Thread: Questin re: amps from a battery

its easy to work out...

Batteries have a CCA rating.... and a AH rating

Say its a 650 CCA and 150AH

Then its got 150 Amp hours.. thats 150 amp draw for an hour or 150 hours it will take to flattern it with 1 amp.

So in your case... 3 amps on a 150AH is 50 hours....

You'll be drawing about 20 amps for those two things. Nice thick 30 amp wire is what I would use should be OK. But depends on what else you will have drawing on your power eg: air con, 2 way, fridges etc.

20 amps is a lot - that's like having all your headlights and spotties on high beam. Using Clarkie's model you should get about 9 hours out of the battery ( not charging ) but its likely to be way less than that because the battery will drop below the voltage needed to run the PC well before then.
But if you are mostly running it with the engine on and the alternator charging you should be OK. Just turn it off if you're leaving the car for any length of time.
If you're just using a high amp ( 200 Amp) relay and good thick wires the alternator should be putting more into the second battery than you're taking out.
I'm sure Drivesafe will contribute here anyway - he's da man.

200amp relay? So I don't just bolt it to the terminal with a nice big inline fuse?

As it's not fitted yet I expect only to be running this car-puter & screen from the second battery but I thought with the dual battery solenoid type kit once it has power it will draw from both batteries?

Anyhow it will more or less only run when the engine is going and I'm OK with turning it off for lunch stops :-)
The only add-ons I have really are a couple of cheap spotties & a UHF that run from the starter battery, (and air-con).

As I mentioned just checking at the moment coz if this screen goes cheap I will buy it but don't want to throw my money away on something that draws too much current.

Originally Posted by HangOver

200amp relay? So I don't just bolt it to the terminal with a nice big inline fuse?

.

Little confused now -sorry if I confused you - its just you said your second battery was wired up via a solenoid - solenoid, relay are the same thing basically. Normally those big round ones used for connnecting your first and second battery are rated at 200 amps.

While running the alternator should cope. I say should, because, well, I haven't seen the vehicle and dont know how good everything is (everything matters, from brush condition to belt tension). For a 20 A draw, as what you've described is, you'll need 12.5-10.5 guage cabling depending on the distance you need to run. I'd lean towards 10.5 on account that you can add to it if you want to later. It'll cope to roughly 40A.

I'd say definately run from your secondary battery...and probably even advise you to use a deep cycle high AH battery as the secondary.

In terms of what cabling to use between Primary-solenoid-secondary batteries you'll need battery&starter cable (called that mainly coz it's larger.) 8 guage is normally suffient for a charging and load circuits on a secondary battery. If you actually wanted to use that battery to aid starting much larger cable would be required. 8 guage will do up to around 80 A.

Just curious, is your solenoid a voltage sensitive solenoid? As most dual battery ones are these days... If so, once the alternator is charging the system is connected, hence it shouldn't be drawing anything from the batteries...that is what the alternator is for! To supply loads while the engine is running!

Hopefully I haven't been too useless!

Originally Posted by Relay

run from your secondary battery...and probably even advise you to use a deep cycle high AH battery as the secondary.

Being a bit cash strapped I go this system whole from another vehicle so the second battery will be whatever is in the garage until it dies or doesn't do the job.

Originally Posted by Relay

Just curious, is your solenoid a voltage sensitive solenoid?

Ermmmmm maybe?
All I know about the solenoid is it's a 12v ingram 841151
I'm just hoping it'll do the job if not I'll get an new one.
It has 4 terminals the centre two I believe to be the solenoid power on/off? I was going to either put a switch on it or maybe if I feel adventerous wire it on/off with the ignition. Prob just a switch though.

Originally Posted by Relay

Hopefully I haven't been too useless!

Been very helpful mate especially the wire sizes, as I said it came pretty much complete and the battery wire is size "THICK" but I need to get wire to power the car-puter from the battery and the terminals replaced they look a bit 'wobbely'

Steve mate the system sounds the same as mine 200amp relay to conect/isolate the 2 batterys imrunning a supercharge gold top mait free for main cranker and a allrounder as the secondary which is a deepcycle with cranking ability the solinoid is switched by the power at the coilas the ignition is on it joins the 2 batts when the ignition is off it isolates em .....

My only prob with this is that when the ignition is on and the engin running the batts are joined up and the voltage between the both of em is enough to trick the alternator that theres enough voltage there and slows the charging process imlookin at fitting an SC40 from drivesafe as it conects to the alternator and to the 2 batts ans it controlls the power coming from the alternator this way it will charge both batterys fully quicker and will be benificial to the allrounder in the long run