Watts Up meter setup on battery with separate in/out leads?

[callagga]

Any advice on how I could use a single Watts Up meter to make notes on "input Ah" and "output Ah" without having to change connecting between charging and usage? I'm happy to have to make manual readings (or reset) in between charging and usage, but didn't want to have to repatch the leads into it each time.

The reason I ask is by battery has separate leads for input (charge) and output (connected to motor). It's a Ping 10AH V2.5 LiFePO4 ( http://www.pingbattery.com/servlet/the-8/lifepo4-lithium-phosphate-iron/Detail )

Background: It's suddenly (hadn't used it for several weeks) started to discharge much much more quick than normal, so I want to measure how much it's charging / discharging)

 

[bowlofsalad]

Attach the watts up meter between the charger and charging leads, charge. Once charging is finished, unplug both the watts up meter and the charger from the battery.

Plug the power leads into the watts up meter, then plug the controller into the watts up meter. Once you are done riding, unplug the watts up meter and plug it into the charger.

Sorry if this is too off topic, but it's worth noting. I don't know if your battery pack/controller come with any sort of pre-charge setup, but it would probably be wise to make sure you have a pre-charge setup between your battery and controller.

Pre-charge is an idea where you use a resistor to slowly and in a limited way, power the capacitors in your controller so when you fully connect the battery power leads to the controller, there is no large spark and and potentially large influx of power to the controller. This saves potential damage to the controller and connectors.

https://www.endless-sphere.com/forums/viewtopic.php?f=2&t=46565 There are different ways to do pre-charge.

 

[dnmun]

you only have to carry current in the negative lead of the wattmeter. you can run the positive wire from the battery directly to the controller and just use a small wire over to the positive of the wattmeter to power it. or you can use an external power source and no voltage input on the red wire at all. just the Ah are measured.

 

[amberwolf]

Any advice on how I could use a single Watts Up meter to make notes on "input Ah" and "output Ah" without having to change connecting between charging and usage?

Given how the WU works, and your battery wiring, it's easy enough.

As noted above, the WU only needs the negative lead switched. The positive can stay connected wherever it normally does.

Does your battery have continuity between charge input positive and discharge output positive? If so, then it's relatively simple wiring, as only the negative WU wire has to be switched.

If not, then you will also need to switch the positive, using a second switch, or a second set of poles of the same switch.


If you only have to switch the negative, then you cna use a doulbe-pole, double-throw switch (DPDT).

I was trying to make a drawing of it but I am really really tired and got confused somewhere along the way. I've attached the drawing I started; someone else will need to correct whatever it is I screwed up.

 

[KINNINVIEKID]

http://www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf

 

[callagga]

thanks for the ideas guys

@amberwolf - I was thinking doing a 3-pole arrangement like this might be good so the middle switching position could be used to have the meter disconnected, to make sure you have a way to reset the meter before going from charging to riding. Does this make sense?

Actually if I wanted to put in a battery backup in place, so that if my battery is dying early I can see the readout on the meter before it switches off, then I might need a separate switch to switch the battery backup connection to the meter correct? Or even just push button to reset (where it disconnects it).

 

[amberwolf]

@amberwolf - I was thinking doing a 3-pole arrangement like this might be good so the middle switching position could be used to have the meter disconnected, to make sure you have a way to reset the meter before going from charging to riding. Does this make sense?

Yeah. . just make sure you figur eout the real wiring, cuz I am sure my drawing is wrong. :/

Actually if I wanted to put in a battery backup in place, so that if my battery is dying early I can see the readout on the meter before it switches off, then I might need a separate switch to switch the battery backup connection to the meter correct? Or even just push button to reset (where it disconnects it).

If you look at the WU manual it has a pinout for hte little connector on the side that lets you connect a separate "backup" battery (like a little square 9V) to it so it doesnt' lose the settings. You could even get complex and put a little simple transistor circuit on there that turns the backup battery on automatically as soon as there's not sufficient voltage ot the main source input, and turns the backup off as soon as there is sufficient voltage there. I think it als ohas a reset pin in that connector.

 

[callagga]

I think it als ohas a reset pin in that connector.

thanks for the tip! Hadn't realized this

 

[callagga]

Does your battery have continuity between charge input positive and discharge output positive? If so, then it's relatively simple wiring, as only the negative WU wire has to be switched.

What did you mean here actually? My battery (Ping) has a different set of Pos/Neg leads for both charge and discharge. Just wanted to check whether it's ok to actually connect the positive together here as part of the design? i.e. therefore with one DPDT switch switch the negatives, but have all the positives leads (charger +, battery charge input+, battery dischange output +, watt meters positives on both sides, controller +) connected directly together?

PS. Here's the diagram I just did to show this

 

[d8veh]

That's a diabolical amount of messing about. You can buy a separate wattmeter for your charger for $10.49.
http://www.ebay.co.uk/itm/New-Digital-LCD-60V-100A-Balance-Voltage-RC-Battery-Power-Analyzer-Watt-Meter-/271336914329?pt=UK_ToysGames_RadioControlled_JN&hash=item3f2cf0bd99

 

[callagga]

I agreed Wanted to get something working to this weekend to help fault find. Got it working ok actually.

That's a great price though, I'd just been looking at the cost of the wattsup meter..

 

[callagga]

Update: Whilst setting up a way to make it much easier to monitor usage, I actually found a bad solder joint on the line between the charger and the battery charging input. This would explain perhaps why I did a charge then drain test this afternoon and got 9.44Ah out of the battery which seems good (i.e. assuming this is a good result, it may have just happen to be a good charge). What I mean is it may have been perhaps the battery hadn't charged properly perhaps in the previous few rides? I've resoldered it so I'll see if that makes the difference.

 

[dnmun]

how did you measure 9.444Ah? i thought you had no watt meter. i found the watts up to be inaccurate and it would continue to run the timer as long as the power was present. there is a reset pin on the end of the watt meter where the auxiliary power plugs in. you can see the little voltage step image on the case where reset pin is located. bring that pin up to 5V and then drop it back to 0V and it is reset.

the RC power meter is better and you can buy two for the price of one watts up, even before shipping costs from HK.

 

[callagga]

yeah I had one but wanted to measure charge & discharge - didn't know there were other meters that were so cheap