ukclique > rec.cars.* > rec.cars.maintenance

Paddy Dzell (07.02.2019, 17:47)
I have a hybrid car and the 12V battery is under the boot floor, which
is awkward to get to if I ever need to jump start the car so I've
installed a socket in a more convenient and accessible place and I've
taken two wires directly from the battery to that socket.

The socket is keyed so there's no chance of any reverse polarity
accident occuring if I ever need to use my jump start battery pack but
I need to protect that cable run from any sort of accident resulting in
a short-circuit, so I bought a 12V circuit breaker rated at 30A (the
computers draw less than 20A to get the hybrid system to the 'READY'
state).

My question is - the circuit breaker has one connection labelled as
'Line' and the other one as 'Load', so is there anything in there that
means it will only operate with current flowing in that direction?

The wires from the battery to the socket will have a permanent 12V
supply on them. If I were to plug anything into that socket then
current would flow from battery to socket. However, it's purpose is to
do the reverse and provide 12V from an external source to the flat
battery so current flow would be from socket to battery, so will the
breaker work 'going one way' as an overcurrent device in case of a
fault but also allow current flow in the opposite direction when/if
needed?

Or should I just put a 30A in-line fuse in instead of the breaker?
Dave Plowman (News) (07.02.2019, 18:53)
In article <q3hjv2$7b3$1>,
Paddy Dzell <a> wrote:
> I have a hybrid car and the 12V battery is under the boot floor, which
> is awkward to get to if I ever need to jump start the car so I've
> installed a socket in a more convenient and accessible place and I've
> taken two wires directly from the battery to that socket.


> The socket is keyed so there's no chance of any reverse polarity
> accident occuring if I ever need to use my jump start battery pack but
> I need to protect that cable run from any sort of accident resulting in
> a short-circuit, so I bought a 12V circuit breaker rated at 30A (the
> computers draw less than 20A to get the hybrid system to the 'READY'
> state).


> My question is - the circuit breaker has one connection labelled as
> 'Line' and the other one as 'Load', so is there anything in there that
> means it will only operate with current flowing in that direction?


> The wires from the battery to the socket will have a permanent 12V
> supply on them. If I were to plug anything into that socket then
> current would flow from battery to socket. However, it's purpose is to
> do the reverse and provide 12V from an external source to the flat
> battery so current flow would be from socket to battery, so will the
> breaker work 'going one way' as an overcurrent device in case of a
> fault but also allow current flow in the opposite direction when/if
> needed?


> Or should I just put a 30A in-line fuse in instead of the breaker?


A diode will prevent reverse connection. 30 amp ones are not that
expensive. But will introduce about 0.6v voltage drop.
Paddy Dzell (07.02.2019, 19:12)
Dave Plowman (News) expressed precisely :
> In article <q3hjv2b3>,
> Paddy Dzell <a> wrote:
> A diode will prevent reverse connection. 30 amp ones are not that
> expensive. But will introduce about 0.6v voltage drop.


Thanks but I don't need a diode. The socket is keyed so that a reverse
connection can never happen. I need to know if the breaker will work as
an over-current device when the direction of current flow is from
battery to socket, but also allow current to flow in the opposite
direction if I need to use the jump start battery pack.

It's the fact that one leg of the breaker is 'Line' and the other leg
is 'Load' that's throwing me - is there something in the breaker that
needs it to be wired that way? A fuse would blow if there was
over-current in either direction but will a breaker allow current flow
both ways and still work as a breaker?
steve robinson (07.02.2019, 23:31)
On Thu, 07 Feb 2019 17:12:31 GMT, Paddy Dzell <a> wrote:

>Dave Plowman (News) expressed precisely :
>Thanks but I don't need a diode. The socket is keyed so that a reverse
>connection can never happen. I need to know if the breaker will work as
>an over-current device when the direction of current flow is from
>battery to socket, but also allow current to flow in the opposite
>direction if I need to use the jump start battery pack.


Unlikely its not designed to operate in that manner
>It's the fact that one leg of the breaker is 'Line' and the other leg
>is 'Load' that's throwing me - is there something in the breaker that
>needs it to be wired that way? A fuse would blow if there was
>over-current in either direction but will a breaker allow current flow
>both ways and still work as a breaker?


