poor person's doc wattson alternative ?

N

needWheels

1 kW
Joined
May 27, 2008
Messages
481
So it's going to be awhile before I can afford/justify a $50+ doc wattson / watt's up.

Since I am using simple SLA arrangements, would it not be possible to just monitor actual voltage which goes down over time with SLA (unlike lithium etc. which is always constant?)

Is there not a $5 circuit I can buy to do this? I have an ancient analog mini-meter I no longer use which I might be able to take apart and make smaller if this concept is viable?
 
you don't need to run one... but save the money for a doc wattson at least.

you could run a multimeter setup but its not worth it

Also there are ammmeters but messy to setup i guess.
 
needWheels said:
Is there not a $5 circuit I can buy to do this? I have an ancient analog mini-meter I no longer use which I might be able to take apart and make smaller if this concept is viable?
Click to expand...
These go on sale frequentlly for 2.99
90899.gif

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899

These would be da'shit, in a row of four on your bars (3.99):
95779.gif

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95779

:mrgreen:
 
Yeah, there aren't too many road Ah meters out there. I went with the Doc Wattson because it was the cheapest I could find. Knowing min/max voltage and such is nice, but all I really needed was something that counted Ah used, and that's it. Unfortunately, I know of no commercial product that will do this. :?
 
If you're knowledgeable about digital design and electronics, you could make it. :D

Using a shunt resistor, you can measure the voltage drop across the resistor using a cheap voltometer and then calculate the current directly from that in your head(Or you can just put the corresponding current along a voltage difference gauge's rim for quick reference). To calculate the amount of amp-hours consumed, you'd basically just have a to do a sum of the amp-hours measured at specific time-intervals. I.E., If you're reading X amps at some time period with an interval of a second, than you've basically "burned" approximately X amp-seconds for that second. Take the sum of those amp-seconds and do the conversion of 3600 amp-seconds in an amp-hour and you have a useful metric.

But making something useful with digital electronics is still expensive: The Doc Wattson is probably your cheapest "comprehensive" solution.
 
I took an electronics 101 course in college but only know/remember enough to be dangerous, lol.

I might just try to find another cheap digimeter and disassemble it to make it smaller.
I like how the harbor freight one has it's own on/off switch so you can leave it locked in the volts mode.
My current one (walmart $10 special) is just like that but no switch.

no stores near me and unfortunately shipping kills that deal
by the way, here's a coupon to make that meter $2 in-store:
http://www.harborfreightusa.com/savemore/
also http://www.harborfreightusa.com/buynow/
and http://www.harborfreightusa.com/html/wkend0608/usa_cpnsave.html
(dayum, next town I live in must have a harbor freight and a frys!)
 
I used that analog ammeter that Tyler suggested for a couple of years along with a DMM for volts. Doesnt give all the info U need, but definitely cheep. Works good for immediate feedback of amps and overall volts under load. Good enuff!
otherDoc
 
Just out of curiosity, will a cheap multimeter allow you to keep both probes (voltage and current) attached at the same time so I could rotate from voltage reading in parallel to current reading in series? Or will I blow something up?

I noticed my walmart multimeter has a 10a max limit so I bet that's not going to work.

I'm going to find a friend who lives in a city with a Harbor Freight and have them mail me a few of the $2 meters so I can accidentally blow them up, or screw up "downsizing" them, lol.

(in fact execept for the case colur and on/off switch and that weird blue port,
my multimeter looks the same as the HB one)
 
You can't hookup a single meter to read V & A at the same time (by switching the dial).

I suggest docnjoj's method for the ammeter. (originally from Xyster or Gruber ?)

:mrgreen:
 
TylerDurden said:
You can't hookup a single meter to read V & A at the same time (by switching the dial).

I suggest docnjoj's method for the ammeter. (originally from Xyster or Gruber ?)

:mrgreen:
Click to expand...

You could hook up a single meter to measure the potential difference(voltage) across a shunt resistor(Whose resistance is known) and then add the appropriate markings to the face of the dial to indicate current, which requires pre-calculation via current=voltage/resistance-of-the-shunt, of course.
:wink:

But the voltage dial would have to have a fairly high resolution to accurately indicate a voltage drop that would probably vary between 0 to 1 volts, the range depending on the resistance of the shunt. A higher resistance would increase the voltage range, but that would also increase the amount of power that's burned off in the form of heat in the resistor and so less power would be delivered to the motor. So, you'd basically have to carefully balance the resistor/voltage-range/current-range and the cost of a fairly accurate voltage dial(I don't really know where you'd get a shunt-resistor, but I'm sure you could find one cheaply.). But, I wouldn't think sufficiently accurate voltage gauges on eBay would be that expensive: They were invented back in the Neolithic era, right?
 
This isn't helping my pack-rat habits but I found this old camcorder battery tester in my junk pile:
http://www.smcelectronics.com/PICTURES/VIDAC12-L.JPG
(original packaging, $13 at radio shack in 2001, lol)

It's the size of a book of matches which is nice. Problem is vhs-c battery was only 6 volts.
There's a big fat resistor inside that probably drops the voltage for the circuit eh?
I bet I could change that out to something to handle the 12v if I read the bands
and figure out what it is. I'll borrow a camera and see if anyone here can tell me.

the packaging says not to keep the tester connected for more than 10 seconds or it will overheat, lol
I'd have to make it push button...
 
I used those digital meters to restore the dashboard of an old motorhome I was restoring. Looked and worked great. Absolutely not cheep!
otherDoc
 
Ben said:
Couple of these would be rather cool on the bars.
Click to expand...
Those look lovely but scream "STEAL ME" to the druggies.
My bike is my "workhorse" and unfortunately has to be parked in some sketchy areas.
That's another reason why even if I could afford a doc wattson I'd think twice about it.
A $2 meter is another matter (but I still suspect they'd try to steal it if I didn't make it look trashy)
 
Sorry for a stupid question but I'd rather ask than blow something up...

if I want to see real-time voltage while I am riding, do I just wire the multimeter
to the battery in parallel to the controller hookup? Or in serial?
 
It's a shame these things only go to 14v
http://www.dealextreme.com/details.dx/sku.11995

Really nice selection of $10 panels, too bad shipping is also $10 since they are in China:
http://www.virtualvillage.com/Store/Search.aspx?&Page=1&Sort=1&key=panel&sp=1.00&ep=10.00&scat=17171
 
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