Wiring configuration for 2nd battery

[cat007]

Hey all

I'm wanting to make everything except starter and ignition run off the secondary 'house' battery.

The idea being, I can leave the stereo on, lights on, or anything on, and the main cranking/ignition battery wont drain down.

I've got a blocking diode. That part I've wired in. Now I'm just wanting a little advice as how to wire it up so the 'house' battery is effectively powering everything where-as the main battery sits doing nothing until I need to crank/start the engine.

Anywhere I should be looking or heading to?

[GTCRSHR]

isolator?

[cat007]

I've got a blocking/isolating diode in already. So the charge from the alternator feeds both batteries - but neither battery can steal charge from the other.

I guess what I'm asking is - is it a big job and does anyone know about the wiring in older hiace's, to wire up the ignition and starting circuits separately to the rest of the van's power circuits?

[Infinite]

just wire the sterio and your lights thru a new fuse box...
keep it simple

[Adydas]

i can check at work but there is a unit ideal for this design.. its used commonly on boats and i priced one to a customer all of 6 weeks ago..
$175 if i recall right but its a device that allows useable power on a boat via a 12v system but cuts off so there is sufficent power left in the batterys to restart the boat so you never get left with a flat battery.

Maybe this can help?

[matt dunn]

i can check at work but there is a unit ideal for this design.. its used commonly on boats and i priced one to a customer all of 6 weeks ago..
$175 if i recall right but its a device that allows useable power on a boat via a 12v system but cuts off so there is sufficent power left in the batterys to restart the boat so you never get left with a flat battery.

Maybe this can help?

A VSR or voltage switching relay,

much better than a blocking diode, but does the same thing.

His question is,

I have fitted that part, now what?

It's not that easy as all the systems are intergrated inot the same loom and power source,

but my suggestion would be, ( rather complicated though)

Find the main cable that goes to the starter motor,
run that to the starting battery and everything else to the house battery.
Fit a relay to the starting circuit,
power in from start battery, power out to starter,
relay coil in from the key or old start feed.
relay coil out to earth.

Needs the relay so that a flat house battery will have enough current to bring the starter in.

Not the best situation bay far,
petrol or diesil, as you may need to do similar with the coil/pump.

[cat007]

i can check at work but there is a unit ideal for this design.. its used commonly on boats and i priced one to a customer all of 6 weeks ago..
$175 if i recall right but its a device that allows useable power on a boat via a 12v system but cuts off so there is sufficent power left in the batterys to restart the boat so you never get left with a flat battery.

Maybe this can help?

Thanks for that - but the blocking diode I have will do a similar job to that - so I'd rather stick with it - and because I cant afford the $175 lol

thanks anyway

[cat007]

A VSR or voltage switching relay,

much better than a blocking diode, but does the same thing.

His question is,

I have fitted that part, now what?

It's not that easy as all the systems are intergrated inot the same loom and power source,

but my suggestion would be, ( rather complicated though)

Find the main cable that goes to the starter motor,
run that to the starting battery and everything else to the house battery.
Fit a relay to the starting circuit,
power in from start battery, power out to starter,
relay coil in from the key or old start feed.
relay coil out to earth.

Needs the relay so that a flat house battery will have enough current to bring the starter in.

Not the best situation bay far,
petrol or diesil, as you may need to do similar with the coil/pump.

That's exactly what I was after.

Currently the starter is wired directly to the main batt. I guess now I just need to wire everything to the house battery then single out and separate the coil, dizzy and starter circuits and wire them to the main battery....

That should be enough to get the engine running....?

[79rolla]

may also need fule pump and ecu if youv got them

[cat007]

may also need fule pump and ecu if youv got them

Nah its an old Hiace - no ECU and mechanical fuel pump I think....?

[cat007]

Ok so here's what I've done

After spending hours trying to figure out what plug does what and confusing myself over and over - I decided to run a new power wire straight to the back of the ignition switch. So basically everything else runs off the HOUSE battery while the starter motor and ignition switch runs off the MAIN battery.

