Inrush limiter For Series Parallel 36v setup

[Thunk303]

Hey Team.

I am sure this has been solved but I can't for the life of me find the thread so...

I have 4 x 18v Makita batteries in series Parralel into a cheap controller and a 36v 800w brushed DC motor.

https://www.motiondynamics.com.au/dayton-800w-1hp-36v-dc-planetary-gear-motor-500-rpm.html

Firstly, it works a treat, now I would like to backtrack and add as much safety to the gear and myself as possible.

I have a 20amp fuse on each battery but I would like to add inrush limiters to avoid the spark I get when I connect the last batteries and hopefully protect all parts of the circuit.

As I understand it so far, which is not much, PTC MOV's would do the trick but I am unclear what value devices I need and dont trust my feeble calculations from online examples...

Any input appreciated or other better ideas welcome.

Cheers and happy travels.
Dean

 

[fechter]

Normally, the spark happens when the battery is connected to the controller. The capacitors in the controller are at zero volts and you suddenly apply pack voltage and get a big spark. There are several ways to avoid this, but it will be a challenge when using tool packs. I would suggest placing a hefty switch between the controller and batteries and switch it off when installing the batteries, then turn it on. Place a resistor (like 100 ohms) across the switch. This limits the current during precharge and stops the spark. If you use a big solar circuit breaker for you switch, you may not even need the resistor (but I would still recommend it).

There is a circuit that can automatically do the precharge instead of a switch, but it's complicated.

 

[E-HP]

I have a 20amp fuse on each battery but I would like to add inrush limiters to avoid the spark I get when I connect the last batteries and hopefully protect all parts of the circuit.

Any input appreciated or other better ideas welcome.

I currently use a pushbutton and resistor as an antispark circuit, but before that I used a 40A AC breaker as a switch for a few years. I did an autopsy of the breaker contacts after thousands of actuations, and the contacts were in great shape with no pitting, etc. It's functioning solely as a switch, since an AC breaker will not trip under DC load (the max it was subject to was 110A).
https://endless-sphere.com/forums/viewtopic.php?f=3&t=117505&p=1730266&hilit=autopsy#p1730266

The resistor circuit is a more elegant solution, but I wish I would have kept it simple, and my switch back.

 

[amberwolf]

since an AC breaker will not trip under DC load

Oh, it will still trip (assuming it's undamaged), once the current exceeds it's limit by enough for long enough***, but it may not be able to stop the arc across the contacts as it opens, so a fire could occur in this event if the current continued at a high enough rate to keep the arc going, and the breaker materials were vulnerable to fire from inside the breaker or materials around the breaker heated enough from it.

Alternately if the gap is small enough between the contacts, the arc might instead weld the contacts together and prevent the breaker from ever tripping again. (though this happens much more often to switches and relays/contactors (or breakers) being closed than opening/tripping).


*** see the breaker manufacturer's spec sheet for the current vs trip vs time curve; if the overload is relatively small it can take a surprisingly long time to trip the breaker.

 

[Thunk303]

Greatly appreciated all, I'll have a look around local suppliers and report back

Dean

 

[Matt Gruber]

the weak point is the brushed dc motor. if the controller ever shorts it will send you flying off, maybe to the ER.
so on my scooters i use an 80 amp relay with a left thumb momentary on push button. so if the controller shorts, my thumb gets jolted off the switch, and the relay cuts the power .
and of course that switch does nothing until i turn on the on/off switch which also has the precharge resistor.

 

[E-HP]

Oh, it will still trip (assuming it's undamaged), once the current exceeds it's limit by enough for long enough***, but it may not be able to stop the arc across the contacts as it opens, so a fire could occur in this event if the current continued at a high enough rate to keep the arc going, and the breaker materials were vulnerable to fire from inside the breaker or materials around the breaker heated enough from it.

*** see the breaker manufacturer's spec sheet for the current vs trip vs time curve; if the overload is relatively small it can take a surprisingly long time to trip the breaker.

You are absolutely correct. Not sure where I got my wires crossed, and maybe lucky to never had the old breaker trip, even though I know I had subject it to a lot more current than it's rating for fairly long periods (I think I read an article about how the magnetic tripping of the thermal magnetic breaker may work differently between AC and DC, but makes sense that the thermal tripping would still occur whether AC or DC). Since I have to replace the AC/DC breaker that I'm using now, since it does trip at 50A continuous, maybe I'll just go with a normal toggle switch. I don't want anything tripping under load except the BMS.

 

[socrace]

You are absolutely correct. Not sure where I got my wires crossed, and maybe lucky to never had the old breaker trip, even though I know I had subject it to a lot more current than it's rating for fairly long periods (I think I read an article about how the magnetic tripping of the thermal magnetic breaker may work differently between AC and DC, but makes sense that the thermal tripping would still occur whether AC or DC). Since I have to replace the AC/DC breaker that I'm using now, since it does trip at 50A continuous, maybe I'll just go with a normal toggle switch. I don't want anything tripping under load except the BMS.

 

[fechter]

I agree that is a good point. I had a controller short on my original Zappy scooter that resulted in a serious injury. I had a relay and handlebar mounted switch, but it happened so fast I couldn't hit the switch. Golf carts with brushed motors usually have the contactor switch built into the throttle so when you let off the throttle, it automatically disconnects the motor, but that's a little different setup.

