The Best Value Wattmeter

[Deleted member 4366]

Are you using the KU93 with a LED panel? If so, you can pickup the 36v from the red wire that goes into it. If no panel, you put a switch on the ignition wire and power the wattmeter from the battery side of the switch. With the control panel or ignition switch switched off, no power goes through the controller, so there is no consumption. The only consumption from the battery will be the blue LED and the wattmeter. The GT wattmeters have a backlight, which takes a small amount of power. The other types without the backlight consume negligible power. Stick a bit of black tape over your battery switch to stop it glowing.

 

[jonathan75]

Are you using the KU93 with a LED panel? If so, you can pickup the 36v from the red wire that goes into it. If no panel, you put a switch on the ignition wire and power the wattmeter from the battery side of the switch. With the control panel or ignition switch switched off, no power goes through the controller, so there is no consumption. The only consumption from the battery will be the blue LED and the wattmeter. The GT wattmeters have a backlight, which takes a small amount of power. The other types without the backlight consume negligible power. Stick a bit of black tape over your battery switch to stop it glowing.

Fantastic. Yes I do have an LED panel. However the red wire leading to it is incredibly thin, suprising to think there's 36v going through that! Still it's good to not have to splice into the thick battery positive, always slightly disconcerting.

 

[jonathan75]

I've read that the wire can cause resistance of 1 to 1.25v per metre - that's 2-2.5 volts if I attach the wattmeter to my handlebars, instead of putting it in the controller bag with a very short wire. That sounds quite significant, maybe a loss of 5-6%+ of power and thus efficiency, so shorter rides to empty. Is this true?

If it's true I don't know why anyone bothers mounting wattmeters or cycle analysts on the handlebars.

 

[Deleted member 4366]

The loss of power doesn't account for much. I think I calculated about 4 watts for two wires going up to the wttmeter and back. With one wire, it'll be about 2w. Use wire no thinner than 14g. 12g would have less loss, but is more ugly.

This is why I do the remote shunt mod. There's no losses at all then.

 

[jonathan75]

Yes I'm trying to make a virtue of well-ordered ugliness on the bike at the moment, thankfully the frame is black-coloured. Thanks D8veh.

 

[jonathan75]

The wattmeter is working well inside the controller bag at the moment pending being mounted on the handlebars - but is there

1) a cheap way of having one sit next to the battery while it's being charged, i.e. that isn't attached to the bike frame, so I can see the volt level while sitting in a cafe or library with the battery charging next to me?

2) something cheap which will also automatically cut off at e.g. 41v so as not to max-charge?

3) lastly, when balancing the battery periodically (monthly?), for how many hours ought one to run the charger after the battery is fully charged?

Thanks

 

[Deleted member 4366]

You can buy the cheapest wattmeter for about £8. You can cut your charger lead and join the two wires to each side, or you can solder the same charge socket as what's on your battery to one side of the wattmeter and the same jack that's on your charger to the other side, so that you can connect it in or out when charging. It'll show voltage, charge current and amp-hours gone in to yoyr battery.

Why do you want to cut-off at 41v? You'll compromise the balancing if you don't fully charge it to 42v. I guess you've been reading theoretical stuff on ES. Some of this theory is for lithium batteties that were made years ago. Neatly all modern cells have ingredient X in them that combats all the shortcomings. Nobody knows what ingredient X is. They keep it a secret, but each brand has its own one.

Your battery is deigned to be charged to 42v and discharged to 31v. If it would be better to do it a different way, those values would be set in the charger and BMS. Take my advice: Use your battery like everybody else and it'll last a long time. By the time it's knackered, there will be much better ones anyway, so it'll give you a chance to improve something.

Charging your battery to 41v is a bit like in the old days when it cost extra for velour covered seats in your car. The people that paid extra for them wanted to keep them nice, so they put polythene or pvc covers on them.

 

[jonathan75]

I think the main thing which got me was the chart on life cycle and charge level on the Cycle Satiator page. Yes probably was influenced a lot by reading ES.

But I appreciate what you're saying about it lasting ages anyway and the older tech. 500 cycles estimated for 42v charging is a lot - I just get a bit depressed at the speed with which my 14.5ah sags on a run. I think it doesn't like hills as much as I'd like, it's a 270+rpm SB CST HT.

Do you know how long it's right for the charger to be left on while on the battery, after the light has gone green, to balance the cells? And how frequently?

Going to put a 48v on it as second battery. Thought would try to mount 48v upside down under bottom tube, but I fear it might get jiggled around too much on the mount, for its health (?)

I intend to use steel straps slid through small slits drilled through the frame mount slider piece, tightened onto the bike bottom tube with some material inbetween to stop the slider from buckling under the pressure. Possibly drill in a single rivnut or small stud to the frame to stop the whole mounting sliding down the tube. Would have to lose a cog or two from the front derailleur but that's alright.

Thanks

 

[Deleted member 4366]

You can leave the charger on as long as you like. I've left mine on for days sometimes. If your battery measures more than 41.5v after charging, it's pretty well balanced, so no point in leaving it on longer.

 

[jonathan75]

You can buy the cheapest wattmeter for about £8. You can cut your charger lead and join the two wires to each side, or you can solder the same charge socket as what's on your battery to one side of the wattmeter and the same jack that's on your charger to the other side, so that you can connect it in or out when charging. It'll show voltage, charge current and amp-hours gone in to yoyr battery.

Do these 5.5mm things look ok? They share the same connector as my charger/battery but I don't know if they're 36v/48v 2amp capable. Some on eBay say 1 amp only. The ad says that the wire is '22AWG 80 degree 300V cable'.

Thanks

 

[Deleted member 4366]

22g is a bit light. I would say 18g minimum. Also, check the size of the pin in the middle.

 

[jonathan75]

Thank you. It looks like I'll have to buy the connectors and solder on some suitable wire. Do these look good enough? (assuming the pin size is correct, which I will further check).

 

[anotherkiwi]

I like the idea of a watt meter between the charger and the battery. I would probably just cut the wire and solder it in permanently. Tiny green and red lights don't rock my boat.

I too read the satiator page. What I really like is the output and short charging times. Any recommendation for a faster charger? The Alloy Shell 900W LiFePo4/Li-Ion/Lead Acid Battery EV Charger from BMS Battery for example?

 

[Deleted member 4366]

You can't charge a normal ebike battery any faster without damaging it. Forget about that Satiator and all the theory that goes with it. It doesn't apply to our typical applications.

 

[Nealh]

The GT power meter uk price is 12 - 14 quid direct from China you can source them for less then 7 quid delivered.