Eastwood’s first battery build

[Eastwood]

If you have a programmable BMS, it may be able to balance at lower voltages, to allow for the specific situation you want to use. There will then be setpoints for this in the setup software.

Do you have any recommendations for a BMS? With the amount of current I’ll be able to pull from this pack, I plan to bypass the discharge but will definitely be using the BMS for charging.

As far as the discharge wires I plan to go with 0000 AWG or I think they call it 4/0 AWG wire.
Going to be some heavy wire
Somthing like this,
4/0 AWG Marine Wire - Tinned Copper https://a.co/d/7V7RiZN

Not sure yet what type of connectors I will use, but I need something huge if I end up going with the 0000 AWG.

Also...if you use well-matched cells to start with, where all the cells have identical properties (internal resistance, capacity, etc), you won't need to balance them until they age enough to no longer be identical.

Ahhh makes sense, I’m learning

 

[Eastwood]

Does anyone have recommendations for a battery disconnect. Thinking something that can handle close to 1000amps, just so there’s no added resistance. Plan to put the battery disconnect, lever/switch where the gas cap used to be to have easy access and for safety.

Something like this, but better quality

 

[harrisonpatm]

Also...if you use well-matched cells to start with, where all the cells have identical properties (internal resistance, capacity, etc), you won't need to balance them until they age enough to no longer be identical.

In fact, I would recommend turning balance off once they're balanced and built. Cells coming out of balance is a symptom of a problem, and if a balance BMS is covering that symptom by continuously attempting to balance cells, you are less likely to see problems when they arise. You could turn it on twice a year or something to rebalance cells, then turn it off again.

Does anyone have recommendations for a battery disconnect. Thinking something that can handle close to 1000amps, just so there’s no added resistance. Plan to put the battery disconnect, lever/switch where the gas cap used to be to have easy access and for safety.

You mentioned in an earlier posthat you were going to need a contactor. Isn't your contactor going to be your disconnect? The ones on batteryhookup.com are rated for 900amps. (Edit, just checked, they're rated for 500amps, not 900: TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v)

You can have both a coil-driven contactor as well as a manual disconnect, it's not inherently bad, just wondering if it's necessary. And if you don't need the manual disconnect, you can save the gas cap for the charging port, like all the cool kids do!

 

[999zip999]

I think a pre-charge resistor from the battery to controller before you hook up the main wires. I'm throwing this out there to hear other people's opinion on how to best way to connect battery to controller.

 

[Eastwood]

In fact, I would recommend turning balance off once they're balanced and built. Cells coming out of balance is a symptom of a problem, and if a balance BMS is covering that symptom by continuously attempting to balance cells, you are less likely to see problems when they arise. You could turn it on twice a year or something to rebalance cells, then turn it off again.

This makes perfect sense because if I had the BMS always balancing, I wouldn’t know if any cells were actually dropping in voltage. It’s almost like the BMS would be hiding this issue by constantly balancing

You mentioned in an earlier posthat you were going to need a contactor. Isn't your contactor going to be your disconnect? The ones on batteryhookup.com are rated for 900amps. (Edit, just checked, they're rated for 500amps, not 900: TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v)

You can have both a coil-driven contactor as well as a manual disconnect, it's not inherently bad, just wondering if it's necessary. And if you don't need the manual disconnect, you can save the gas cap for the charging port, like all the cool kids do!

So basically, I don’t need any type of manual disconnect if I’m using a coil contactor?

So the discharge wires coming from the BMS could directly bolt to a coil contactor…Then the discharge wires coming from the coil contactor, could directly bolt to the controller, without using any type of connector between? Pic/diagram below for the question

I think a pre-charge resistor from the battery to controller before you hook up the main wires. I'm throwing this out there to hear other people's opinion on how to best way to connect battery to controller.

