back to the starter battery, which i'm unsure where that's earthed but it hasn't been touched from factory so the chassis i'm guessing? something i'll check tomorrow, thanks for the help.
It looks like you're in a Ranger - I remember one of the members saying that on a Ranger you shouldn't connect the aux battery earth to the cranking battery earth - apparently the aux battery earth should be to the chassis at the cranking battery earth point or close to it.

I don't have a Ranger, so I can't comment in any knowledgeable way, but it stuck in my mind - maybe ask the question on one of the Ranger pages888*-
 

TimNWVic

Active Member
The later model Rangers have a current shunt on the battery negative. All negative connections must be on the chassis side of this, including the main vehicle chassis earth. This is so the so called smart alternator can adjust it's output according to load.

If you put a large load (eg 2nd battery charging) on the wrong side of the shunt, the vehicle computer won't adjust the alternator output to compensate, so it will run the start battery down. They only charge the start battery to about 85% anyway, by design.

I have a 2020 Ranger, 140aH AGM battery and Redarc BCDC in the tray, earthed to chassis behind the cab. Never had a problem in this vehicle or the identical setup in my previous BT50 (non-smart alternator in the older Mazda).
 
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yorke7

New Member
Okay cheers guys i'll check this out, sounds like i stuffed up by just earthing it back to the negative terminal on the starter.
 
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