Diodes for 12v battery charging

I put in a 12v solar panel to charge up 2 ATV's and a mini tractor. Ran some speaker wire and battery clips to charge all of them in parallel. The tractor battery seems to not hold a charge very well. I'd like to add 3 diodes to protect the other 2 batteries in case at night with no input current, the low battery would siphon off power.

The setup is in a very remote location with no power lines and I've misplaced to specs for the panel and the 7amp regulator, but they both came from Harbor Freight. The bigger battery is 14 amp-hr, the 2 smaller ones are 10 amp-hrs.

Can someone please suggest an appropriate diode to purchase at Radio Shack or Fry's that will handle up to 7amp and not waste too much charging ability?

Reply to
Stumpy
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Assuming no broken batteries, just put them in parallel, the batteries will distribute present charge. One good quality diode in series with the panel is however important, because the panel itself is a bad quality diode, and will discharge the batteries in dark weather and at night.

Reply to
Sjouke Burry

we do that at work how ever, we have breakers on each battery with a large DIODE across each breaker leads.

Reply to
Jamie

I assume by the application that they are lead acid batteries. I am never comfortable charging LA batteries in parallel because of the different states of discharge when you put them on charge. Your batteries are close to the same capacity so I suppose that you can get away with it. You need to know the maximum charging current you will be using and select a diode with about a 50% safety margin. BTW: What is "speaker wire" What I really am saying is gauge your wire appropriately. Tom

Reply to
Tom Biasi

They are all lead acid batteries and physically about the same size. I was planning on putting a diode on each individual battery so that it could not be drained if another one took too much current. It's embarrassing that I don't remember, but I believe that the panel is 25 watts. The system is simply supposed to maintain charge on reasonably new batteries. The "speaker wire" is probably 14 or 16 gauge. I am unable to go check because of distance. Want to get parts before the next 3 day weekend. Can't run to the store very easily .:. any minor modification takes ~ 3 months to plan and try out.

Reply to
Stumpy

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from Fry's NTE6083

Make sure you mount these to a heat sink.

Also, not sure about your charging unit, it may be regulating voltage to a close degree. You'll get a slight drop in voltage to the batteries if the charge regulator does not ramp up to maintain current. Drop will be around .7 volts.

Reply to
Jamie

I don't even know how that 45volt rectifier could be used as a diode. This is a link to the regulator I have.

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Harbor Freight doesn't seem to carry the solar panel any more. I guess I'll just gamble with a 2 legged diode.

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Reply to
Stumpy

The picture of the rectifier shows a three-lead TO-220, but description says two-lead.

Drop will decrease to about 0.3V at low current when regulator goes into float voltage mode.

You might be able to cannibalize a Schottky rectifier from a computer power supply. Maybe a three-lead diode which can be used in parallel for even less voltage drop.

Here is the manual for a 7A Harbor Freight charging unit:

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Paul

Reply to
Paul E. Schoen

The answer to your question; "what type of diode", the best choice would be a shottky-barrier type as it has a lower forward volt drop than standard silicon.

If you are using a regulator to give the correct charging voltage for the battery, you will have to take into account the diode volt drop.

You quote a figure of 7A and say you are using "speaker wire", If I were you I'd check it isn't getting too hot when there's plenty of sun on the solar panels! Thicker wire would drop less voltage at full current and reduce power lost heating the wire.

Reply to
ian field

If you put diodes in series with the output of the regulator, the volt drop of the diodes might result in under-charging.

The ideal solution would be to give each battery its own regulator.

If you only want to use one battery at a time then you can connect the + terminal with an alligator clip, if you want the full capacity from all 3 batteries at once, you'll need output isolating diodes to feed the + terminals to your load - these diodes will need to be rated considerably more than 7A !!!

Reply to
ian field

I'm getting confused. The 3 batteries are in 3 separate vehicles. It might be convenient to have no diodes so that the other 2 batteries could act as "jumpers" when starting one, but then I would risk having one battery fail and drain the other 2 during a possible 2 month period with no attention. It seems safer to isolate the batteries from each other, yet allow a single solar panel to charge all 3 simultaneously.

I assume that a 25 watt panel would supply ~2 amps at 12 volts .:. the Radio Shack diode

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would be OK for charging and for reducing risk from an unexpected discharge. I was looking for some confirmation because I am a trial and error sort of fellow and an error can mean a bad trip and added expense.

