dual batteries clarified :)

[Shadow]

hey, gonna put a dual battery setup in the 60, only real reason is i have a spare battery and the 60 pulls a lot of juice to start.

I want the 2nd battery to help the starter motor fire

I have searched and read the wealth of knowledge in this forum, just like to clarify the system i intend to use before i pay out the $$$ for solenoids and cables.



See the attached image, this is what i intend to impliment.

Now the wiper motor gets power as soon as the "ON" position is selected, ie glow plugs firing, starter motor ready to fire.

this means that i will have the CCA of the two batteries for the starter motor correct?

Will this stress my altenator ? charging two batteries? in theory the dual batteries could pull twice as much current from the altenator, and maybe burn it out?

the altenator brushes and diodes were done about 2 years ago.


Lastly, what solenoid should i buy, just goto auto elec and say want a solenoid for dual batteries? or ask for specific brand/type?

Thanks guys.

I know this has all been said, and i have read it, but there are alot of conflicting views. Just want to make sure what i think i now know is correct

[chimpboy]

If you are purely doing this for more grunt at start-up, and you're not trying to set up a system where you can run a fridge etc off an auxiliary battery overnight and so forth, you don't need to fuck around with solenoids or anything, just hook the two batteries together and that's that.

On the other hand if you do want to isolate one battery when the engine's not running, I think the best option is one of these or the same kinda thing from Dick Smith.

It's a bit more intelligent than the solenoid set up and not very expensive.

You don't need to worry about stressing the alternator to charge both batteries. It should make no difference.

Jason

[Shadow]

If you are purely doing this for more grunt at start-up, and you're not trying to set up a system where you can run a fridge etc off an auxiliary battery overnight and so forth, you don't need to ***** around with solenoids or anything, just hook the two batteries together and that's that.

On the other hand if you do want to isolate one battery when the engine's not running, I think the best option is one of these or the same kinda thing from Dick Smith.

It's a bit more intelligent than the solenoid set up and not very expensive.

You don't need to worry about stressing the alternator to charge both batteries. It should make no difference.

Jason

what extra does it do.

im a micro electronic engineering student and could make pretty much anything.

i have thaught about timers ammeters and voltmeters etc for charging, but that would kill the extra starting ability of the dual batteries.

[landy_man]

if all you are doing this for is starting then i suggest you check your starting battery or get a higher CCA rated unit...
the system you describe above is a very basic setup bt does allow you to disconnect the second battery for any reason.

[Slayer]

i think you will find that hooking them up pos to pos with a manual isolator will be best for you, acts the same as the switch u used in the illostration and saves u the $$ and the extra cable.. leave them conected all the time, or leave one isolated for ermergincies..
thing as far as i under stand when hooking batteries in paralell.. ie posive to positve, ground to ground when u join two batteries with say 500 cold cranking amps (cca) this doesnt give you 500 + 500, or 1000.. it gives you 500, but in theary it should be avalible for 2 times as long..

if you want more Boot when u crank it over 2 batteries wont provide this any better than one will.. its all about the cca rating.. you would get better cranking from a single battery rated at 900cca than you would from 2 700's.. sure the singhle battery will go flat quicker if ur continuously cranking and the motor doesnt start.. but you said you wanted more omph.. look into the bigger battery and stay singlular till u need it for auxileries maybe??

just an opinion, somting to ponder ymmv

cheers

[ORSM45]

the alternator is only going to give out as much as its load is drawing.

dont get voltage and current mixed up here.

in a parallel setup (which is what you want for a 12v system using 2x 12V batteries) when charging, the voltage is the same across both batteries but the current is half to each. (note. you have 2 of the same size/brand batteries) so if you have a 80amp alternator, it will now be 40amps to both batteries. but only when its needed.

MaccA

[bazzle]

Just get a good starting battery and ensure all terminals clean and alt set correctly.
Increase size of battery leads, ie earth and lead to starter motor.
You shouldnt need 2 batt just for starting.

Bazzle

[-Scott-]

if you want more Boot when u crank it over 2 batteries wont provide this any better than one will

WTF?

... its all about the cca rating..

Yes

you would get better cranking from a single battery rated at 900cca than you would from 2 700's..

Don't know about that, but I tend to doubt it.

Two 600CCA batteries in parallel WILL give better starting performance than a single 600CCA battery. Each battery will be supplying less current, so each will have a higher terminal voltage, so the starter motor WILL have more power. You would need to look at internal resistance figures or current/voltage curves to work out how large a single battery would need to be to outperform two 600CCAs in parallel.

If you take a signal from the wiper motor for the solenoid, check that the wipers still work while the engine is cranking - in some cars the accessories are turned off during starting, so the solenoid may be off when you actually want it on.

Jaycar (among others) supply an isolation kit using two 50A FETs in parallel to provide the isolation. When the engine starts the circuit waits for the starting battery to recharge before it starts charging the second battery, and even has a low charge rate to avoid cooking a severely discharged Deep Cycle battery (which normally don't like large charge currents.) Although this circuit will stop the auxiliary battery draining the starting battery, the FETs operate like large diodes in the opposite direction. This allows the auxiliary battery to provide some assistance during starting, but not as good as a hardwire between the two.

