diode needed for a 12 volt lithium battery.

Thread Starter

mdr14

Joined Mar 5, 2021
9
Because of the limitations of the circuit board on a 12 volt lithium battery, I need to jumper the negative side of the capacitors directly to the negative terminal. The battery will be in a motorcycle. I need to use a diode, because I want to have a one way out flowing circuit for the ground. When charging, I want the ground charge to go through the circuit board.

I do not know enough about diodes, and there is too much information out there for me to make a determination easily. SO I am seeking some guidance.

The diode should be able to handle at least 25 amps. No or minimal voltage or current drop. The reverse voltage is not that much a factor. A little will be fine.

Thanks for any input.
 

BobTPH

Joined Jun 5, 2013
3,658
A diode between a circuit and the negative battery terminal would be a bit unusual. Please explain better what problem you are trying to solve.

Bob
 

Thread Starter

mdr14

Joined Mar 5, 2021
9
A diode between a circuit and the negative battery terminal would be a bit unusual. Please explain better what problem you are trying to solve.

Bob
Thanks for replying. Yes, it is unusual to place a diode in a negative circuit. However, that is what I need to happen.

I am not knowledgeable enough about the different types of diodes and knowing what the specs mean to determine what type of diode will suit my needs.
I need a diode that won't restrict the voltage or current. I need it to be able to work in a 12 volt circuit , but when charging the voltage could be as high as 14.5 volts.

I am strictly bypassing the circuit board and running the negative side of the capacitors directly to the negative terminal on the battery. The need for the diode is that I want the charging to go through the circuit board and not charge the capacitor cells direct. If the circuit board shuts down the battery, I need to bypass that possibility by keeping the battery still active. while retaining the protection under charging conditions.
 

Thread Starter

mdr14

Joined Mar 5, 2021
9
A Schottky diode will typically have a lower voltage drop than a regular silicon diode. Go take a look at Mouser and you’ll find lots of options.
https://www.mouser.com/Semiconducto...ctifiers/Schottky-Diodes-Rectifiers/_/N-ax1mj

I’m a little confused about what you’re doing, and a little skeptical that a diode is the best solution. Maybe you could post a drawing?
Yes, mouser is a great resource, however, with my limited knowledge, I do not know what the specs mean on the different diodes. So I am having trouble picking one that will work.
 

Papabravo

Joined Feb 24, 2006
16,792
Thanks for replying. Yes, it is unusual to place a diode in a negative circuit. However, that is what I need to happen.

I am not knowledgeable enough about the different types of diodes and knowing what the specs mean to determine what type of diode will suit my needs.
I need a diode that won't restrict the voltage or current. I need it to be able to work in a 12 volt circuit , but when charging the voltage could be as high as 14.5 volts.

I am strictly bypassing the circuit board and running the negative side of the capacitors directly to the negative terminal on the battery. The need for the diode is that I want the charging to go through the circuit board and not charge the capacitor cells direct. If the circuit board shuts down the battery, I need to bypass that possibility by keeping the battery still active. while retaining the protection under charging conditions.
Your needs are seemingly incompatible with the operation of a diode. You can't get something for nothing and the price you pay with a diode is a voltage drop across it that increases as a function of the current through it. If you have a 12 volt circuit and you need all 12 volts, then a diode won't work for you. As is the case with many posters, they imagine that their words carry the precise meaning(s) of what they are thinking. This is hubris and delusion on a massive scale. The schematic diagram is the ONLY way to explain what is going on in a circuit and what you are trying to do. With that diagram we can understand the problem and offer solutions. Without it we have to guess and will most likely guess wrong.
 

Thread Starter

mdr14

Joined Mar 5, 2021
9
You did not say any details about the battery, its circuit board, its capacitors, its charger or why you need a diode.
it is a lithium LTO battery. so the cells are LTO. Any charger can be used. The ground currently goes through a series of mosfets. I want an active one way ground from the junction of cell negatives straight to the negative terminal, bypassing the mosfet circuit, so there is always an active ground. But, I do not want active charging through that bypass, hence the diode.