Thanks for considering my problem.

Reply to
Stumpy

Many sights use generic images for their parts. They look at the TO-220 and think they're all the same.

AS far the manual, it really does not give much info to break down the circuit how ever, it does state (+.5) above 14V, so I think it should still charge the batteries, just maybe a little slower, which could be a good thing if it's left to keep the units at float.

Reply to
Jamie

Don waste your money on that part at Fry's, its not what you need. that is a protection diode and has nothing to do with what you need.

The one at Radio shack that you have pointed out would most likely work , even though its under rated by 1 amp and also, likely will have a higher forward voltage than what I pointed out.

I picked the one at Fry's because of your 7 Amp unit you have and keep the voltage loss down.

The diode from the shack will most likely get a little warm, the Fry's one, you can mount it to some AU to extract the heat and it's simple to hook up with an iron.

It's up to you.

Reply to
Jamie

Here is the data sheet:

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A recitifer is a diode. Look at the data sheet. The terminal marked 'K' is the cathode. This is the same as the banded end of a typical diode. The other lead is the anode.

That website is for their retail stores.

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is the main site, and there is another site for their "Inside Track Club" members. The site you referenced only lists the most popular items. They have a printed catalog with more items, as well.

This is only rated for six amps.

--
Greed is the root of all eBay.
Reply to
Michael A. Terrell

Thanks, I see it only has 2 leads. Now it makes sense to me. Paul pointed it out before but I needed to see the picture.

---snip----

I'm pretty sure that the panel can only supply ~2 amps.

I'd be happy to get 3 of the NTE 6083s for $4.80 at Fry's but Radio Shack is about 5 miles closer with a $2.50 4-pack of the

274-3631s. Don't need heat sinks either.
Reply to
Stumpy

The higher the current rating of the Schottky diode, the lower will be the voltage drop at a certain current. Here is a diagram of a typical 200W computer supply:

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The output rectifier is a D83-004 which is rated at 30A. At 6A, or 3A through each in parallel, the voltage drop is just about 0.35V.

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So it might be worthwhile to take apart some junk computer PSUs to get these diodes. However, you can get an MBR4060 from Mouser for $2.60 each. Dual 40A 60V.

Another idea to try is a set of three relays which take turns connecting the regulator to each of the three batteries. And you can add a small diode and resistor across each contact so that bateries not directly connected will still get a trickle charge. At least in this way the charger/controller will be able to interact with the battery in the way it was designed.

Paul

Reply to
Paul E. Schoen

I second that, any passive scheme can be defeated by a shorted cell in one battery. (or an open cell if you charge in series)

OTOH if you can get theee independant 14+V outputs from the solar panel you could set up each with an independant charge circuit. that would be another way to go, or just get three solar panels...

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Reply to
Jasen Betts

The 1N5822 40V 3A shottky-barrier diode would probably handle as much current as your speaker wire.

Personally, I'd go for a bit bigger safety margin like the devices here;

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If you want to charge 3 batteries in parallel, it would be better to feed each battery with its own regulator. If you want to split the current with a diode to each battery (from a single regulator) you will need a regulator that allows you to adjust the output upwards to compensate for the diode volt drops.

If each battery is used individually, that's all you need to do, if you wanted to use all 3 batteries in parallel, you'd need 3 more (much higher current) diodes to combine the three batteries into the load - it would sort of defeat the object of the first 3 diodes to then strap the 3 batteries together in parallel.

Reply to
ian field

Those relays sound like a fun project, but too sophisticated for me. Where do you guys post diagrams of your circuits? If Sci. E. B. is text only is there a companion group for binaries?

Reply to
Stumpy

I'll bet the relay project is something you could tackle, with a little help.

Regarding schematics, there are a number of possibilities:

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Spice lists a.b.s.e (alt.binaries.schematics.electronic) ASCII art

For example here's ascii art showing the diode isolation you mentioned:

------------ | Solar +|------+--->|---[Battery1]---+ | Controller | | | | | +--->|---[Battery2]---+ | Harbor | | | | Freight | +--->|---[Battery3]---+ | Model (?) | | | -|----------------------------+ ------------

Each approach has its pluses and minuses. For example the ACSII art above must be viewed in fixed font such as Courier.

Ed

Reply to
ehsjr

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