Schottky Battery Paralell setup... How?

Batteries, Chargers, and Battery Management Systems.
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fechter   100 GW

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Re: Schottky Battery Paralell setup... How?

Post by fechter » May 30 2008 2:22pm

According to the datasheet, the dissipation at 40 amps will be around 27 watts.
In actual riding, you probably won't be running at 40 most of the time, so dissipation will be less.

Imaging stuffing a 25W light bulb into a little box and letting it run for a while. It's going to get pretty hot. Any amount of air circulation around the fins will help tremendously.

The heat sinks look very good. Potting in epoxy sounds good. Make sure to test it before pouring the epoxy!
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Re: Schottky Battery Paralell setup... How?

Post by TylerDurden » May 30 2008 2:45pm

I'm not sure about the potting. I rarely see high power/temperature stuff potted. Power transistors, big diodes, etc., benefit from air-circulation.

Potting is good for keeping stuff from rattling about, but if heat is a concern, I'd skip it.

:?
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Re: Schottky Battery Paralell setup... How?

Post by fechter » May 30 2008 2:54pm

Potting will be good to prevent the wires from breaking the leads off the diodes and will also make it waterproof.

His plan was to only bury the diode body and leads in epoxy, with the fins sticking out for cooling.
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Re: Schottky Battery Paralell setup... How?

Post by michaelplogue » May 30 2008 2:55pm

The reason I'm thinking of potting is because that is what it looks like ebikes.ca did with theirs.

Image

I figured the computer chip heat sinks will allow better heat dispersal than theirs (though they may have been using the case itself as the heat sink)
.

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Re: Schottky Battery Paralell setup... How?

Post by michaelplogue » Jun 03 2008 6:58pm

Well, I've received everything but the heatsinks, so I started assembling my first unit. Gave it a test and is working fine (I was worried about heating it up too much while soldering). These particular diodes are giving me a voltage drop of 0.4 so I think these will do fine.

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Re: Schottky Battery Paralell setup... How?

Post by Tiberius » Jun 04 2008 3:08am

Hi Michael,

0.3 to 0.4 is what you might expect from a Schottky at low current. Normal PN junction diode drop is 0.6; the reason for using Schottkies in this application is the lower forward drop. But at high currents the voltage drop will rise; some of the datasheets have them up to 1 V at 30 or 40 A.

I just saw this system for using FETs with a control IC to simulate diodes, but with no forward drop
http://www.linear.com/idealdiodes
At first glance its OTT, but it could save dozens of Watts on a bike, more on some EVs.

Nick

Edited to add: I started a thread on the ideal diodes; I thought they deserved it.

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Re: Schottky Battery Paralell setup... How?

Post by cee » Jun 07 2008 3:19pm

hello would it be ok to parallel
1)nicads 36v 8ah with sla 36 v 10ah or sla 36 v 4.5 ah
or
2)nicads 36v8ah with nimh 36 v 4.2 ah

with schottky diode setup of your diagram

nicads are the primary batteries and just wanted a extra boost

current setup is nicad 36v 8ah and 36 v 10ah sla i use one at a time currently with switches
thank you very much

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Re: Schottky Battery Paralell setup... How?

Post by Tiberius » Jun 07 2008 6:18pm

Hi Cee,

Yes, those combinations would be ok.
Basically with the Schottky diodes in place- one diode for each battery pack - you can parallel almost anything.

Nick

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Re: Schottky Battery Paralell setup... How?

Post by cee » Jun 07 2008 7:18pm

hello Tiberius thank you so much for replying i just orderd the schottky diodes from digi-key thanks again

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Re: Schottky Battery Paralell setup... How?

Post by Tom_D » Jun 08 2008 11:49pm

Hi, I am new to the forum, trying to combine a 48v SLA pack to a 48v A123 pack in parallel with a Schottky Diode.

Here is the schottky I used: Rated 120V, 30A each leg
http://search.digikey.com/scripts/DkSea ... %2F45GI-ND cost $3.14
with specs:
http://www.vishay.com/docs/88976/v60120c.pdf

I removed center (common cathode) and soldered 10awg wire output + to the tab (which is also common cathode). Soldered 10awg wire to + inputs on outside legs. Wire size was overkill, but I want to be able to use this under higher usage down the road. Used a plastic toothpick box with 3 drilled holes and (2) sets of 2 part black epoxy from Ace hardware (3.99each). Hardest part was carefully placing diode in box.

