Which split charge system? Which battery?

Simon Barr wrote:

> ISTR that schotkkys vary from about 1V downwards depending on the current
> and the model of diode itself. I was using a fluke 77 on the diode test
> setting.

ANY silicon diode will have a Vf of 1V downwards, NO silicon junction
diode can have a Vf of less than 0.6-0.7 and NO Schottky will have a Vf
of less than about 0.2V !

So what the hell IS in the box ?

Steve

In article <[email protected]>, Steve Taylor wrote:
>
> ANY silicon diode will have a Vf of 1V downwards, NO silicon junction
> diode can have a Vf of less than 0.6-0.7 and NO Schottky will have a Vf
> of less than about 0.2V !
>
> So what the hell IS in the box ?
>
> Steve

Oh well, I was thinking it may just be an input that was split with a
schottky in each output, I was thinking schotkky as they (can) have a lower
forward voltage drop.

Maybe that's why I don't work in electronics anymore
--
simon at sbarr dot demon dot co dot uk
Simon Barr.
'97 110 300Tdi.

What if you parallel these? I've always wondered if the dreaded voltage
drop of diodes could be reduced in this way.

"Steve Taylor" <[email protected]> wrote in message
news:[email protected]...
> Simon Barr wrote:
>
>> ISTR that schotkkys vary from about 1V downwards depending on the current
>> and the model of diode itself. I was using a fluke 77 on the diode test
>> setting.
>
> ANY silicon diode will have a Vf of 1V downwards, NO silicon junction
> diode can have a Vf of less than 0.6-0.7 and NO Schottky will have a Vf of
> less than about 0.2V !
>
> So what the hell IS in the box ?
>
> Steve

Gordon Wedman wrote:
> What if you parallel these? I've always wondered if the dreaded voltage
> drop of diodes could be reduced in this way.

Not really.The graph of forward voltage drop against current looks like
a letter 'J'(its actually exponential) . Until there is a "reasonable"
current flowing (relative to the maximum continuous current), the
forward voltage could be said to be proportional to current, until the
voltage reaches 0.6 volts. Since its proportional to current, even if
you share it out, the total dissipation would remain the same or worsen
when split over multiple diodes


Steve

"Steve Taylor" <[email protected]> wrote

> > ISTR that schotkkys vary from about 1V downwards depending on the
current
> > and the model of diode itself. I was using a fluke 77 on the
diode test
> > setting.
>
> ANY silicon diode will have a Vf of 1V downwards, NO silicon
junction
> diode can have a Vf of less than 0.6-0.7 and NO Schottky will have a
Vf
> of less than about 0.2V !
>
> So what the hell IS in the box ?

It depends on the cost of the box. Probably a relay and the volt drop
is caused by the thin wires used to connect it.

If expensive then FETs could be used - Field Effect Transistors.

However I have a similar 'black box' (and yes it is black) with one
input for the alternator output and three outputs. One for the
existing starter battery and two for aux. deep discharge batteries.

But I have a Td5 Defender. From my previous experience of installing
split charge devices, the alternator output is a medium thickness
brown wire that goes from alternator direct to the battery. This wire
is cut and connected to the split charge input and one o/p.

Having received some help here, I've had a quick look under my
Defender. The alternator o/p goes direct to the starter. It looks
like I'm going to have to remove this wire from the starter and extend
it to the split charge box and thence to the battery.

But some have told me there are other problems.

Reg. (electronics eng.)

In article <[email protected]>, Reg wrote:
>
> It depends on the cost of the box. Probably a relay and the volt drop
> is caused by the thin wires used to connect it.
>
> If expensive then FETs could be used - Field Effect Transistors.
>

It's definitely some sort of semiconductor affair.

I've had it rigged up with a battery charger and two sealed lead acid
batteries in different states of discharge and it seems to work fine.
You can only use it to charge batteries with though, you won't be able
to pull any power from the alternator through the unit as its only rated
upto 8A.

--
simon at sbarr dot demon dot co dot uk
Simon Barr.
'97 110 300Tdi.

Thanks. I should have figured that out myself. Each diode requires the
same forward bias before it will conduct. Nothing like resistors in
parallel !

"Steve Taylor" <[email protected]> wrote in message
news:[email protected]...
> Gordon Wedman wrote:
>> What if you parallel these? I've always wondered if the dreaded voltage
>> drop of diodes could be reduced in this way.
>
> Not really.The graph of forward voltage drop against current looks like a
> letter 'J'(its actually exponential) . Until there is a "reasonable"
> current flowing (relative to the maximum continuous current), the forward
> voltage could be said to be proportional to current, until the voltage
> reaches 0.6 volts. Since its proportional to current, even if you share it
> out, the total dissipation would remain the same or worsen when split over
> multiple diodes
>
>
> Steve

intresting read .

Time to revive an old thread i've looking into split chargeing and at one point i found a system that has a button or something that you activate and it links both batterys together so if your main battery goes flat you can sort of jump start yourself, problem being i can't remember what it iscalled or where it is. any help?

what a waste of a post :doh: i've found it it was the IBS BM3