Hi all,

Just cool and damp in NC today after the remnants of that Mexico hurricane (Willa?) passed through, got about 1.5 inches of rain in a day.  Glad that’s gone. 

Anyway, I fell a willing victim to the HF flyer advertising their Centech #60581, 2/10/50 amp 12v battery charger for $29.97 on sale.  So I got one, since I didn’t have anything other than my jump pack in case the minivan battery needs charging.

Question is, after seeing a couple compaint reviews on the lack of power output from the same charger (one said theirs worked on the 2 amp, didn’t work on the 10, and they had no idea how to test the 50 amp emergency start feature), it got me wondering as I’ve never even thought a charger would not output what it was rated at... naive I know but really?  

Knowing that SW had little good to say (in the past) about a particular brand of battery charger that started with a “Schu” due to its DC output voltage floating way high, it got me wondering how I could realistically test the amperage output of the new “still in the box” charger. 

I have the cheapo HF (red) multimeter, and can check a battery voltage well enough but how about the charger output amperage?  

There is one poorly filmed YT video with the identical charger (“how to test a 12v battery charger...”) however the guy knocks his multimeter over twice within 15 seconds and it really doesn’t show me much detail/steps.  Also he tested the charger’s 50 amp output while on the 10 amp multimeter setting, that alone would invalidate his methods as far as I was concerned, and I don’t know much about multimeters...

So if someone can explain a more clear step-by-step way to test the 2 and 10 amp output I’d appreciate it. I don’t care about the supposed 50 amp rating as I’m not concerned with that.

Thanks

A cheap (very cheap) way to measure 50, 100, even 2000 amps for short periods of time requires just a little effort.  You have the red HF meter.  Good first step.  That's the expensive part.  

To measure amps you need 2 parts.  First, a meter that can measure a low voltage, lower the better.  The HF voltmeter has a swich setting for 1000V, 200V, 20V, 2000m (2 volts is 2000 millivolts), and 200m.  The 200 millivolt scale, 0.2 volts, is what you want.  

Part 2 is a resistor.  If you get a 0.001 ohm resistor and pass 200 amps through it you will have a voltage drop of 0.2 volts, 200 millivolts.  From Ohm's law, E=IR.  E, electromotive force, voltage, equals I, intensity of current, amps, times R, resistance, ohms.  So 200 amps times 0.001 ohms, one milliohm, is 200 millivolts.  

Getting a .001 ohm resistor.  You can buy one at Amazon or eBay for about $10 rated for 50 amps continuous duty with an accuracy specification.  If you don't want to spend so much or wait for delivery then just make one.  According to Wikipedia AWG # 10 wire is 0.9989 milliohms per foot.  For all practical purposes that's close enough to 1.000 milliohms per foot.  

The last time I made one of these the purpose was to measure school bus battery current.  The school bus battery has threaded studs.  I made a loop on the end of the #10 wire just the right size to fit the battery stud then soldered the loop.  For the other end I made a similar loop and used a nut, bolt, and flat washer to connect the #10 wire to the battery cable removed from the battery stud.  With a foot of #10 wire in series wit the battery it was almost ready to measure amps.  The resistor current bearing terminals are the big loops.  The voltage drop sensing requires two more wires, one at each end.  These skinny wires only carry the microamps the meter takes.  Any size big enough to be sturdy is good.  Any length that is convenient is fine.  The tricky part is that the sense wires need to connect to the body of the #10 wire away from the end loops and exactly 1 foot apart from each other.  The total resistance loop to loop doesn't matter.  What gets measured is the voltage drop across the #10 wire from one sense wire to the other.  I put the sense wires a quarter inch away from the end loops.  When you solder the loops and the sense wires some solder gets wicked up into the #10 wire.  Wire with solder added will have less resistance than the wire without the solder.  That will make your meter read a bit low.  

At the ends of the sense wires I crimped on female quick connect terminals so the volt meter test leads could conveniently plug in.  A squeeze with pliers can adjust for a good fit.  

This rig will measure up to 200 amps on the 200m voltage scale.  For school bus starting current switching the meter to the 2000m scale will measure up to 2000 amps.  I have seen a DT466 scool bus engine take 800 amps.  The time that the current is on is so short that the wire doesn't really get hot.  AWG # 10 wire is not rated for 800 amps contiuous duty.  

To test your battery charger you might want crimped ring terminals or quick connect spade terminals rather than soldered loops for big battery studs.  I would put the skinny sense wire and the #10 wire in the same terminal and then crimp.  The sense wire will make good contact with the #10 wire while not actually carrying the big current.  This way you get the resistor good for more than 50 amps for less effort.  Just make sure that the points where the sense wires touch the #10 wires are 12 inches apart.  

