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Discussion Starter · #1 ·
I am using two Aristo Li-ion batteries in parallel and an Aristo Train Engineer 27mhz for the battery car.  Some time ago I saw where a diode was recommented to be put in the + wire of each battery.  What number diode should I use?  I think diodes are directional.  How does one tell which way to place such a diode?  I have not looked at a diode for 20 years.  :)

Frank Barnard 
 

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You can use silicon diodes. They need to big enough to handle the current that is to be pulled by the locomotive. If you hook the diodes in the plus lead of the batteries, you would place the end without the stripe towards the batteries.

A silicon diode will drop about .7 volts  in this circuit.
 

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Discussion Starter · #4 ·
Using one battery don't use a diode.  Two Li-ion batteries can be a problem.  Li-ion batteries have had a reputation of fire and explosion.  I have not had such a problem but for several year there have been warnings of such things.  With two batteries in series the + sides are together.  If one battery has a charging problem  the other battery could drain back to the weak or damaged one.   Being that Li-ion batteries have such a great amount of power in a little package I don't want any possible chance of releasing this energy destroying a battery or other items or yet myself.   Now the diodes stops the electrons from flowing from one battery to the other in the above situations.  The flow is in only one direction through a diode.  I am not an electronics person. I am  just trying to play it safe. 

Frank Barnard 
 

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Discussion Starter · #5 ·
Bill, do I need a 1N4002 diode? or some other size (number)? I mention this number because Dallee uses it in the SD45 sound hook up.    The battery car is used with this sound and engine.
Frank Barnard
 

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Frank,

A 1N4002 has only a 1amp capacity. All the 1N400x are general purpose 1amp diodes. The last digit is the voltage rating so a 1N4001 is 1amp 50V and a 1N4007 is 1amp 1000V.

The li-on battery will output around 2amp at 22V so you need something around 3 or 4 amps and 30 or 40V. Like a 1N5404 (3amp 400V) or a SR504 (5amp 40V)
 

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/DesktopModules/NTForums/themes/mls/emoticons/angry.gifthe diode will only prevent power draining into the battery that the diode is allowing current to flow from so the upstream battery has no protection, right? that is why i made harnesses that  ican unplug and chrge each battery pack seperately
 

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Discussion Starter · #9 ·
Greg Elmassian has a great multi page write up on the diode on the Aristo Craft forum were I asked a question about the diode. I found that the PIV after the number 6amp 600PIV means peak invers voltage which is the safty factor for the electron back push into the diode. The Aristo Li-ion battery is 21.5 volts and 2 amps. So this battery is 2 amps and the diode will handle up to 6 amps. The 600 tells me the diode should handle up to 600 volts like a safty valve and the battery has 21.5 volts. Also place the diode with the ring toward the battery. See guys you all taught me something. But I still am no electronic engineer. Thank you. Next, I might need some help wiring the Dallee sound in the SD45.
Frank Barnard
 

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Why use diodes? Well, if one battery is fully charged and the other is not, hooking the 2 batteries in parallel without diodes would cause a large rush of current from the more fully charged battery to the other. With diodes in the circuit, you will run from the most highly charged battery until they are of equal voltage then, both batteries will feed the locomotive at the same time.

The 1N4002 is rated at 1amp. That is not enough to run an SD-45. The Radio Shack 276-1141 is rated at 3A  and 50PIV.  I would say that 3A is the smallest that you should use.  That way, each battery can supply 3A to the locomotive without  damaging the diodes.

I use Shottky diodes in my equipment. Take a look at Mouser electronics, part #512-SB530. It is a 5AMP Shottky diode. It will drop a maximum of .55V instead of the .7V of a silicon diode. Also, being raqted at 5amps, it will easily handle the power requirements of your SD-45. By the way, they are only $ .46 each.
 

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Posted By Pipertwo on 01/11/2008 11:03 PM
Also place the diode with the ring toward the battery.
Frank Barnard

Maybe, maybe not. It depends on which wire it is connected to.

If the diode is connected to the ground wire (-ve) then ring is towards the battery (the diode arrow points towards the battery)
If the diode is connected to the live wire (+ve) then the ring is away from the battery (the diode arrow points away from the battery).

On the Aristo li-on batteries, the red wire is +ve, the black wire -ve.
 

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Unless the Crest Li bateries have internal diodes, one diode will not be enough to prevent any chance of backfeeding from one battery to the other.
You will need two.
Use one on each +ve lead, usually red, with the band pointing away from the battery.
Join the two leads from the two banded ends into a common +ve.
Join the two -ve leads, usually black into a common ground.
 

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Just to round out the discussion, the main reason to isolate the batteries with diodes is if/when you have one cell in a pack fail. Often when a cell fails, it turns into a dead short. Now you have a pack that has a charging voltage lower by about 3 volts. Now the undamaged pack will overcharge the damaged pack. This will at least cause overheating, and in the worst case, a fire. Li-ion batteries do not like being overcharged.

So to me, it's a necessary safety precaution. Yes, many people will tell you they have used batteries for X years and never a problem. The risk of damage to yourself, your trains, or your house or family is there. My position is that these diodes are cheap insurance.

Regards, Greg
 

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Take 2 batteries. Connect the negative leads together.

Connect a diode to each battery, with the band away from the battery.

connect the free ends of the diodes together, this is your postive terminal.

Regards, Greg
 

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Don't forget to tell him how to charge this;)
 

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Posted By rpc7271 on 01/15/2008 1:30 PM
Can someone please provide a diagram with 2 Aristo li-ion batteries please.


Pictured is an Evans power car with a TE, two charging plugs, a Four Pole Double Throw center-off toggle switch, and two Aristo-Craft lithium-ion batteries. My diodes arrived too late to be included in this power car, but will be added before the next running season.
 

 
The charging plugs (2-pin plugs) are hot glued to the bottom of the frame and fastened to the right column of switch tabs.
 

 
The two lithium-ion batteries are fastened to the center tabs of the switch. The diodes will be added in the red wires with the band facing away from the batteries and towards the switch tabs.


 
Toggling the switch rearward towards the battery packs will connect each charging plug to its corresponding battery pack. This allows the batteries to be independently charged by plugging in two Aristo-Craft battery chargers. Charge time is four hours or less.
 
The TE is fastened to the left column of switch tabs.
 

 
A red jumper joins the positive tabs of the switch, and a black jumper the negative tabs. When the switch is toggled forward towards the TE and MU plug (not shown), this battery packs are joined in parallel to power the TE.
 

 
The complete construction log of this http://ovgrs.editme.com/EvansPC4th Generation Power Car can be viewed by clicking on the link.
 
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