The line in is the power supply the load is the source of the power
requirement , its the load that's protected foam over voltage or over
current (depending on the type of breaker you are using) not the
supply . These can be protected electronically or electro
magnetically or a combination of the two , reversing the polarity of
the breaker may mean it will not work , or just trips out
D A Stocks (08.02.2019, 03:27)
"Paddy Dzell" <a> wrote in message news:7b31
>I have a hybrid car and the 12V battery is under the boot floor, which is
>awkward to get to if I ever need to jump start the car so I've installed a
>socket in a more convenient and accessible place and I've taken two wires
>directly from the battery to that socket.


Some hybrids have 12V jump start terminals as part of the inverter pack
under the bonnet. I think most Priuses have this.
Paddy Dzell (08.02.2019, 09:41)
D A Stocks submitted this idea :
> "Paddy Dzell" <a> wrote in message news:7b31
> Some hybrids have 12V jump start terminals as part of the inverter pack under
> the bonnet. I think most Priuses have this.


Yes, my car has one too. However, Sod's Law states that it'll be a
cold, wet, windy night when I need to get the engine bay covers off and
risk losing the little plastic clips while getting cold and wet. My new
socket is in the centre console cubby hole under the arm rest so that I
can do it all from the dryness of the drivers seat.
Theo (08.02.2019, 14:24)
Paddy Dzell <a> wrote:
> My question is - the circuit breaker has one connection labelled as
> 'Line' and the other one as 'Load', so is there anything in there that
> means it will only operate with current flowing in that direction?


What kind is the circuit breaker?
I assume it's suitable for DC, but is it thermal, magnetic, etc?

For example these thermal ones:

I would assume are bidirectional (it doesn't matter which direction the
current is flowing in, it'll still get hot)

but a magnetic one:

is assymetric according to the diagram, although exactly what that means is
unclear.

> The wires from the battery to the socket will have a permanent 12V
> supply on them. If I were to plug anything into that socket then
> current would flow from battery to socket. However, it's purpose is to
> do the reverse and provide 12V from an external source to the flat
> battery so current flow would be from socket to battery, so will the
> breaker work 'going one way' as an overcurrent device in case of a
> fault but also allow current flow in the opposite direction when/if
> needed?


In those designs, it looks like current will flow both ways unless tripped.

You could test it by applying a >30A load to find out.

Theo
(pondering whether the lead acid battery could be replaced entirely by one
of those jumpstart packs)
Paddy Dzell (08.02.2019, 14:36)
Theo presented the following explanation :
[..]
> Theo
> (pondering whether the lead acid battery could be replaced entirely by one
> of those jumpstart packs)


Thanks Theo. It's one of these but I don't know if it's thermal or not:

Brian Reay (08.02.2019, 16:24)
On 07/02/19 15:47, Paddy Dzell wrote:
[..]
> 'going one way' as an overcurrent device in case of a fault but also
> allow current flow in the opposite direction when/if needed?
> Or should I just put a 30A in-line fuse in instead of the breaker?


It rather depends on how the breaker works. If it is electronic, it may
only function correctly if inserted in circuit as labelled,

I'm a bit surprised there isn't a 'jump start' terminal already provide.
My Hybrid Outlander also has its 12V aux battery in the boot and, like
yours, isn't easy to access. (There is a removable cover to allow you to
disconnect the -ve/earth but the +ve side is tucked away.) However,
under the bonnet, there is a special terminal provided to allow you to
connect a 12V external battery to jump start the vehicle. Like yours,
it only really jump starts the electronics, not the engine, the starter
motor is powered from the main drive battery under the floor on the
Outlander. I've read of people using small (in terms of capacity)
batteries to jump start Outlanders as only a relatively small current is
required (I'm not sure what but I suspect far less that 20A.)

As for a fuse vs breaker, given it will only be used 'once in a blue
moon' (hopefully) I'd opt for a fuse and carry a spare, just in case.
Brian Reay (08.02.2019, 16:40)
On 08/02/19 07:41, Paddy Dzell wrote:
> D A Stocks submitted this idea :
> Yes, my car has one too. However, Sod's Law states that it'll be a cold,
> wet, windy night when I need to get the engine bay covers off and risk
> losing the little plastic clips while getting cold and wet. My new
> socket is in the centre console cubby hole under the arm rest so that I
> can do it all from the dryness of the drivers seat.


