dual batt build up help

[lowndsie]

anyone in the western sydney area want to build up my jaycar kit for me???? after having a good look at it, it's just too much for me i think so i will have to pay someone reliable to do it......

[-Scott-]

PM chimpboy - his father builds them up, better than Jaycar ever intended. You might be able to organise an exchange deal?

Cheers,

Scott

[lowndsie]

thanx......pm sent.

[-Richo-]

ill build it for you for $100

Its easy mate just follow the instructions carefully, get thick wire to run to the main and aux terminal and really thick wire to run to your batteries (they only supply crappy thin wire with the kit).

Its easier than you think, just have a go.

[murcod]

ill build it for you for $100

Its easy mate just follow the instructions carefully, get thick wire to run to the main and aux terminal and really thick wire to run to your batteries (they only supply crappy thin wire with the kit).

Its easier than you think, just have a go.

You're actually supposed to use the thinner wire for the aux as it provides a voltage drop (feedback signal) for the control circuitry! It's in the instructions!!

[-Richo-]

ill build it for you for $100

Its easy mate just follow the instructions carefully, get thick wire to run to the main and aux terminal and really thick wire to run to your batteries (they only supply crappy thin wire with the kit).

Its easier than you think, just have a go.

You're actually supposed to use the thinner wire for the aux as it provides a voltage drop (feedback signal) for the control circuitry! It's in the instructions!!

So how come in the photos of the finished kit there is thicker wire used on the MOSFETs?

[-Scott-]

Because the people who built the unit for the photos don't read the text? I've got a mixture display in my Sigma, to help me tune the Webers. The text refers to the red LEDs being the lean end, but the colour photos show the red LEDs at the rich end of the scale. Took me a few months to work out WTF was happening - in the end I downloaded the manufacturer's datasheet for the driver IC and worked it out for myself.

A picture may be worth a thousand words, but when they tell lies...

But I used heavy wire anyway - my alternator can't deliver enough current to overload the two fets in parallel.

Scott

[-Richo-]

Well this was the photo in the instructions. Dont recall anything in the instructions about wire thickness just said to use what was supplied. Asked my old man who has about 35 years experience with electronics and he recommended to use the thicker wire too. Works fine though as i built it.

So maybe dont follow the instructions to the word

[murcod]

Mine's a little bit thicker- but the idea is the resistance in the aux wire gives a feedback voltage so the circuitry knows how much current is flowing. IIRC it's needed for the low aux voltage current limit to function correctly.

So did you go through the set up process for the low current limit? The instructions also give a big blurb on how to calculate out the resistance for the aux wire.

[-Richo-]

Mine's a little bit thicker- but the idea is the resistance in the aux wire gives a feedback voltage so the circuitry knows how much current is flowing. IIRC it's needed for the low aux voltage current limit to function correctly.

So did you go through the set up process for the low current limit? The instructions also give a big blurb on how to calculate out the resistance for the aux wire.

Your referring to the tests in the instructions? we set it up using a generator to test it, played around with the trim pot but nothing seemed to change. Got sick of it after about 2 hours of playing about, you really need a variable power supply to test it properly, so i just installed it into the car, only been in there for a few weeks but its charging the aux and kicking in when the main reaches about 13.7 volts. Will have to do some thorough testing, but if it shits itself ill probably just get one of those smart solenoids. Got it for nothing so im not really fussed.

My alternator hasnt been working properly (will be replaced today) so i will see how it goes under proper conditions. Though i recon the solenoid is the go as i am an advocate of the KISS principle, too many thinkgs can go wrong in the circuit, its not so bad on small trips, but if you traveling around Oz or something long, keep a spare solenoid and you'll be fine. I suppose you could keep a spare jaycar kit as well, depends on what you want to do.

[-Richo-]

Well since my alternator is fixed and charging properly now the unit doesnt kick in and charge the aux at all. I will redo the tests to see if its calibrated properly, but i think i am going to give this unit the flick, too much uneccesary bells and whistles to go wrong. Together with my dad we are going to make a simple isolator using relays, when the ignition is on a timer keeps them isolated for say 20 secs after start up and then they both get charged off the alternator. When the ignition is off both batteries are completely isolated. Its basically an automatic switch system that can be overriden manually if needed. With this method if a relay is broken you can manually connect the batteries in an emergency out in the middle of nowhere with a simple jumper lead until you get back home and can replace the relay.

Ill write up a step by step on how to build it and what parts etc so if anyone is interested they can do it themselves, i will open up another thread on it later on when we get around to it.