If your #10 wire is copper clad aluminum the resistance will be too high.  If the copper is undersized, same thing.  The thing to do is get an amp meter and connect battery, amp meter, home made amp meter and a headlight bulb.  If your home made resistor amp meter is close to a regular meter, it's good.  Alternatively you could use the headlight bulb, about 5 amps, and measure that with the HF meter amps function then measure again with the resistor and the 200m voltage scale.  

There are several sources for error.  For a scrap piece of #10 wire don't expect precision.  The temperature of the wire changes resistance.  Flexing the wire changes the resistance.  Mispositioning the sense wires and solder wicking affect the resistance permanently.  Expect 10% error.  

Most amp meters contain a fuse.  The HF 10 amp scale doesn't have a fuse.  If your meter has a fuse and you connect a car battery through the meter the computer startup surge can blow the meter fuse.  This #10 resistor won't be bothered by that.

Now, finally, to test the charger, use a battery with a load.  Use multiple headlight bulbs to run the battery down a bit.  With the amp meter between the charger black and the battety minus you can see what it does.  Once the battery is run down the 50 amp battery boost should show 45 to 55 millivolts, 45 to 55 amps, on the HF meter.  The 10 amp should show 10 millivolts.  If you don't have enough headlight bulbs for battery loading you can use an inverter with incandescent light bulbs like a 3 way 50 watt, 100 watt 150 watt.

KNowing what the charger is trying to do and what the battery is accepting, at the present voltage, is extremely enlightening, and more so the more it is observed charging from different states of charge.


I have a different clone one of these on the output of my charger. It is not perfect in that currents under 0.5 amps tend to be read as lower, but I had one version which was good to 0.05 amps.

https://www.amazon.com/dp/B017YCTRKK/ref=sspa_dk_detail_0?psc=1&pd_rd_i=B017YCTRKK&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=f52e26da-1287-4616-824b-efc564ff75a4&pf_rd_r=EJFDJ9ETCHBRZZMJMHDB&pd_rd_wg=xOAH4&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=sCzEu&pf_rd_i=desktop-dp-sims&pd_rd_r=7c6be697-da13-11e8-9665-8df9d4ca2866

Splicing these inline on the charger output is quite simple and one could simply splice the red wire into the + rather than running the current through the red wire, but the black wire has to be spliced inline as there is a tiny shunt( resistor) inside which allows for the current measuring.

I would not pass more than 25 amps through these continuously.

They also measure amp hours and watt hours, so one can see how much the battery has accepted from the charger, and after laod ing the battery to drop voltage below 12.8v, so that the charger seeks absorption voltage again, one can see just how much more thebattery accepts, indicating that automatic chargers ususally say 92 to 95% is charged enough, when the regularly deeply cycled battery really really wants that true 100% charge at least once every dozen cycles or so.

There are many different clones of the wattmeter linked above.  I have not had that exact clone, but some others said they think it is one of the better ones.  IDK.  I have the GTpower versions a,d the one which did measure low currents quite well was 'Andoer'  I have teh windynation one which comes with 8awg and it regularly freezes up and the watt hour and amp hour displays are off by a factor ov over 2, but instant watts and amps seem quite accurate when it is not frozen.

My portable one has anderson powerpoles on it so i can measure loads of anything getting power through anderson powerpoles in the 15/30/45 amp flavors as these housings are identical and mate with each other.

A very useful tool for those wanting to know amperage is an AC/DC clamp on ammeter, as one can simply clamp it over one of the DC cables and see how much current is flowing through it, meaning no openin the circuit to splice a shunted ammeter inline.

I do have an older schumuncher now rarely used on a battery I dont really care about in my workshop.  it will do sky high absorption voltages and other times it quits extremelty prematurely, and without the linked wattmeter inline on the output I would be mostly ignorant of its bipolar behavior.

But there is certainly bliss in ignorance, and a majority of the world prefers a green light, even if is is silently mocking the faithful believer, while degrading the battery faster than needed, by chronic undercharging.

Tricking automatic charging sources into actually holding absorption voltage, until the battery is indeed fully charged, can be extremely frustrating to impossible, and why I use an Adjustable Voltage Power Supply for almost all grid powered charging. I am approaching my 6th year on my current battery with abut 900+ deep cycles on it, which would have been impossible without this AVPS.

It's a manual charger, so it is essentially a transformer with multiple secondary windings, and a rectifier.

Not much there to test, really, and the built-in meter should indicate something close to max (2 or 10 amps) if you hook it up to a somewhat depleted battery. 