 

[Thunk303]

the weak point is the brushed dc motor. if the controller ever shorts it will send you flying off, maybe to the ER.
so on my scooters i use an 80 amp relay with a left thumb momentary on push button. so if the controller shorts, my thumb gets jolted off the switch, and the relay cuts the power .
and of course that switch does nothing until i turn on the on/off switch which also has the precharge resistor.

Very interesting.

Does anybody have a rough circuit diagram or link/reference on what to purchase and how to wire this up?

Is there better controllers that short open at failure?

I currently have the hydraulic brake lever on the left handle bar, not sure if my 6yo can hold a button and pull the brakes at the same time...

 

[Thunk303]

Battery Switch Power Cut On/Off Master Disconnect Isolator Car Vehicle RV Boat | eBay

Battery disconnect switch can disconnect the battery safely to eliminate any power draw from the battery when vehicle or boat is not in use. Widely used for Car, Marine, Boat, RV, Camper, Travel Trailer, Truck, ATV, UTV, Battery banks and other 0-60V Device.

www.ebay.com.au

I found this switch which is small enough to fit in the space I have available.

Regarding the 100 Ohm precharge resistor, what wattage rating would be appropriate?

Cheers

 

[Thunk303]

As a reference I have started another thread giving a basic run down of the build and parts used, although I am not sure I have posted it in the right section?

Happy to move but not sure how or where too..

36v Makita kids Trike

Hey Team. Just a thread to leave a few breadcrumbs for other parents silly enough to build their child an electric trike/buggy. I'll try and keep it short and sweet. First a few links. Motor: You will need the gear reduction, there is no two sprocket combination that will give you any...

endless-sphere.com

 

[ichiban]

Does anyone experience these DC breakers tripping from vibration/shocks during rides ? These solar DC breaker are designed for stationery usages and we just lend them for our e-bike app. Doubt it if e-bike vibration/shakes will unexpectedly tripping of the breakers. It can be very dangerous, especially during critical passing slow trucks. My intended on-hand cheap 32-Amp solar cct breaker looks like this, of course detail spec is hard to find :





I tend to go for breaker rather than fuse due to its dual functions : over-current protection and as a switch.

Or should I go for the RV type cct breakers below instead ? This one is turning type to power ON/OFF that should be better for vibration. But the size is a bit bulky for e-bike. Plus I need to waterproof any of these breakers I chose since rainy season is coming in my area.





Thanks for any comments.

 

[fechter]

The Sur-ron uses a 100A version of a solar breaker. They can handle a lot of vibration and don't trip for brief overloads. I don't recall any reports of them failing. They are also designed for higher voltages and will survive a trip. The ones made for 12v could arc when they trip and start burning. It depends on how far the contacts open when they trip or if they have something to prevent arcing.

 

[amberwolf]

I have a similar designed rail-mount breaker on SB Cruiser (and used the same kind on my old CrazyBike2), used for years, and they never tripped from vibration or shock, even when I have broken rims on potholes that yanked me to a stop.

They are not waterproof or resistant in any way, however, so I recommend isntalling them inside something that is.

The RV stuff may not be rated for a high enough voltage; you'd have to check.

Whatever you use needs to be rated for *at least* the voltage it will have across it when open. If it is not, it may not be able to break the arc when it pops under load, and then you have an arc-welder running inside your breaker, destroying it and possibly setting fire to the breaker and enclosure it's in, *and* nothing is protecting your wiring/etc since it's still passing current it should have stopped at this point.

They also need to be rated for DC, if they are only rated for AC they may have the same problem as above *even if they are rated for a high enough voltage* because DC does not have a zero-crossing point and the breaker may depend on that.

Specs on the rail breakers shoudl be easy to get from the manufacturer's website. Such as these AC-only breakers:

M9F22245 - Miniature circuit breaker (MCB), Multi9 C60SP, 2P, 45A, C curve, 5kA (UL1077), 10kA (IEC/EN 60947-2) | Schneider Electric Global

Schneider Electric Global. M9F22245 - Miniature circuit breaker (MCB), Multi9 C60SP, 2P, 45A, C curve, 5kA (UL1077), 10kA (IEC/EN 60947-2).

www.se.com

https://www.se.com/ww/en/product/download-pdf/M9F22245

If you have the model number on a specific breaker you already have (or are getting) you can search for just that model number on google and probably find the manufacturer data for it.

 

[ichiban]

Thank you guys. These details are very useful for our e-bike DIY and cannot be found easily anywhere unless asked from the gurus here on ES. You guys are really knowledgeable on the subject.

My DC breaker use case is for powering/protecting a 20S3P of Samsung 40T cells (4A, max 35A per cell) to be coupled with Grin's 8T motor via PR3 & CA3 build - too long overdued.

The 32-A "Applegreen" DC breaker in question should be a Chinese clone and exact model spec is not easy to find. So, I will have to find some comparable type/size spec of other famous brands and go from there. But I am pretty sure, after reading your comments, that it should be very OK to use this DC breaker for my build.

 

[fechter]

That should work great.