Noob installing kelly controller, whats a precharge circuit?

I recently blew out the stock chinese controller in my scooter and have decided to replace it with this kelly KEB controller, but I'm having some trouble understanding the "precharge circuit".

Here's the diagram in the manual:



My previous controller didn't have anything like this. The key switch went straight to the PwrOn wire on the controller, without all this convoluted relay system. However, reading up on it, it seems this is necessary for like charging up the capacitors in the controller or whatnot, and without it these controllers are known to burn out.

So, I've got a couple questions.. They don't mention anything about what sort of value you ought to use for this "main contactor". In fact it's never mentioned anywhere in the manual. Am I to assume I need to find a relay that can switch the full load of my bike? 66V, 60A? That seems like a lot for most relays. Do I need to find an automotive solenoid or something? Also, it looks like the coil needs to take battery voltage? All the relays I've ever seen have taken 12-24v for the coil.

Then, if I'm not mistaken, this 10W resistor is going across B+ and B- at all times, even when the bike is switched off? Isn't that A: going to waste ten watts for no goddamn reason, draining my battery? and B: going to get very hot, and I'll need to heatsink this resistor?

Following this line of reasoning, I got to wondering if I should put in a switch to switch on the precharge circuit, then, what if I put in a relay to switch on the precharge circuit when I switch on the bike, leading to an infinite loop of relays and me questioning my sanity as well as the need for a precharge circuit in the first place.

Help!

All good questions and thinking here. Have you tried searching the forum on the subject yet? There are a few ways to go about doing this. Not terribly complicated once you get your hands around a couple basics. You're on the right track though.....

I have actually tried searching for info on this before posting. Using both the forum search feature as well as google. Unfortunately, it seems a lot of people use the word "precharge" in threads where no one actually explains what a precharge circuit is, why it is needed, what kind of parts are needed, why those values of parts are needed, what kind of caveats there are, etc. I mostly found a lot of threads mentioning the circuit off-hand, or kelly controller diagnostic help threads where people were asking about a precharge circuit while trying to diagnose their problem.

If you can link me to a specific thread or wiki page that explains this stuff, I'm happy to read up on it and learn on my own.

However, I've found none of that, which is why I'm asking.

Cheers!

I don't know a good link, so....

You need this because if you just close the contactor with no series resistance, there will be a large spike of inrush current as the highly capacitive load circuitry is connected to battery power. This can actually weld your contactor shut or pit it up with arcing. If you bring that capacitive load up to battery voltage slowly through a current-limiting resistor before directly connecting to the battery, you avoid this problem. You already pretty much get this, it seems.

The system diagram you have is confusing/not well conceived. As you point out, precharge is ALWAYS connected to the load, so this is an unnecessary parasitic load on the battery when parked. I like the setup I have in my motorcycle, where the key turns on the 12 Volt system, and also connects the 48V drive battery to the precharge resistor, which is connected directly to the motor controller power input. There is a toggle switch that is used to turn on the contactor and motor cooling fan a second or so after key on. You'll probably want to use some variation on this theme. It's not too hard to find golf cart wiring diagrams on the web to see something similar.

Resistor Ohms value can be almost anything greater than a couple of Ohms. Higher voltages generally dictate higher resistance values, but keep in mind the Chevy Spark has a 350 Volt pack and uses a 25 Ohm precharge resistor. What makes it expensive is that the resistor is encased in ceramic in an extruded aluminum heatsink, and is rated for (I think) 150 Watts. Higher resistance values mean slower rise time, which means you need to wait longer to turn your contactor on. Lower resistance means faster rise time and thus a shorter wait to flip on the main contactor switch. To get that though, you need a fairly beefy resistor (150 W is overkill, even for the car really) to handle the power. You can use hundreds or k's of Ohms of resistance in a 5 or 10W resistor, but you'll have to live with the slow rise time. Remember that in practice, power should be flowing through the precharge resistor for fairly short periods of time (seconds) so you don't have to go nuts on the power capability or heat sinking. I would think a 50W Ohmite aluminum-cased resistor in 10 or 20 Ohms with a modest heatsink would be a nice performer for most applications. The units I'm thinking of are gold in color, popular for use as dummy loads and are reasonably priced.