So the question remains, which diode do I need,that will handle my requirements.
 

Thread Starter

mdr14

Joined Mar 5, 2021
9
Your needs are seemingly incompatible with the operation of a diode. You can't get something for nothing and the price you pay with a diode is a voltage drop across it that increases as a function of the current through it. If you have a 12 volt circuit and you need all 12 volts, then a diode won't work for you. As is the case with many posters, they imagine that their words carry the precise meaning(s) of what they are thinking. This is hubris and delusion on a massive scale. The schematic diagram is the ONLY way to explain what is going on in a circuit and what you are trying to do. With that diagram we can understand the problem and offer solutions. Without it we have to guess and will most likely guess wrong.
I appreciate the reply. and I do get where you are coming from. However, you are making it way more complicated that is needed. I am not designing a rover to be sent to mars that needs the type of precision you are suggesting. All I need is some help determining the type of diode I need and what specs that diode will need to have.. It is okay if there are some takeaways. It is ok that the voltage and or current drop a smidge. It is ok that there be some reverse voltage.

If I knew what the specs represented on the diodes I have looked at, this would be easy for me.

So for me, it is get the information from the group mind, or spend however long it takes to educate myself more on what I need.

Thanks a bunch!!
 

Papabravo

Joined Feb 24, 2006
16,792
it is a lithium LTO battery. so the cells are LTO. Any charger can be used. The ground currently goes through a series of mosfets. I want an active one way ground from the junction of cell negatives straight to the negative terminal, bypassing the mosfet circuit, so there is always an active ground. But, I do not want active charging through that bypass, hence the diode.

So the question remains, which diode do I need,that will handle my requirements.
I cannot for the life of me visualize WTH you are talking about. Draw a simple schematic so we can get on with it.
 

wayneh

Joined Sep 9, 2010
17,153
So the question remains, which diode do I need,that will handle my requirements.
I could choose a diode for you at Mouser but I share the concerns of @Papabravo. Be aware that any diode will get hot when significant current flows through it. That means a big heat sink will be required in your case. Do you have room for that?

Oh what the hell. Here's the cheapest Schottky diode I see at Mouser that seems to meet the current rating you need (≥25A).
https://www.mouser.com/ProductDetail/ON-Semiconductor/MBR2545CTG?qs=3JMERSakebrE5P2V2lYPnQ==

This one is beefier and still cheap.
https://www.mouser.com/ProductDetail/ON-Semiconductor/MBR60H100CTG?qs=3JMERSakeboxv3Jefnz5qQ==

You're free to spend more to get evermore robust specs. For instance this one has a lower voltage drop.
https://www.mouser.com/ProductDetail/Diodes-Incorporated/SBR30A40CT?qs=7r0W2zb/88wFf/ZYj4zJ8w==

I think you'll want a diode with a screw mount to make it easier to attach to a hunk of metal.
 
Last edited:

Thread Starter

mdr14

Joined Mar 5, 2021
9
I could choose a diode for you at Mouser but I share the concerns of @Papabravo. Be aware that any diode will get hot when significant current flows through it. That means a big heat sink will be required in your case. Do you have room for that?
It is possible that I have room for a heat sink. I won't know if it works until I try it. I would rather try it and fail than not try at all.
 

BobaMosfet

Joined Jul 1, 2009
1,848
Because of the limitations of the circuit board on a 12 volt lithium battery, I need to jumper the negative side of the capacitors directly to the negative terminal. The battery will be in a motorcycle. I need to use a diode, because I want to have a one way out flowing circuit for the ground. When charging, I want the ground charge to go through the circuit board.

I do not know enough about diodes, and there is too much information out there for me to make a determination easily. SO I am seeking some guidance.

The diode should be able to handle at least 25 amps. No or minimal voltage or current drop. The reverse voltage is not that much a factor. A little will be fine.