I was wondering this as well

 

[harrisonpatm]

So the discharge wires coming from the BMS could directly bolt to a coil contactor…Then the discharge wires coming from the coil contactor, could directly bolt to the controller, without using any type of connector between? Pic/diagram below for the question

Answer is yes, but your diagram is wrong, I'll explain. Yes, in that you need a way to disconnect the battery from the controller, and a contactor is one way of doing that. A big ol high-current switch, like what you linked, can also do that if you want, people like using a contactor because you can trigger the coil with a small switch, like a little toggle or rocker, on your handlebars. Or a key switch.

There's not really a good reason to have both a contactor and a manual cutoff switch. Not to say there's no reason, I just can't think of a good one.

Your diagram is wrong because the contactor has two main terminals, and it's interrupting one line from the battery to the controller, either the positive or negative. You drew it trying to connect to both poles, you just need it on one. If you connected your battery like that, not only would there be no way of disconnecting the controller, but once you do flip the contactor, you dead short the battery.

Standard practice is that the BMS and shunts are on the negative battery pole, while contactors, switches and fuses are on the positive. Google a wiring diagram for your controller, you'll see a few different examples. Or just use the search function on ES for wiring diagrams, and you'll find dozens of examples, from which you can cherry pick what works best for you.

Use the ES search option for precharge suggestions, more than one way to do that as well, you'll need to calculate what size resistor you need, if you want manual control of it, ect.

 

[amberwolf]

If you really need a manual disconnect (such as an antitheft measure, or fire-safety shutoff, etc) you could just use another of the same kind of connector you end up using for the battery connector in the first place (if you don't just bolt it directly in).

This second connector has one of it's shells mounted to the frame. The ohter shell gets a T-handle, and not connected to the frame. The frame mounted shell only gets the main positive cable wired to it, no negative. One contact of the FMS gets the main positive output from the battery, the other gets the main positive input to the contactor (assuming that's on the positive side like usual). The non-mounted shell just gets a loop of wire from one contact to the ohter. When you have it plugged in, it completes the circuit. When not, the system can't operate because it's missing the battery positive.

For myself, I'd use Anderson SB series for this, since they are made in many sizes, and genuine ones are good quality and will last a very long time even if you frequently cycle the connections (which you won't, for this, most likely--I don't cycle mine much but mine also all came used off of other equipment where I don't know their previous cycle life/usage). They come in two contact retention force options AFAICR, so the one for the battery you use the high-RF version so it can't come unplugged easily, and the disconnect one you use the low-RF version so you can more easily unplug it if you have to (becuase at the size you'd probably use, they get pretty hard to unplug). The shells are the same either way. You can also get keyed / color-coded shells, so different things using them cannot be connected incorrectly. They also make T-handles (and panel mounts, etc) which makes the whole disconnect-thing easy. Example pic found in google search:


Main two disadvantages to Andersons are cost and size--each shell will probably be about the size of a small pack of cigarettes, for a couple hundred amps version. (I use the SB50s, which are a quarter that size, and good for over 100A, but AFAICR they won't fit 0000 size wiring in the contacts (which are the same as those in the PP75), so you'd need the next size up at least--I think 6gauge is the biggest the SB50/PP75 contacts will take. I think the SB120 will take up to 1gauge).

The other disadvantage in some setups due to constrained space or routing limitations is the contacts must be able to "float" in the shell, so they can self-align during mating. If they can't, you can end up with only edge-contact, and a high-resistance connection that heats up and can even melt the shell, or start a fire. So you can't use wire with insulation so thick it fills the shell hole, and you can't route wires such taht they pull tangentially to the shell exit forcing the contact to twist or angle when connected. This is what usually gives Andersons a bad rep (besides the non-genuine ones having softer shells and weaker springs that allow this to happen even more easily), but is easily avoidable by simply routing and securing wires correctly.

 

[Eastwood]

people like using a contactor because you can trigger the coil with a small switch

Ok nice, that sound like the plan!
Also the coil contactor will act as my overcurrent protection as well, right? Since I’m not discharging through the BMS, this would act as overcurrent protection if I’m understanding this right?

Now I need to find a coil contactor that can handle roughly 1000 amps.

Use the ES search option for precharge suggestions, more than one way to do that as well, you'll need to calculate what size resistor you need, if you want manual control of it, ect.