About the contactor...yes, this is not an ordinary relay. There are lots of options out there. They can get pretty pricey. I can set you up with some nice contactors that are rated for 100 Amps if you need any. They have 12 Volt coils, as do most. (Is that supposed to be a 12 or 24 Volt battery in the diagram?) PM me if you're interested.

Hope that helps.

Do you have a voltage readout on the bike that only displays when the controller is connected to power?

Easy way is to setup on the positive main battery cable some sort of disconnect, either a contactor(essentially a big switch usually controller by 12V power) a normal switch or just a simple plug. On either side of the plug have a short section of cable ~16awg would be good. Have it so that you can connect them together just before the main battery connection is made. The idea is to use a resister that allows the controller to fill up its main power capacitors over a few seconds rather then instantly. I generally use 370ohm-500ohm 10W resistors, i find the 1000ohm that Kelly uses is too slow and if you have anything like a cycle analyst in the circuit it does not charge up at all. If you have a voltage monitor you can read this value as it should slowly go up from 0- just under your pack voltage. When it gets to within 10V of your pack voltage you connect the main power cable between the controller and the battery. Once that is done i recomend disconnecting the precharge cable as it is not needed and will just get hot.

The resistors are like a $ each so cheap enough that you can by a few if needed. If you have a voltage monitor and it never gets close to the pack voltage(should only take ~2-5 seconds) then change the value to a different one. I think i have a 150V bike using ~180ohms and a 84V bike is running around 370ohms. But then they have different controllers and different bits that turn on with the controllers draining power.

Basic pic to give you a idea


Or you can buy this http://www.zeva.com.au/index.php?product=110 If you have a 12V supply and a contactor. Makes turning the bike on a simple turn of a key switch. It does everything for you

Bluefang said:

Once that is done i recomend disconnecting the precharge cable as it is not needed and will just get hot.

Click to expand...

No it won't. With the contactor closed, there is a dead short between the battery and controller, and thus also across the resistor. Virtually zero current will flow through the precharge resistor once the main contactor is closed. The only reason to disconnect the precharge resistor after closure of the contactor is to protect the resistor and it's harnessing in the event of a system failure that results in precharge being left on as the sole power connection for an extended period of time. Even this is unlikely to be a serious problem...current in most systems sitting idle is very low. The resistor should only be able to overheat if you try to run the vehicle drive power through it, and you'll notice this as a problem very quickly because the vehicle will barely move in this state, if at all.

Thank you! This is all incredibly helpful.

The controller did come with a resistor. It's a cheapo ceramic potted wirewound thing labeled RX21. It's 1kohm, so how long would you suppose it would take to precharge? Seconds? Fractions of seconds? I'm tempted to use another relay to turn on the main contactor, just to eliminate the need for another toggle switch. There's also a setting in the controller you can program a startup delay, but I suppose that has nothing to do with the charging of the caps and I still need a precharge circuit regardless.

wb9k said:

the setup I have in my motorcycle, where the key turns on the 12 Volt system, and also connects the 48V drive battery to the precharge resistor

Click to expand...

This is brilliant. I never really thought to use the 12v system to switch on the main system, but there's no reason that wouldn't work. Mind you, it adds a point of failure where if my dc-dc fails I can't start the bike, but whatever.

The diagram shows the relay coil using the battery voltage. In my case, 60V. Hadn't occurred to me I have a source of 12v laying around.

How much would you want for one of those contactors? If I'm not mistaken, cars have a 12v solenoid that switches hundreds of amps to the starter motor, and I have some car friends who probably have one laying around. I could probably use one of those, no?

Thanks again!

Strictly speaking there is no reason to use a contactor there. You could eliminate the diode, contactor, and primary fuse and replace them with a circuit breaker.

An 80A 150V unit (Midnight Solar MNEDC80) would do the job for about $20.

The breaker can be left ON all the time if you wish so it can be under the seat, etc.

As mentioned above, their circuit leaves the controller connected and potentially drawing a very small current through the pre-charge resistor as long as the battery is connected (not sure if the controller has an internal bleed-down resistor on the caps). If you want to store the bike, disconnect the battery.