Tested fine, .1v forward voltage drop at rest. Specs show only .75v drop at max rated amperage.


Here are some pics: This first one is with center pin common cathode removed (for ease of soldering).
Schottky Diode_1.JPG
Schottky Diode_1.JPG (153.37 KiB) Viewed 723 times
Schottky Diode_2.JPG
Schottky Diode_2.JPG (129.78 KiB) Viewed 718 times
Schottky Diode_3.JPG
Schottky Diode_3.JPG (119.81 KiB) Viewed 716 times
Schottky Diode_4.JPG
Schottky Diode_4.JPG (138.47 KiB) Viewed 714 times
I will hang this outside of the battery bag to help dissipate heat.
Total cost under $12.

Hope this helps,

Tom

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Re: Schottky Battery Paralell setup... How?

Post by Link » Jun 09 2008 12:12am

:!:

That epoxy stuff...where did you get it and how much? :D
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Re: Schottky Battery Paralell setup... How?

Post by Tom_D » Jun 09 2008 1:01am

Link wrote::!:

That epoxy stuff...where did you get it and how much? :D
This was black 2-part epoxy I got at our locaql Ace hardware for $3.99. I needed 2 of them. I think it said for use with steel, metal, etc. but i figured was just marketing and that it didn't really have any metal particles in it. When hardened, I tested for conductivity and it doesn't conduct. It said it was good up to 250 degrees F.

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Bike: wally world 26" Roadmaster mtn
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Re: Schottky Battery Paralell setup... How?

Post by Link » Jun 09 2008 1:07am

Hmm, I'll have to snoop around for something similar. That's exactly what I need for coming up with a custom connector block. :)
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Re: Schottky Battery Paralell setup... How?

Post by Toorbough ULL-Zeveigh » Jun 09 2008 3:41am

I've used Devcon plastic steel epoxy & J-B Weld I think is the most common.
Altho if it's for anything much larger I'd go with just a potting compound that would work out cheaper.
I'm pretty sure there are iron particles in it, it just doesn't conduct cuz the particles are fine enuf that they're completely encapsulated by the resin.
You could probably make your own using regular epoxy & iron filings.
I've never done it with iron but have used flour mixed in with epoxy to create a stronger composite material when repairing plastic radiator tanks.
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Re: Schottky Battery Paralell setup... How?

Post by billman » Jun 12 2009 11:24pm

OK, first off I work in medicine and have a degree in English literature, so I know little about electronics. I've read this thread but see directions for two batteries only and am too ignorant to extrapolate to more.

I have four 36V 10Ah LiFePO4 batteries arriving tomorrow from E-Bike Kit. I'm using them on a Stokemonkey, whose controller limits current draw to 20 amps. Each battery has its own port for its own charger.

Having a heluva commute, I would like to run all four in parallel, using Schottky diodes to protect the packs from any imbalances.

I also plan to use all four chargers at once. I plan to cut off the charging plugs and leave them permanently plugged into the batteries, with the other ends terminating in a block of Anderson PP's that would plug into a mating block of PP's coming from the chargers.

So here's the current state of my ignorance:

1. Do I use one diode and wire it between the + and - of the first battery in the parallel string (assuming the terminals of the last battery in the string attach to the controller)? i.e. I need a schematic!
2. Which diode? This one seems to offer appropriate specs: http://tinyurl.com/mc7sqj
4. Or do I need a diode in between each battery? (3 diodes?) How do I wire the 3 leads in this case? I need a schematic!
5. Do these diodes in this application need heat sinks?
6. Can I leave the packs hooked up in parallel (but switched off from the controller) during the charge phase if I simply plug each pack into its dedicated charger via my Anderson plug?

Thanks for any help.
Bill in San Francisco

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Re: Schottky Battery Paralell setup... How?

Post by Tiberius » Jun 13 2009 2:20am

Tom_D wrote:
Link wrote::!:

That epoxy stuff...where did you get it and how much? :D
This was black 2-part epoxy I got at our locaql Ace hardware for $3.99. I needed 2 of them. I think it said for use with steel, metal, etc. but i figured was just marketing and that it didn't really have any metal particles in it. When hardened, I tested for conductivity and it doesn't conduct. It said it was good up to 250 degrees F.