Is the resistor necessary since I’m using a coil contactor? I’m guessing if I didn’t use a resistor, would get a spark inside the contactor once it closes the circuit, right?


I definitely like the price of that coil contactor you posted, but I don’t think that will work considering my controller can output 850 phase amps.

If you really need a manual disconnect (such as an antitheft measure, or fire-safety shutoff, etc) you could just use another of the same kind of connector you end up using for the battery connector in the first place (if you don't just bolt it directly in).

Yeah, think I will go the route of not using connectors and just bolt directly. Seems like the connectors aren’t necessary since I’ll be using a coil contactor and have the ability to open the circuit.

I guess I’m still trying to understand whether I need a resistor or not if I’m using the coil contactor?

 

[Eastwood]

Found this contactor. Same brand but higher current rating.

EVC500 AAANAM 2299223-2 Contactor Relay 12V 1000A For New Energy Vehicles | eBay

Find many great new & used options and get the best deals for EVC500 AAANAM 2299223-2 Contactor Relay 12V 1000A For New Energy Vehicles at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[harrisonpatm]

Also the coil contactor will act as my overcurrent protection as well, right?

Nope, the contactor has no sort of overcurrent protection. It's not different than a switch, and all switches have a current rating, which, if you exceed it, will melt the contacts.

For overcurrent protection, since you're planning on bypassing the BMS for discharge, you'll want to alter the parameters of your motor controller to limit or cap max battery current.

Is the resistor necessary since I’m using a coil contactor? I’m guessing if I didn’t use a resistor, would get a spark inside the contactor once it closes the circuit, right?

The resistor is still necessary. The contactor can handle a spark, at least the ones you suggested so far. What the resistor is for, is making sure that when the battery connects to the controller, there isn't a surge current to flood the controller's capacitors too quickly, causing excessing wear.

A coil contactor is a switch like any other, except instead of using your thumb to flip a switch, a solenoid coil is being used to close the circuit.

go to 2:18 to visualize what's happening inside your contactor

I definitely like the price of that coil contactor you posted, but I don’t think that will work considering my controller can output 850 phase amps.

The contactor is placed on the positive line between the battery and the controller. It needs to be rated for battery amps. Which, I'm guessing, will be more in the range of 200-400, given the info you've provided so far. The amount of current going from the battery to the controller.

Phase amps are what the controller outputs to the motor, via the three large phase wires. No switch or contactor. Phase amps can indeed reach 850 or so in a setup like this, but they are AC current, so they don't require as thick of wires as the ones from the battery to the controller.

 

[Eastwood]

Nope, the contactor has no sort of overcurrent protection. It's not different than a switch, and all switches have a current rating, which, if you exceed it, will melt the contacts.

OK gotcha! I was thinking if it exceeded, let’s say the 500 amp rating of the contactor, it would trip, but I get what you mean now, that’s just the rating it can handle, and if you go beyond that, it could melt the contacts.

For overcurrent protection, since you're planning on bypassing the BMS for discharge, you'll want to alter the parameters of your motor controller to limit or cap max battery current.

Could consider using a breaker instead of the contactor to have overcurrent protection, in the case the controller limit settings failed or something.

The resistor is still necessary. The contactor can handle a spark, at least the ones you suggested so far. What the resistor is for, is making sure that when the battery connects to the controller, there isn't a surge current to flood the controller's capacitors too quickly, causing excessing wear.

Ok makes sense. The resistors I’ve used in the past came pre-installed in the connectors, XT 90’s.
With this build, I don’t want to use those connectors with the amount of current so I’ll do the set up like you’re suggesting and figure out what type of resistor I need.

The contactor is placed on the positive line between the battery and the controller. It needs to be rated for battery amps. Which, I'm guessing, will be more in the range of 200-400, given the info you've provided so far. The amount of current going from the battery to the controller.

Phase amps are what the controller outputs to the motor, via the three large phase wires. No switch or contactor. Phase amps can indeed reach 850 or so in a setup like this, but they are AC current, so they don't require as thick of wires as the ones from the battery to the controller.