The circuit breaker idea is a good one too. This is the arrangement on my Rose scooter, I think. Telektik makes a good point that the power ultimately dissipated through a precharge resistor left connected all the time will be tiny--in a system without design errors that make this statement false. Most motor controllers draw a tiny amount of quiescent standby current--the resistor only sees big power during inrush. Still, I don't like the idea of parasitic loads on a battery when not in use, and if you've got something else powered on there through error or poor design, your risks can add up quickly.

If you (or anyone else) needs medium to heavy duty contactors, PM me. I have several around and will make them available cheap but I don't want to start throwing numbers around in this thread. Other affordable options have been suggested here as well. Do what works for you.

If you want to eliminate any small draw from the 'always safe' precharge configuration recommended by Kelly, you might use this circuit.
Here the keyswitch replaces the usual separate precharge button, so you must remember to turn on the keyswitch BEFORE you turn on the breaker. Here we are assuming you will switch on the breaker once in a blue moon, and just leave it ON. Turning off the breaker completely disconnects the battery for long term storage.

I would probably use a 470ohm resistor myself to speed things up.

resistor when connected
66v / 0.47K = 140ma
140ma * 66v = 9.2W max surge - very short, so much lower W is adequate, but a 10W unit will survive a dead short to ground - which is extremely unlikely to occur.

The resistor can be a 470ohm at 1W or greater (a 1/4W will work but I tend to like the 1W and greater units because the larger leads are more robust for vehicle mounting, but that's a mounting, not an electrical consideration)
The diode can be a common 1A diode (1N4002, 1N4003, 1N4004) or 3A (1N5401, 1N5402, 1N5404) part as available.

xt90s connectors have built-in precharge resistors. Sadly very low values (<10 Ohm), but so far the work for me. I use 48V and dont hear a spark when connecting.

inedible said:

I recently blew out the stock chinese controller in my scooter and have decided to replace it with this kelly KEB controller, but I'm having some trouble understanding the "precharge circuit".

Here's the diagram in the manual:

My previous controller didn't have anything like this. The key switch went straight to the PwrOn wire on the controller, without all this convoluted relay system. However, reading up on it, it seems this is necessary for like charging up the capacitors in the controller or whatnot, and without it these controllers are known to burn out.

So, I've got a couple questions.. They don't mention anything about what sort of value you ought to use for this "main contactor". In fact it's never mentioned anywhere in the manual. Am I to assume I need to find a relay that can switch the full load of my bike? 66V, 60A? That seems like a lot for most relays. Do I need to find an automotive solenoid or something? Also, it looks like the coil needs to take battery voltage? All the relays I've ever seen have taken 12-24v for the coil.

Then, if I'm not mistaken, this 10W resistor is going across B+ and B- at all times, even when the bike is switched off? Isn't that A: going to waste ten watts for no goddamn reason, draining my battery? and B: going to get very hot, and I'll need to heatsink this resistor?

Following this line of reasoning, I got to wondering if I should put in a switch to switch on the precharge circuit, then, what if I put in a relay to switch on the precharge circuit when I switch on the bike, leading to an infinite loop of relays and me questioning my sanity as well as the need for a precharge circuit in the first place.

Help!

Click to expand...

I'm about to do the same thing, how did you go? wanting to use the smart precharger but 50ohm is pretty different to the 1000ohm 10w kelly recommends. Going to use 72v (60a cont, 90a peak) lifepo4 battery with KEB72601 kelly

Hi People,

I'm happy to have found this forum and this topic, so I signed up straight away.

I am a dutch guy, and in Holland, speed with an electrical bike is unknown.. Nowhere to get info.

I have been experimenting with my china electric scooter for a few months now, it is a dual engine 2x2800w powered machine, with 2 controllers. It is very very fast already, but I decided to take it a little further and replace the 2 controllers, 45A each, for different ones, the engines can handle a lot more. It is a 60volt bike, with 46Ah Panasonic battery pack.

I replaced 1 controller for a 60A replacement.

I made the new controller work, but couldn't get it to work together with the other 'old' controller, because the fabric which made the scooter, made it impossible to do that by securing the controllers somehow.
Ofcourse I tried, but that ended in a plastic burn smelling old controller.

So I decided to buy a Kelly controller..

After a few weeks waiting, it arrived.
I started to read the online wiring details of the Kelly(KLS 7218S) and.. Main contactor.. Diodes.. Precharged resistors.. I have never heard of this..