Tom
Tom,

What current are you running?
There will be some heat generated in the diodes and that epoxy is not very good at conducting heat. You can get specially loaded stuff that has three or four times the thermal conductivity, but its still not very good.

One thing I've done successfully in the past is to bolt the diode to an aluminium plate and then pot it. That way the heat is spread out before it has to pass through the epoxy.

Nick

Edit: Oops, must read the small print. Just realised I've replied to a year old post. Still, the advice stands.

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Re: Schottky Battery Paralell setup... How?

Post by Tiberius » Jun 13 2009 2:57am

billman wrote:OK, first off I work in medicine and have a degree in English literature, so I know little about electronics. I've read this thread but see directions for two batteries only and am too ignorant to extrapolate to more.

I have four 36V 10Ah LiFePO4 batteries arriving tomorrow from E-Bike Kit. I'm using them on a Stokemonkey, whose controller limits current draw to 20 amps. Each battery has its own port for its own charger.

Having a heluva commute, I would like to run all four in parallel, using Schottky diodes to protect the packs from any imbalances.

I also plan to use all four chargers at once. I plan to cut off the charging plugs and leave them permanently plugged into the batteries, with the other ends terminating in a block of Anderson PP's that would plug into a mating block of PP's coming from the chargers.

So here's the current state of my ignorance:

1. Do I use one diode and wire it between the + and - of the first battery in the parallel string (assuming the terminals of the last battery in the string attach to the controller)? i.e. I need a schematic!
2. Which diode? This one seems to offer appropriate specs: http://tinyurl.com/mc7sqj
4. Or do I need a diode in between each battery? (3 diodes?) How do I wire the 3 leads in this case? I need a schematic!
5. Do these diodes in this application need heat sinks?
6. Can I leave the packs hooked up in parallel (but switched off from the controller) during the charge phase if I simply plug each pack into its dedicated charger via my Anderson plug?

Thanks for any help.
Bill in San Francisco
Bill,

Here's the schematic you need.
4diode.gif
4diode.gif (6.02 KiB) Viewed 1136 times
And to answer the other questions.
2. Its not critical, more or less any diode with the current rating and a package you can bolt to a heatsink, such as TO-220 or TO-247.
5. Yes.
6. Yes, but do not connect the charger leads to each other, keep them separate in your stack of connectors. It is likely that the +ve charger lead is connected to the +ve power lead inside the battery.

You could also discuss this with the sellers of the batteries. If its Justin at ebikes.ca, then he says some batteries have features in the BMS that mean you don't need the external diodes.

At 20 A you are definitely going to need a heatsink of some sort.
Let me refer you to this thread, http://endless-sphere.com/forums/viewto ... 14&t=10471 which is about another way to do it - but buried in there you will find a graph showing the heat generated at various currents.

Nick

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Re: Schottky Battery Paralell setup... How?

Post by Tom_D » Jun 13 2009 3:41am

Tiberius wrote:
Tom_D wrote:
Link wrote::!:

That epoxy stuff...where did you get it and how much? :D
This was black 2-part epoxy I got at our locaql Ace hardware for $3.99. I needed 2 of them. I think it said for use with steel, metal, etc. but i figured was just marketing and that it didn't really have any metal particles in it. When hardened, I tested for conductivity and it doesn't conduct. It said it was good up to 250 degrees F.

Tom
Tom,

What current are you running?
There will be some heat generated in the diodes and that epoxy is not very good at conducting heat. You can get specially loaded stuff that has three or four times the thermal conductivity, but its still not very good.

One thing I've done successfully in the past is to bolt the diode to an aluminium plate and then pot it. That way the heat is spread out before it has to pass through the epoxy.

Nick

Edit: Oops, must read the small print. Just realised I've replied to a year old post. Still, the advice stands.
Combined: 40A. The potted shottkey's I made barely get warm.
Tom
Bike: wally world 26" Roadmaster mtn
Trailer: Bob
Motor: front Clyte 5305
Controller: LYEN 124115 HV
Charger: Soneil 4808 SRF (onboard), parallel charging (4) 48V blocks, NO BMS
Batt: 84s2p Toyota Prius Gen III
Dashboard: Cycle Analyst

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Re: Schottky Battery Paralell setup... How?

