Diode replacment

"Paul Noisette"

** Please do not post in HTML !!!!!!!!!!!!

Need to use a diode to prevent two batteries seeing each other when connected in parallel. Not wanting to drop .6v with the diode is there something like a Mosfet I could use which I believe will only drop the voltage .2v? Needs to be able to handle 30A and preferably 40A for safety factor. Is never used for more than 30 minutes at a time.

** You totally fail to decribe what you are after or for what actual purpose - d*****ad !!

From the large amp numbers you possibly are on about 12 volt car batteries being operated in parallel.

If so - go see Jaycar.

If not, then TELL US WHAT YOU ARE DOING !!!!

..... Phil

Who says you dictate the posting rules Dipshit?

2 100ah 12v batteries that are used independently of each other. To power the invererter for short period with 280w on AC needs the batteries to be paralled. With the batteries at differing states of charge dont want 1 battery attempting to charge battery 2. Realise that one battery will supply more power till they equalise, but generally there is not much difference between the batteries. However the batteries cannot be directly connected.

Since found this article

Going on that article I would need a P-channel Mosfet as the negative cannot be isolated. In the Jaycar catalogue there is only a IRF9540N 100v 23A

can these be placed in parallel to increase the current rating? is there a higher powered P-channel Mosfet easily obtainable? will the Mosfet need a heat sink?

Take it the Gate is the negative power for switching, the Source is the 12v battery supply and the Drain is the power to the inverter. Is that correct?

Many thanks to those offering their help and expertise.

"Paul Noisette"

** Now you are posting in mid air = no context visible and no refeences to previous posts.

Says a lot about your thinking - or rather the lack thereof.

** SLA ( ie gell cell) or wet cells or other kind ??

Leaving this info out is really stupid.

** Kindly state why.

Your Q may disappear with the correct answer.

** This may be a false concern.

** Kindly state why.

Your Q may disappear with the correct answer.

** Purley reverse polarity protection for the load.

Something far better done with a relay and one, small diode.

...... Phil

Try this from Farnell. Make sure you use a big heatsink.

David

"KR"

Trust me mate, some posts in recent months have clearly shown that there are worse dickheads (call them what you may) on here than Phil.

** Am I being condemned here with faint praise ?????

Batteries have been paralleled in these sort of applications for decades without problems, that is probably why we need to know more about the application you need it for, as its a very unusual setup you are asking about.

** The OP has his reason - but it is not ours to know.

I wouldn't advise putting anything in series with them, it will only waste power and generate significant heat at the sort of currents you are talking about. With those sort of currents, you want as low a resistance as possible in the cables, connectors fuses etc.

** Water off a dope's back - I fear.

Nice try at concilliation , anyhow

..... Phil

No, not condemned, I would explain it as - yes you are rude at times, but I got used to it years ago, and unlike some on this group, I don't really care about it, but on the other side you do have knowledge of electronics (which is the purpose of this group) unlike some on here.

Yes, as I see more and more these days, efforts with many people are futile, better off saving energy for something else. This can get so frustrating. For example, trying to show someone how to do something, being constantly interrupted, asked irrelevant stupid questions that break concentration, and then having them go off and do the job some wrong way that doesn't work, and you have to go in and clean up the mess afterwards.

It is invariably considered bad form / netiquette to post html messages to Usenet.

Graham

-- due to the hugely increased level of spam please make the obvious adjustment to my email address

On Sun, 12 Jul 2009 12:29:42 +0800, "Alan Rutlidge"

:2 100ah 12v batteries that are used independently of each other. To power :the invererter for short period with 280w on AC needs the batteries to be :paralled. With the batteries at differing states of charge dont want 1 :battery attempting to charge battery 2. Realise that one battery will supply :more power till they equalise, but generally there is not much difference :between the batteries. However the batteries cannot be directly connected. : :Since found this article :

: :Going on that article I would need a P-channel Mosfet as the negative cannot :be isolated. In the Jaycar catalogue there is only a IRF9540N 100v 23A : :can these be placed in parallel to increase the current rating? :is there a higher powered P-channel Mosfet easily obtainable? :will the Mosfet need a heat sink? : :Take it the Gate is the negative power for switching, the Source is the 12v :battery supply and the Drain is the power to the inverter. Is that correct? : :Many thanks to those offering their help and expertise. :

There is a little more to using mosfets to isolate two heavy duty 12V batteries than you seem to imagine. Usually, these devices are incorporated into what are sometimes known as "Smart" dual-battery isolators, to distinguish them from the "dumb" diode-only type of isolator.

For example, here is a design by Dave Johnson which incorporates paralleled P-channel mosfets to give only 50mV drop, driven by a dedicated control IC.

Note that the mosfets must be on a decent heatsink to handle above 20A.

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tell me where you live you filthy stinkin rotten phil the turd = allison..

there i just posted in html to piss you ioff philthy phil.

there=20

safety=20

batteries=20

I would strongly suggest that drastic action not be used but by all means give him a call. He is listed in the Sydney White Pages under Phillip (Martin) Allison 8 Tintern Rd Ashfield NSW 2131 (02) 9799 8242

BTW when you have a look via Google Maps at the dingy flats he lives in have a look across the road and you will see a park and some public toilets. Nothing like being near to where the action is eh? ;-)

ALLMAN Park? Would the even let Phil in?

--
You can\'t have a sense of humor, if you have no sense!