So now I am stuck with a Kelly Controller, my hands are itching to just try some idea's, but my common sense tries to tell me to stay patient..

I used the drawing from before in this topic, and drawed(very badly) my setup, I want to give it a try.

Can you guys tell me what happens what in this exact setup, when I connect it? Will I blow up my new house AND scooter, or do I get to Live and drive Proud?

Attached the drawing of the situation,

Greetings,
Bas

Wait so if you have a 2 position switch and 12v contactor you could the first position for precharge and second for activating the contactor?

inedible said:

I recently blew out the stock chinese controller in my scooter and have decided to replace it with ... kellycontroller ... but I'm having some trouble understanding the "precharge circuit".

Click to expand...

I recommend a contactor with built-in pre-charge circuit like a Tyco EV200 which I use on my bike without any precharge. Note that it can handle 500+A. Waterproof too.

http://www.rec-bms.com/datasheet/Technical_datasheet_Kilovac.pdf

Michael

P.S. Sometimes EV200s show up used here: https://www.evwest.com/catalog/index.php

https://endless-sphere.com/forums/viewtopic.php?f=31&t=96675

Hello, I just bought an ASI Bac8000 controller and it requires a precharge circuit. I would like to automate the exclusion of the resistor once the main relay is turned on. So could it be okay? Can I use a 5 pole 12v relay taken from a car or will it burn out? Do ANL fuses also exist for 72v or just 12v? Thank you

View attachment IMG_20220531_120607.jpg

MJSfoto1956 said:

inedible said:

I recently blew out the stock chinese controller in my scooter and have decided to replace it with ... kellycontroller ... but I'm having some trouble understanding the "precharge circuit".

Click to expand...

I recommend a contactor with built-in pre-charge circuit like a Tyco EV200 which I use on my bike without any precharge. Note that it can handle 500+A. Waterproof too.

http://www.rec-bms.com/datasheet/Technical_datasheet_Kilovac.pdf

Michael

P.S. Sometimes EV200s show up used here: https://www.evwest.com/catalog/index.php

Click to expand...

Might be confusing the coil economizer with a pre-charge resistor. More below.

To help visualize this for people trying to wrap their heads around the why of a pre-charge circuit, imagine a capacitor as a water tower. A water tower helps store water to even out demand. A capacitor is almost the same but for electricity.

A pre-charge resistor makes a restricted connection between the capacitor bank and the power source (battery) to slowly bring up the capacitor voltage. This avoids the surge and spark that would otherwise happen. Capacitors can move power very quickly, the pre-charge resistor is used to slow down how fast they fill up (get up to battery voltage.) This limits the rush of energy going to try to fill them (inrush.)

A coil economizer drops coil energize power after the initial turn on. The contactor coil needs more energy to close the contactor initially but once it's in place the power to keep the coil energized can drop quite a bit. The coil economizer takes care of this. It's probably similar to a peak and hold injector circuit in there.

A contactor should not have a pre charge circuit built in or it would never fully disconnect the battery as expected.

The danger of leaving a pre charge resistor connected is the controller has battery voltage (high voltage?) On it when you think it might be off and empty. Capacitors can store battery voltage for a long time. The capacitors should be discharged before handling anything inside the controller. It doesn't mean you have to disconnect the pre charge circuit but you have to realize there's power in the controller and back feeding to the "off" side of the contactor as well with the contactor off. It could be a life ending mistake depending on battery voltage.

Parasitic power draws could still sap power through the pre-charge resistor if it stays connected. Some have almost 0 power draw, some draw a bunch.

Gianluca0, your circuit is incorrect in a few ways. Your relay and contractor coils are in series, they should be separate for a few reasons. The pre charge is not doing its job as sketched. Also each relay coil is getting half voltage. Ideally you have 2 steps to turn on, one to energize the pre charge, then once it's charged, one to energize the contactor. The once it's charged part could be you manually flipping switches after a delay, a timer, or something to sense battery voltage vs capacitor voltage and turn on the main contactor when ready. There's the battery connector with a pre charge resistor in it as well but it's not typically as straight forward as it sounds.
A car relay is usually only rated for 12v. You can find some rated higher with a similar Bosch relay footprint and still have a 12v coil.