Post by Tom_D » Jun 13 2009 3:51am

billman wrote:OK, first off I work in medicine and have a degree in English literature, so I know little about electronics. I've read this thread but see directions for two batteries only and am too ignorant to extrapolate to more.

I have four 36V 10Ah LiFePO4 batteries arriving tomorrow from E-Bike Kit. I'm using them on a Stokemonkey, whose controller limits current draw to 20 amps. Each battery has its own port for its own charger.

Having a heluva commute, I would like to run all four in parallel, using Schottky diodes to protect the packs from any imbalances.

I also plan to use all four chargers at once. I plan to cut off the charging plugs and leave them permanently plugged into the batteries, with the other ends terminating in a block of Anderson PP's that would plug into a mating block of PP's coming from the chargers.

So here's the current state of my ignorance:

1. Do I use one diode and wire it between the + and - of the first battery in the parallel string (assuming the terminals of the last battery in the string attach to the controller)? i.e. I need a schematic!
2. Which diode? This one seems to offer appropriate specs: http://tinyurl.com/mc7sqj
4. Or do I need a diode in between each battery? (3 diodes?) How do I wire the 3 leads in this case? I need a schematic!
5. Do these diodes in this application need heat sinks?
6. Can I leave the packs hooked up in parallel (but switched off from the controller) during the charge phase if I simply plug each pack into its dedicated charger via my Anderson plug?

Thanks for any help.
Bill in San Francisco
Bill. first of all, welcome to the forum!
I would make damed sure that the chargers will not drain down the battery packs while left connected. Also, each shottkey diode will have some forward voltage drop. I can't tell what that is for the one you linked, but you want to pick ones that are as low a voltage drop as possible. Check my year-old posts above on the construction of a rugidized potted schottkey.

Tom_D
Bike: wally world 26" Roadmaster mtn
Trailer: Bob
Motor: front Clyte 5305
Controller: LYEN 124115 HV
Charger: Soneil 4808 SRF (onboard), parallel charging (4) 48V blocks, NO BMS
Batt: 84s2p Toyota Prius Gen III
Dashboard: Cycle Analyst

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Re: Schottky Battery Paralell setup... How?

Post by Tiberius » Jun 13 2009 8:47am

Tom_D wrote:
Combined: 40A. The potted shottkey's I made barely get warm.
Tom
Hi Tom,

If that's 40 A continuous, then there will be about 30 W of heat generated. The outside of the assembly might only be warm, but think what the junction temperature inside the diode might be.

Nick

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Re: Schottky Battery Paralell setup... How?

Post by billman » Jun 13 2009 11:45am

Thank you so much, Nick and Tom. The schematic is EXACTLY what my brain needed to make sense of this.

Justin did indeed say that I did not need diodes with LiFePO4 chemistry batteries. However, Jason and E-Bike Kit who sourced the batteries thought they were a good idea. For the amount of money I have tied up in these puppies, I'm gonna err on the side of caution.

And all this is just to get me up and running, while I wait for the Ideal Diodes to become available!

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Re: Schottky Battery Paralell setup... How?

Post by Tom_D » Jun 13 2009 12:13pm

Tiberius wrote:
Tom_D wrote:
Combined: 40A. The potted shottkey's I made barely get warm.
Tom
Hi Tom,

If that's 40 A continuous, then there will be about 30 W of heat generated. The outside of the assembly might only be warm, but think what the junction temperature inside the diode might be.

Nick
Hey, Nick, point well taken. To anyone reading, you should probably then follow Nick's construction note a few posts back and first mount the shottkey diode to an aluminum plate before potting, to extend service life of diode.

(Note: I don't use Shottkey's now. With the NiMh Prius batts I presently use, I am 100% parallel in a 42s2p for both discharging and charging - works great! :mrgreen: but that's OT - I will post on Prius Batt thread)

Tom_D
Bike: wally world 26" Roadmaster mtn
Trailer: Bob
Motor: front Clyte 5305
Controller: LYEN 124115 HV
Charger: Soneil 4808 SRF (onboard), parallel charging (4) 48V blocks, NO BMS
Batt: 84s2p Toyota Prius Gen III
Dashboard: Cycle Analyst

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