Ah, that makes more sense now- I would have been surprised if a jump
start point wasn't provided. I wonder, does your hybrid not charge the
aux battery when the vehicle is parked for an extended period from the
main (drive) batteries? The Outlander does this (I think at 2pm, why
2pm I don't know) if the vehicle hasn't been driven for (I think 24
hrs). I've left our Outlander, main (drive)battery charged but not quite
fully for 5 / 6 weeks and it started first time, with no noticeable drop
in drive battery charge (ie range). I don't leave in hooked up when we
are on holiday etc. Whether it will do the same when the batteries are
older time will tell- it is only just over a year old.
Paddy Dzell (09.02.2019, 01:09)
Brian Reay wrote :
> On 07/02/19 15:47, Paddy Dzell wrote:
> It rather depends on how the breaker works. If it is electronic, it may only
> function correctly if inserted in circuit as labelled,
> I'm a bit surprised there isn't a 'jump start' terminal already provide. My
> Hybrid Outlander also has its 12V aux battery in the boot and, like yours,
> isn't easy to access. (There is a removable cover to allow you to disconnect
> the -ve/earth but the +ve side is tucked away.) However, under the bonnet,
> there is a special terminal provided to allow you to connect a 12V external
> battery to jump start the vehicle.


Yes, my car has one too. However, Sod's Law states that it'll be a
cold, wet, windy night when I need to get the engine bay covers off and
risk losing the little plastic clips while getting cold and wet. My new
socket is in the centre console cubby hole under the arm rest so that I
can do it all from the dryness of the drivers seat.

> I've read of people using
> small (in terms of capacity) batteries to jump start Outlanders as only a
> relatively small current is required (I'm not sure what but I suspect far
> less that 20A.)


15.32A for my Lexus RX450h to reach the 'READY' state.

> As for a fuse vs breaker, given it will only be used 'once in a blue moon'
> (hopefully) I'd opt for a fuse and carry a spare, just in case.


Cheers, think I will.
Brian Reay (09.02.2019, 10:45)
On 08/02/2019 23:09, Paddy Dzell wrote:
> Brian Reay wrote :
>> I've read of people using small (in terms of capacity) batteries to
>> jump start Outlanders as only a relatively small current is required
>> (I'm not sure what but I suspect far less that 20A.)

> 15.32A for my Lexus RX450h to reach the 'READY' state.


I'm surprised it is as high as that but I assume you've checked /
measured it so accept what you say.

I'm curious what it is all powering- 15A at 12V is 180W- a couple of
laptops worth.
Paddy Dzell (09.02.2019, 12:02)
Brian Reay presented the following explanation :
> On 08/02/2019 23:09, Paddy Dzell wrote:
> I'm surprised it is as high as that but I assume you've checked / measured
> it so accept what you say.


Yep, here's a photo:

Brian Reay (09.02.2019, 13:22)
On 09/02/19 10:02, Paddy Dzell wrote:
> Brian Reay presented the following explanation :
> Yep, here's a photo:
>


I wasn't doubting you but thanks for the photo.

I'm still curious what is is being used for. A decent laptop (in terms
of performance) would have perhaps a 60 or at most 90W PSU so we are
looking at between 2 and 3 times that. But a laptop has all the
graphics, a car only has one set, and graphics can be needy in terms of
power. (I'm still not disputing your 15A, just trying to play with the
numbers- I'm a cross between an Engineer and a Mathematician, 25 years
as one and 11 year teaching Maths, degrees in both, makes you rather a
tinker with such things ;-)

I like you idea of a jump start point accessible 'in the warm'. I'm
planning to add some wiring to the 12V battery in my Outlander to power
some amateur radio kit and, while I have the boot floor up etc, I may
run an extra cable, just in case.

We used to have a CRV and, when it was left parked during our long
(motorhome) jaunts, the battery often ran flat. In the end, I ran a
cable to the rear so I could link it to a float charger- all protected
with diodes and fuses in case we forgot and tried to drive it away or
someone tinkered with it one the drive (at the time, we had another car
in the garage).
Paddy Dzell (09.02.2019, 14:07)
Brian Reay wrote :
[..]
> the rear so I could link it to a float charger- all protected with diodes and
> fuses in case we forgot and tried to drive it away or someone tinkered with
> it one the drive (at the time, we had another car in the garage).


No worries my friend, I know you weren't doubting me but yes I agree,
15A does seem a lot just to power up a couple of ECUs.

Good idea on running a spare cable just in case - from John G7IFM :')

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