On these two lower settings, you could insert your DMM (in 10 amp mode) inline, and measure the amps, which should roughly agree with the ampmeter on the unit.

Do note if using the 10 amp setting, the battery if not depleted might not be able to accept that much, and if well depleted it can accept much more, and the charger might be able to supply more, thus blowing hopefully, only the fuse in the cen tech DMM when hooked inline.

I've no idea what, if any, voltage regulation there is on these manual chargers and a healthy battery should not be pushed much above 14.8v and an abused battery attempting to have its capacity recovered to some degree should only go as high as 16.2v, and only when closely monitored. The 2 amp setting cannot likely push a battery as high as 16+v but the 10 certainly can.

On another forum they were talking about using this specific charger for equalization charges to 16.2v but I do not recall the details, and whether it was adequate for the task.

Let us know what you find.

There are some very cheap adjustable voltage power supplies that can output upto 36 amps, but their amperage might be unregulated and a depleted battery and a high chosen voltge let out the magic smoke, and they might only go as high as 15.3v

https://www.amazon.com/eTopxizu-Universal-Regulated-Switching-Computer/dp/B00D7CWSCG?keywords=30+amp+power+supply&qid=1540701409&sr=8-3&ref=sr_1_3

I had this eaxact brand pre Meanwell, and I constantly had to fiddle with teh voltage dial to keep it under 36 amps when feeding a depleted battery or it would make a sick clicking noise, and it would only do 15.3v max, and when I got sick of twiddling the voltage i cranked it up and waited for the magic smoke to appear. It took 16 minutes, and then i ordered te Meanwell rsp-500-15. That was 4 years ago

This correction to my post above did not make it inside the edit window:

"It's a manual charger (according to the webpage) so it is essentially a transformer with multiple secondary windings, and a rectifier."


And yes, if the charger is on the 10 amp setting, and, its showing let's say, 15 amps into a depleted battery, then that means wait until the reading drops off some before inserting and using the DMM on 10 amp scale. 

I always assume common sense will be, you know, 'common'....but now and then, reminders are appropriate.

Question, would an AC DC digital clamp style multimeter “clamped” over the positive charge cable (when the unit is on the battery correctly, positive cable to positive battery terminal, negative charger cable to frame) work just as well and just as easy? Amazon has an Etekcity MSR C600 for about $27. ..

On second thought, while it measures AC and DC voltage, it only measures AC current. I’m trying to measure the DC current, correct?

One more electricity noob update. 

So since I have two of the HF red giveaway multimeters, I thought I could “sacrifice” one. 

I connected the new battery charger, (set on 2 amps), to the jump cable jaws of the Centek 3 in 1 power pack, then turned the units both on (switch of jump pack to energize the booster cables, and plugged in the new charger). 

The charger % indicator, as expected, went to the 100% charged side of the scale (left), which it should have as the jump pack had been left fully charged. OK, obviously was outputting current.

Next I momentarily touched the leads of the multimeter (set on 10A and red wire connected to the amp hole on meter) and immediately a “pop” and the red (pos) wire, about 26 guage, of the meter got quite hot.  

I disconnected and turned everything off. Opened the back of the meter, the fuze was still good but the meter would not detect DC volts anymore.  I figured I fried something on the circuit board?  
Nope. 

Turns out, after switching all the two multimeter components around (meters, wire cables, fuzes), everything works except the “old” meter’s wire cables.  I didn’t verify which cable of the set was bad, just that when connected up, the original multimeter test cables didn’t work anymore.

So did the 2 amp current from the charger melt one of the wires inside?  

Could the charger be defective and was passing a lot more than 2 amps? 
Or was that momentary connection the problem? 

Maybe I just need to be kept away from all things electrical? 

To measure amps you need to interupt the circuit, and insert the ampmeter in 'series'. Hooking the meter across the terminals (parallel) while it is in amp mode will damage it, scorch it, or burn up the leads, or the circuit board...probably rendering it useless. You can save the little 9v battery tho! 

To measure volts, you simply touch the probes acoss the terminals. 

Dont feel bad, a $5 Harbor Freight meter is a basic, cheap, beginners meter.

If you spent $200 on a Fluke, and burn it up, the tears would be flowing, and rightfully so.

Minor update, I did go out and check the original test multimeter positive cable/wire, it is the bad one.

Curiously the ohm continuity setting did nothing, it showed “1” for all 4 cables when it is supposed to go down to “0” for a good line These cheap Centeks don’t have the audible buzz setting for continuity but did have the differing ohms settings, though none gave me the 0 reading... oh well, at least I know which of the cables work or not.