The only thing this circuit lacks is a low voltage cut-out option for auxiliary battery - no big deal, but it means I've gotta build one sometime...

Cheers,

Scott

Edit: The Jaycar kit I mentioned is the same one Chimpboy linked too - missed the link first time through...

[murcod]

I wouldn't rely on the Jaycar / Dick Smith kit for extra starting current..... I know it's got the diodes within the FET's, but straight away you've lost 1.2v at least (voltage drop across the forward biased diodes). Plus the kit requires a fair amount of resisitance in the aux battery line for the circuit to function- so, basically there's going to be so much voltage dropped it will be next to useless for assistance.

[Leprecaun]

I wouldn't rely on the Jaycar / Dick Smith kit for extra starting current..... I know it's got the diodes within the FET's, but straight away you've lost 1.2v at least (voltage drop across the forward biased diodes). Plus the kit requires a fair amount of resisitance in the aux battery line for the circuit to function- so, basically there's going to be so much voltage dropped it will be next to useless for assistance.

Will this still work in charging that second battery. I have my main which is a 790 cca and a smaller 450cca that I want to use as a second battery to power fridge and compressor in the back. The main battery starts the bi$ch up first kick but will the second lower rated amp charge up off the main battery then If thats right then $50 bucks for a isolator kit far cheaper than some of the smart solenoid setups you see . As when the car is off you just throw the switch and isolate battery and use that instead.

[chimpboy]

I wouldn't rely on the Jaycar / Dick Smith kit for extra starting current..... I know it's got the diodes within the FET's, but straight away you've lost 1.2v at least (voltage drop across the forward biased diodes). Plus the kit requires a fair amount of resisitance in the aux battery line for the circuit to function- so, basically there's going to be so much voltage dropped it will be next to useless for assistance.

Will this still work in charging that second battery. I have my main which is a 790 cca and a smaller 450cca that I want to use as a second battery to power fridge and compressor in the back. The main battery starts the bi$ch up first kick but will the second lower rated amp charge up off the main battery then If thats right then $50 bucks for a isolator kit far cheaper than some of the smart solenoid setups you see . As when the car is off you just throw the switch and isolate battery and use that instead.

Yes, that is pretty much the intended purpose of the $50 units.

Jason

[Leprecaun]

Geez I'm glad I never forked out for the solenoid systems, thanks for the confirmation chimpboy.

[Rainbow Warrior]

If you're jus using it for starting just connect 2 batteries in parallel all the time, forget any solenoids.

Just make sure both batteries are the same in type and age so one is not overcharging, in other words buy 2 brand new ones together.
Alternatively just fit a bigger battery instead, a single battery is fine for starting over 99% of 60 Series out there why does yours need 100% more?
Do you have bodgy starter motor or connections perhaps? Is it going half flat overnight due to something draining it?

[chimpboy]

Just make sure both batteries are the same in type and age so one is not overcharging, in other words buy 2 brand new ones together.

This is only really an issue when connecting two batteries in series for a 24V system - in that setting, having near-identical batteries is critical.

When connecting in parallel, you should be okay as long as neither battery is actually stuffed. If they are both in good condition you can hook them up in parallel without any hassles.

Jason

[Rainbow Warrior]

Just make sure both batteries are the same in type and age so one is not overcharging, in other words buy 2 brand new ones together.

This is only really an issue when connecting two batteries in series for a 24V system - in that setting, having near-identical batteries is critical.

When connecting in parallel, you should be okay as long as neither battery is actually stuffed. If they are both in good condition you can hook them up in parallel without any hassles.

Jason

I've noticed on both my solenoid setups if I have different quality batteries I get one of the 2 overcharging and leaking acid out the caps, hence I replace the batteries together.

[murcod]

I wouldn't rely on the Jaycar / Dick Smith kit for extra starting current..... I know it's got the diodes within the FET's, but straight away you've lost 1.2v at least (voltage drop across the forward biased diodes). Plus the kit requires a fair amount of resisitance in the aux battery line for the circuit to function- so, basically there's going to be so much voltage dropped it will be next to useless for assistance.

Will this still work in charging that second battery. I have my main which is a 790 cca and a smaller 450cca that I want to use as a second battery to power fridge and compressor in the back. The main battery starts the bi$ch up first kick but will the second lower rated amp charge up off the main battery then

Yes the kit does all that. I've been running run for about 18mths (admittedly the aux battery doesn't get used all that much....) and it's been working perfectly. The aux doesn't get charged until the main is charged; plus the aux will have a limited current pumped into it if it's completely flat to make it last longer.

Do a search for "dual battery" on the Daihatsu forum and you should find pics of the kit (including the internals).

[Leprecaun]

Sweet Murcod, thanks for that went to Jaycar this morning and picked it up will be running it in the rig this arvo once I fit a new battery houseing in the back to prevent it from going flying when on my side (again ).