Without this power wire, or with the ignition switch set to off - the headlights/internal lights still run and I'll re-wire the stereo so that it still runs as well.

Quite a mission to figure anything out without a wiring diagram lol

Will running a single wired to the ignition barrel do what I want? It appears to but I haven't fully tested it....

Peoples thoughts?

[cat007]

well it seemed to have worked

I left the head lights on all night, and interior light for good measure. in the morning the house battery was stone cold dead flat

turned key to ignition - dash lights up - so far so good - turn to start - engine cranks over mint and van starts as easy as ever

SWEET!

Now just got to wire the stereo to house battery so I can leave that running if need be

[t0ms]

be careful with the diodes.......

if you try and charge a flat battery like you just have your alternator could be poking anything from 30 - 80 amps into it through whatever sized diode. if its not big enough its going to get reall really hot and likely to cause so major damage....

VSR is prob the safest and cleanest way to achieve what you want.

[cat007]

be careful with the diodes.......

if you try and charge a flat battery like you just have your alternator could be poking anything from 30 - 80 amps into it through whatever sized diode. if its not big enough its going to get reall really hot and likely to cause so major damage....

VSR is prob the safest and cleanest way to achieve what you want.

The diode is rated to 130amp

Currently the crap stock alternator is only like 50 or 55 amp MAX - I'm putting in a 120amp holden one shortly

[sergei]

be careful with the diodes.......

if you try and charge a flat battery like you just have your alternator could be poking anything from 30 - 80 amps into it through whatever sized diode. if its not big enough its going to get reall really hot and likely to cause so major damage....

VSR is prob the safest and cleanest way to achieve what you want.

Not true about that high current.
Alternator does not know there is a second flat battery.
It will try to maintain ~14V and that is it. It does not have a charge out put, there is only one line. To get to 80A charging current the battery must have real low internal resistance, but the thing about Lead acid batteries is that they increase their internal resistance when discharged. (sulphuric acid is converted into lead sulphate, less ions = higher resistance).
So to get that current the battery must be stuffed (shorted).

[cat007]

Thanks for such an insightful response!

If a lead acid deep cycle bayterr is 105amp hour rated. Does that mean at 50amps it would take 2 hours to charge?

[sergei]

Thanks for such an insightful response!

If a lead acid deep cycle bayterr is 105amp hour rated. Does that mean at 50amps it would take 2 hours to charge?

Nope, there is charging efficiency as well, what would happen is that some current will be lost as heat.
What they mean is usually 5A load will last 21 hours (10A load will last less than half of time and so on, as higher the current less efficient the battery)

[matt dunn]

Thanks for such an insightful response!

If a lead acid deep cycle bayterr is 105amp hour rated. Does that mean at 50amps it would take 2 hours to charge?

Nope, there is charging efficiency as well, what would happen is that some current will be lost as heat.
What they mean is usually 5A load will last 21 hours (10A load will last less than half of time and so on, as higher the current less efficient the battery)

Be careful with amp hour ratings,

sure it may do 5A for 21 hours, but at the end of it it will be flat as in close to 0 volts, about 5hours into the 21hours it will be too flat to run a TV, start a car, do anything that requires kore than a few volts.

[Bling]

Why would you purposely drain a battery dead I mean I know you want to test your system out, but it can't be good for the battery to try and kill it.

Couldn't you have just disconnected the battery or something?

[MAGN1T]

A blocking doide isn't the cleverest of ideas because if it is in fact a diode there will always be .7 volt drop across it. That means that when the alternator voltage is say 14.2 max, the highest that the battery can charge to is 13.5 so will never fully charge (in reality it's probably a FET controlled by a diode but you won't know without tests or spec sheet).

The best way is either a manual switch, or if I was doing it, I'd build a voltage controlled relay to switch it in automatically when it's on charge, and to isolate it when off charge, with a manual reconnect for starting.

As mentioned before, my mate's camper van has a second battery on a manual switch, it's never let him down, nice, simple, cheap and effective.

There's also a minimum cell voltage that you should NEVER drop below.

Steve