# Testing Car/Boat Battery Chargers?

8 posts / 0 new
Bright_Mike
Offline
Last seen: 2 years 3 months ago
Joined: 03/09/2014 - 11:30
Posts: 331
Testing Car/Boat Battery Chargers?

Wondering how to test these? 12v lead acid battery charger for car and boat batteries I believe.

What V and A would be expected? Seeing a lot of different stuff on the internet, that doesn’t look right.

Have a Harbor freight 2/10/50A that doesn’t seem to be working right, and a 3A Schumacher that is slow. Like to get recommendations on which model (or module?) to buy. Any DMM’s go over 10A to test these?

Edited by: Bright_Mike on 09/29/2017 - 14:32
Lightbringer
Online
Last seen: 1 min 53 sec ago
Joined: 08/30/2016 - 14:12
Posts: 16183
Location: nyc

I “inherited” an ancient cinderblock of a charger which is indestructible, so I don’t have any need/interest in new chargers, but I know that DMMs will go pouf rather permanently if you hit the unfused input with more’n 10A.

Best thing to do is to use a lowlowlow resistance current shunt and measure the voltage drop across it. So if you have a 10mΩ length of wire, 1A will generate 10mV, 10A will generate 100mV (0.1V), etc.

Pick a sufficient gauge of wire, look up wire resistance per foot, then measure out the length of wire needed to get the right resistance.

Quickie (per http://www.daycounter.com/Calculators/AWG.phtml ):

20ga wire = 0.0333Ω/m = 33mΩ/m

You want 10mΩ, so that’s 10/33 m or about 1/3m or about 1ft.

You don’t need to go crazy with a ruler as other variables will throw the accuracy in any direction. You mainly want a ballpark figure, I imagine, no? Hell, the resistance of the wire goes up/down with temperature, so unless you got a thermometer, too, …

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Pete7874
Offline
Last seen: 4 hours 45 min ago
Joined: 11/23/2011 - 16:47
Posts: 3495
Location: USA

Charger/maintainer:
http://a.co/69jWbK5

Quote:
Any DMM’s go over 10A to test these?

Clamp meters do, easily.
Lightbringer
Online
Last seen: 1 min 53 sec ago
Joined: 08/30/2016 - 14:12
Posts: 16183
Location: nyc
Pete7874 wrote:
Quote:
Any DMM’s go over 10A to test these?
Clamp meters do, easily.

AC only, generally, at least the cheapies. Those that measure DC are pricier.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Pete7874
Offline
Last seen: 4 hours 45 min ago
Joined: 11/23/2011 - 16:47
Posts: 3495
Location: USA
Lightbringer wrote:
Pete7874 wrote:
Quote:
Any DMM’s go over 10A to test these?
Clamp meters do, easily.

AC only, generally, at least the cheapies. Those that measure DC are pricier.

Lightbringer
Online
Last seen: 1 min 53 sec ago
Joined: 08/30/2016 - 14:12
Posts: 16183
Location: nyc
Pete7874 wrote:
Lightbringer wrote:
Pete7874 wrote:
Quote:
Any DMM’s go over 10A to test these?
Clamp meters do, easily.

AC only, generally, at least the cheapies. Those that measure DC are pricier.

Where? Cheapest I’ve seen is about 70. Too cheap to spend that much just for tailcap measurements.

Btw, make sure it actually measures DC, and isn’t just in the blurbs. Half the time those yahoos just vomit out what sounds good, without regard what the critter actually does.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Pete7874
Offline
Last seen: 4 hours 45 min ago
Joined: 11/23/2011 - 16:47
Posts: 3495
Location: USA
Lightbringer wrote:
Pete7874 wrote:
Lightbringer wrote:
Pete7874 wrote:
Quote:
Any DMM’s go over 10A to test these?
Clamp meters do, easily.

AC only, generally, at least the cheapies. Those that measure DC are pricier.

Where? Cheapest I’ve seen is about 70. Too cheap to spend that much just for tailcap measurements.

Btw, make sure it actually measures DC, and isn’t just in the blurbs. Half the time those yahoos just vomit out what sounds good, without regard what the critter actually does.

http://a.co/55NcbI6

It was around \$30 when I bought it earlier this year. It measures DC current just fine. HKJ tested it just recently.

Lightbringer
Online
Last seen: 1 min 53 sec ago
Joined: 08/30/2016 - 14:12
Posts: 16183
Location: nyc

Pete7874 wrote:
http://a.co/55NcbI6

It was around \$30 when I bought it earlier this year. It measures DC current just fine. HKJ tested it just recently.

Oooh. Tempted to get one.

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0