Ok, from my understanding, I knew the phase amps came from the controller like you’re suggesting, but was thinking the battery still had to produce the phase amps for a short burst. So that means it’s strictly the controller producing that large amount of phase amps for short burst like acceleration from a stop or going up a steep hill climb etc.

Here’s the controller, ND72850

https://a.aliexpress.com/_mM2cfuu

450 dc amps
850 phase amps

 

[harrisonpatm]

Here’s the controller, ND72850
https://a.aliexpress.com/_mM2cfuu 450 dc amps
850 phase amps

The battery does indeed increase current for short bursts, but the phase amps increase exponentially in relation to that. So ignore phase amps for now. This controller can handle a maximum of 450 battery amps. Meaning your contactor needs to be rated for that, so the first one I linked will be fine at 500a rating. Also, its very likely that you'll only be seeing 200-300 battery amps max, given the rest of your build.

Could consider using a breaker instead of the contactor to have overcurrent protection, in the case the controller limit settings failed or something.

Yep, place this on the positive line between the controller and the contactor. And purchase something that will cutoff before your weakest link's maximum. It's going to be either your battery or your controller, and you need to decide where you're going to limit it. For example, your controller is rated for 450 amps. But do you want to give it 450 amps all the time? probably not. So maybe a 350-400 amp breaker. But now, you need to be sure that you battery has zero problem delivering 350-450 amps.

I believe you decided to go with 20s17p. So 17p Molicel p42 cells, max discharge rating 45a. That's max, probably with a lot of voltage drop. So assume 30a max for better cell life. Times 17p, means your battery should be fine with 500ish amps. Meaning your controller is the weak link, that's what you need to size the breaker for. Still you should be using programmable current limiting in the controller, but you're right, you'll want a fuse on the controller in case that fails.

How's the battery testing going?

 

[Eastwood]

its very likely that you'll only be seeing 200-300 battery amps max, given the rest of your build.

Why do you say, “I’ll only be seeing 200-300 battery amps max”? because that’s what I would have the controller set to?

If that’s what you mean, yes more than likely I’ll have the DC amps set to around 225-ish amps. I don’t plan on using 450 A, unless I’m racing for a short period against buddies with their gas bikes. Or just messing around for short periods, doing some acceleration runs. I plan to keep the DC amps as low as possible will with still having great performance, while the main goal is range for Enduro and trail riding.

But do you want to give it 450 amps all the time? probably not

Naw, but it will be fun to use 450 amps every once in a while

How's the battery testing going?

Not yet, my friend. It’ll be about a month before I can order the cells. Still wrapping up the actual bike build, Almost done! Plan to order the controller soon and get that mounted first before purchasing the cells. Financially, I’ve had to do this build piece by piece not all at once

Thank you very much for all your help!!

 

[harrisonpatm]

Why do you say, “I’ll only be seeing 200-300 battery amps max

Educated guess based on what I've seen so far, and reports from other peoples' builds. Your frame isn't terribly heavy, you're using energy-dense li-ion cells rather than LFP, you mentioned a top speed goal of 50mph... I'm guessing that you'll be seeing 25-100 battery amps for normal acceleration and cruising, 150amps when you need to take off from a standstill, 200 when you're going uphill, 300-350 in bursts when you're going up a really steep hill fast.

Don't change anything though. If you plan your cabling, connectors, battery current, battery build, ect., for 450 amps, and you only give it 150 regularly, that just means you'll be gentle on your batteries and your cables will offer negligent resistance.

 

[Eastwood]

Don't change anything though. If you plan your cabling, connectors, battery current, battery build, ect., for 450 amps, and you only give it 150 regularly, that just means you'll be gentle on your batteries and your cables will offer negligent resistance.

Yeah exactly!
Plan to use the biggest AWG wires, etc. etc., to give the least amount of resistance as possible. Plus, I’ll keep the battery cables as short as possible, same with the phase wires. I’ll be crimping, the lug connectors going to the Contactor and controller, no soldering. I need to get a good crimping tool to do so tho.

