Wiring in a watts-up - how long is too long?

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wookey
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Wiring in a watts-up - how long is too long?

I have a Sakura s50 (erato 06), which is a straighforward 1500W BLDC motor with 48V, 40Ah lead-acid battery.

I also have a watts-up and want to wire it in to get some better data on the bike (with a view to swapping to LiFePO4 in due course). However the watts-up has both shunt and display in one unit so I can either mount the meter low at the rear, where I can't really see it (not safely whilst travelling), with short wires (~0.5m), or on the dash with quite long wires (3.5 - 4m). I could arrange it so that only the Ground wire is long - the positive wire could be 50cm as before.

Now, I have read that the inductance of the wires between battery and controller matters - too long and I will get inductive spikes that could nuke my drive mosfets. So, how do I decide what consitutes 'too long'? Have lots of other people put in watts-up meter wired all the way to the dash and back and no-one had any trouble?

The controller PCB was market BLC3000 but I found no info on this. It is surface mount with 12 MOSFETs and a PIC 16Fsomething doing the work. Looks nicely made (better than I was expecting to be honest).

One other thing - the controller has 2 wires coming out for the three motor phases and the GND wire, but only one for +V. These all change back to one wire at the connectors~10cm from the contoller. Is there any reason for this other than wire gauge? (and if not why not do it for +V too? - surely GND and +V have the same current).

I ask because I want to rewire everything in powerpoles rather than ring+2BA brass bolts which is fiddly to take to bits and uses a load of insulation tape every time I change anything. But for powerpoles I need single wires. (Or some kind of high-current splitter). I suppose I ought to do some sums really. I have noticed that 30A powerpoles are a bit weedy really. Peak current is 50A and the wires _barely_ fit in the crimps. I guess I should buy some of the larger 45A powerpoles (or double everything up).

I would include a pic of the inside of the controller, but my camera is very poorly and none of them came out.

reikiman
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Re: Wiring in a watts-up - how long is too long?

I've seen pictures of small scooters where a Watt'sUp was taped to the handlebar. This meant obviously having to run power wires all the way to the handlebars before heading back to the motor. Clearly that works for some people for some definition of works. I wouldn't recommend it for the reason you say.

I'd instead recommend getting the high power rate Cycle Analyst.

It uses a remote shunt and tiny wires to the dash. The Cycle Analyst does more features than the Watt'sUp e.g. recording AH usage over multiple trips e.g. speedometer ..etc..

Another consideration with the Watt'sUp is whether it can handle the power of your scooter. It has a spec'd limit on the number of amps it can safely do. That spec'd limit may be higher than your scooter will draw but that may not be the whole story. Today as I pointed out in another thread I was testing my Headway pack using a Watts'Up and let 300 watts or so run for an hour or so. When I came back to look the display was darkened and the Watts'Up case was warm. The case wasn't dangerously warm but LCD display darkening is I think an indication of heat. I'm doubting the Watt'sUp can handle 1500 watts for very long but haven't tried it myself.

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

antiscab
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Re: Wiring in a watts-up - how long is too long?

+1 for the cycle analyst.
i to initally bought the watts up over the cycle analyst due to the price, but ran into the same problem you did.
my suggestion is to forget about teh wattsup and buy and cycle analyst (the watts up comes in handy for bench testing batteries, so not all is lost)

One other thing - the controller has 2 wires coming out for the three motor phases and the GND wire, but only one for +V. These all change back to one wire at the connectors~10cm from the contoller. Is there any reason for this other than wire gauge? (and if not why not do it for +V too? - surely GND and +V have the same current).

I ask because I want to rewire everything in powerpoles rather than ring+2BA brass bolts which is fiddly to take to bits and uses a load of insulation tape every time I change anything. But for powerpoles I need single wires. (Or some kind of high-current splitter). I suppose I ought to do some sums really. I have noticed that 30A powerpoles are a bit weedy really. Peak current is 50A and the wires _barely_ fit in the crimps. I guess I should buy some of the larger 45A powerpoles (or double everything up).

wires between motor and controller for the majority of BLDC setups are as follows:
3x thick main power wires (usually yellow green purple)
3x thin wires for the hall effect position sensors (also usually yellow green purple as each one is association to a specific phase)
1x gnd to power the sensors
1x v+ to power the sensors
1x temp sensor wire

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

little
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Re: Wiring in a watts-up - how long is too long?

hello sir, I (account : little ) have post the circuit diagram under the menu: control system:

there are three for your info.

http://visforvoltage.org/forum/6800-electric-scooter-circuit-public

wookey
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Re: Wiring in a watts-up - how long is too long?

Hmm, yes. The cycle analyst is clearly a superior piece of kit in a whole range of ways, but it is also 3-4 times the price of the watts-up, and I already have a watts-up. I would seriously have considered a cycle-analyst had I known about it, and I might still... I can split the case and install a remote shunt for the watts-up, solving the main issue, at the expense of spoiling the weatherproofing, and I'm not sure how accurate things are with a random shunt and wiring, at these very low shunt resistances.

I'll see how it holds up for a few rides (at least to get some max readings and energy-usage numbers for my commute), then think about more mods or shopping for better kit. See if it gets too hot (spec suggests it should be OK up to 50A continuous). It's currently hanging in the air-flow so should be fine.

Thanx for the circuit diag - interesting. That does look very similar to mine. I need to grok the speed-control bit to see if it can be nobbled to go a bit faster :-)

Antiscab, yes, I've got that for the basic wiring. The point is that the power wires (3 for motor and GND) are run as two wires out of the controller, but joined at the ring crimp after 10cm or so. Then the wires to motor and batts run as a single wire - which just seems a bit odd, especially as it's not done for the +VE wire.

Wookey
Sakura s50 (Efun A)

mf70
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Re: Wiring in a watts-up - how long is too long?

The Watts Up uses an internal shunt, but it can be removed and used as a remote shunt:

http://www.rc-electronics-usa.com/special-mods.html

I've used mine that way for the last year. My only complaint is that it doesn't count AH backwards when under reverse load. It has to be physically turned around to read charge AH after reading discharge AH.

They also sell separate shunts, but I mounted the one I removed on one of the RadioShack grub-screw terminals.

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