Thanks for any input.
Hi @mdr14,

Voltage and current do NOT work indepedently of one another. You cannot consider voltage only, you must consider current as well. Current is energy/quantity-of. Voltage is how much force is available to move that energy through the load.

I saw this because a diode always drops a certain amount of voltage in order for it to work at all. Depending on the diode, this can be 0.3V or 2.3 or more volts, depending on the quantity of current and voltage in the circuit. The more current you want to pass, the heavier the diode has to be to handle it.

In order for us to answer your question, at a minimum, you have to give us an idea of voltage in the system (12-14.5V- you've stated), and how much current will be going through the circuit. You also have to clearly explain how the circuit works, not just what you want to share. We are engineer-minds and we look at many more aspects than what you are considering- so we have to know more. What do you mean by "...Because of the limitations of the circuit board on a 12 volt lithium battery,..." - this makes no sense. What limitations do you think are there? Since, by your own admission, you don't really understand electronics all that well, we must (for your safety) question your ability to determine what you think you want to do. And to do that, we need to understand enough about what you are doing, that can approve or caution you, and provide you with useful information.

We're not judging you- we just don't know you. And we don't want to provide bad or dangerous advice. Can you post pictures, sketch any drawing (_anything_ that will give us a better idea of how it's connected now, versus how you want it connected? squares and lines are fine...)

Look forward to helping you, if we can...
 

Audioguru again

Joined Oct 21, 2019
3,516
There is no such thing as a LTO battery. Maybe it is a Li-PO (Lithium-Polymer??
When the diode bypasses the Mosfets then the battery will overcharge and become a bomb.
 

Thread Starter

mdr14

Joined Mar 5, 2021
9
There is no such thing as a LTO battery. Maybe it is a Li-PO (Lithium-Polymer??
When the diode bypasses the Mosfets then the battery will overcharge and become a bomb.
Not these cells.

Additionally, I did say that i needed a diode so that outflow only happened and that charging went through the board.

Lithium Titanate Battery

ithium Titanium Oxide Battery (LTO) is a modified lithium ion battery of voltage 2.4V or 1.9V which uses LTO material as cathode, and LiMn2O4, NiCoMn, LiFePO4 material as anode. Another LTO battery, of which the voltage is 1.5V, it uses LTO material as cathode, metallic lithium or lithium alloy material as anode. LTO battery’s normal working voltage is 2.4V, maximum 3.0V, and working current is more than 2C. Lithium titanate battery has the advantage of more safety, high stability, long life and environmental protecting.
 

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Thread Starter

mdr14

Joined Mar 5, 2021
9
Hi @mdr14,

Voltage and current do NOT work indepedently of one another. You cannot consider voltage only, you must consider current as well. Current is energy/quantity-of. Voltage is how much force is available to move that energy through the load.

I saw this because a diode always drops a certain amount of voltage in order for it to work at all. Depending on the diode, this can be 0.3V or 2.3 or more volts, depending on the quantity of current and voltage in the circuit. The more current you want to pass, the heavier the diode has to be to handle it.

In order for us to answer your question, at a minimum, you have to give us an idea of voltage in the system (12-14.5V- you've stated), and how much current will be going through the circuit. You also have to clearly explain how the circuit works, not just what you want to share. We are engineer-minds and we look at many more aspects than what you are considering- so we have to know more. What do you mean by "...Because of the limitations of the circuit board on a 12 volt lithium battery,..." - this makes no sense. What limitations do you think are there? Since, by your own admission, you don't really understand electronics all that well, we must (for your safety) question your ability to determine what you think you want to do. And to do that, we need to understand enough about what you are doing, that can approve or caution you, and provide you with useful information.

We're not judging you- we just don't know you. And we don't want to provide bad or dangerous advice. Can you post pictures, sketch any drawing (_anything_ that will give us a better idea of how it's connected now, versus how you want it connected? squares and lines are fine...)

Look forward to helping you, if we can...
Some of the stuff may be covered in an NDA. So I have to be careful what is revealed.
 
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