 

[gobi]

Eastwood,

1. In-rush
I found this cool solution on the diysolarforum but I think I have seen it here to.
You get a marine battery switch for 2 banks.
You have a switch which goes 0, 1 or 2
0 = off
1 = connection to battery with an INLINE 100W resistor (or more if you need, do the calc)
2 = connection to battery

I will post a pic and/or the thread when I find it again.

Gobi

 

[gobi]

Found it

 

[Eastwood]

Found it

Thanks for posting, I’ll look into this
I still need to do my homework on figuring out how to calculate for the resistor. I haven’t dug into this too much as there’s many other things with this build that needs to get completed first.

 

[Eastwood]

So I would like to find a BMS that could handle 450 continuous amps but it seems nearly impossible to find. Does anyone have suggestions on a BMS that can handle 450amps continuous discharge??

It seems like most people just bypass the BMS for high discharge situation, which has been my plan from the beginning, but would definitely rather have the discharge ran through the BMS if possible.

I found this ant BMS 500amps, but The continuous discharge is only 240amps.
ANT smart BMS

 

[amberwolf]

There's a few threads about precharge where various calculations are shown. I forget whose thread it was, but in the last few months I went thru it with someone for a few scenarios about contactors, precharge, etc.


For a high current BMS, get one that uses a contactor. Then you use it to drive the contactor you are already intending to use (just make sure the BMS can control the voltage/current the contactor coil operates at, or get a contactor with a coil of the appropriate voltage/current), and you are not relying on someone's bad FET gate drive design or voltage spike protection to keep your BMS operating. (you can DIY one, instead, but using one meant to drive a contactor is probably simpler).

There's some threads showing contactor-based BMSs, but I don't have any links ATM. These are two searches that show some relevant info (a lot of it isn't, today, though normally there is a lot more).

Google Search

Google Search

 

[harrisonpatm]

BMS-controlled contactor for high-amp discharge

I thought I'd start a new thread split off from this one to discuss DIY BMS contactors at length. Planning stages for my next build. I'd like to use the salvage contactors I got from Battery Hookup for this one (https://batteryhookup.com/products/te-connectivity-ev200aaana-500a-0-900vdc)...

endless-sphere.com

It was my thread actually, and you've reminded me that I was meaning to sketch out a basic diagram for DIYing it without having to purchase a pre-made contactor-based BMS. I just posted on that thread with a quick sketch of what to shoot for.

 

[Eastwood]

What do you guys think about something like this? I should’ve showed in the diagram, I’m bypassing the BMS for the discharge, so, just ignore the wires coming from the BMS.

 

[Eastwood]

If this circuit is correct,
Could use 2 switches on the handlebars or install somewhere on the gas tank. Probably easier to mount somewhere on the bike like the gas tank instead of running wires all the way up to the handlebars.

So if I’m understanding this right, I would activate the relay so the current can flow through the resistor to pre-charge the capacitors in the controller. After that, I would close the circuit through the coil connector and be connected to the load/controller.

So my question is, would I need to turn off the relay that Controls the pre-charge before closing the circuit through the coil contactor?

I could use a switch similar like gobi suggested.

 

[j bjork]

You can use a low current bms and bypass it on discharge, but let it control the "on" wire on the controller and the dc-dc converter for the contactor. That way you still have LVC and protection if a single cell group goes low (or high). With a higer current bms you can move the shunt so it senses the current even though it is bypassed, like I do on the yamaha. Then it can still cut on overcurrent and show relevant currents and SOC.

 

[gobi]

Op,

I like how the EG4 batteries are setup,
I will post a link to Will P taking one apart.

High level:

Cells > Seplos bms with inrush circuit > circuit breaker > fire arrestor (not sure where this is, maybe someone can help us confirm) > connector > controller

The Seplos BMS is bit big but hey you gots the real state

Side topic: I would steer you away from 21700s and to factory packages EV units that you can repurpose. But on the flip side, similar cells in other bikes like Surron et al is working fine.