35amp test unit?

Status
Not open for further replies.
B

browningbuck

New Member
well i am trying to build a 35Amp test unit. the idea is a 12V battery will be hooked up for max of 5 sec at a draw of 35A. this is a fairly large draw and i do not know what has a 420Watt device i can use? the power doesnt need to be used. it can be dissipated as heat, or light or... what ever. it is to test the internal connections of the battery to insure that all connections have been tested for QC reasons.

any ideas would be greatly appreciated.
Brian
 
Just use three large 1 ohm resistors in parallel. That would give you a .333 ohm equivilant which would draw 36 amps at 12 volts.

Given the short duty cycle three 50 watt heat sink mountable type resistors would have no problem taking the momentary loads. Typicaly they have 10X surge wattage wattings as well so dumping roughly 150 watts into each for 5 second bursts would not bother them one bit.
 
okay that seem simple enough! but im curious if the draw would be a stable 450Watt (like you are describing).. something is bothering me on the idea and i dont know what it is? you may have to walk me through it sorry...im thinking basically im at 1ohm system with 150 watt (draw 3 parallel 50W resistors) but this seems like the short across the three resistors are going to keep rising in draw until they burn (obviously they are designed to dissipate large amounts of energy, but this seems less accurate than what im after)

im not in any way saying your idea is wrong, just trying to understand it. thanks
 
yeah that was what i was thinking about, but i guess that would be 8X 55w laps.... maybe its what i do? im waiting on tcmtech. i like his idea, just trying to figure out if its stable for testing say 100 batteries over a few hours?
 
Last edited:
Head lights are available in most countries. 450 watt resistors are hard to find.
If you choose resistors you could put them in a bucket of oil or water for a heat sink. (water is non conductive at 12 volts) I have used mineral oil, transformer oil and motor oil.
 
Along the lines of tcmtech's suggestion you could use three of these at about $5 USD each or maybe six of these. The latter able to last longer before getting hot. There are also solutions like using 12 volt heater elements along these lines but as can be seen, that gets costly. Also keep in mind the wire used to and from the load. AWG 10 will give you 30 Amp service and I would opt for AWG 6 to avoid IR loss and heating.

Ron
 
Reloadron said:
I would opt for AWG 6 to avoid IR loss and heating. Ron
Click to expand...

Time to pick on Ron.
Using AWG 6 wire is good engineering practice. It seems strange to "avoid IR loss" when the goal is to have 400 watts of RI loss. lol

ron
 
If you need more wattage capacity just use nine 3 ohm resistors like what RR has linked too.

As far as wire gage goes in typical test lead applications multi strand 10 ga would be more than sufficient for a 35 amp load.
 
browningbuck said:
yeah that was what i was thinking about, but i guess that would be 8X 55w laps.... maybe its what i do? im waiting on tcmtech. i like his idea, just trying to figure out if its stable for testing say 100 batteries over a few hours?
Click to expand...

Headlight bulbs would stabilise the current better than resistors. With a resistor, the current will fall 10% if the voltage falls 10%. With bulbs, the current will fall less, maybe only 5%, if the voltage falls 10%.

If you are testing 100 batteries in say 5 hours, that is 500 seconds of load in 18000 seconds, so the load is only being used 3% of the time. If you are using wirewound resistors like the ones suggested, you don't need a big heat sink at all. I suggest that you bolt the resistors to a flat bit of metal, as you will need somewhere to mount them anyhow. If you have enough space to bolt them down, that will almost certainly provide enough heat sinking for the amount that they are to be used.

Wirewound resistors like that are rated at 5 times overload for 5 seconds, so using three 50 W resistor, totalling 150 W, at 350 W for 5 seconds is fine.
 
Hi Brian,

you could use that circuit with some modifications.

It was designed as a current dump for wind generators to act as a brake in stormy conditions.

The circuit can dissipate a total of 660W for the required time you need for testing.

Connect any required load to the output (preferrably resistive).

The circuit will turn off the MosFets when battery voltage has dropped to a sufficient level.

Omit R7 and C3 for instant action.

Boncuk
 
Can you use an off the shelf car battery tester? Thay have nice big resisters inside.
 

I guess what some of all this comes down to is if the OP wants to actually monitor battery current / voltage or just load the battery for about 5 seconds with about a 35 amp load. My take is the latter. No mention of monitoring or switching the load. So some big load out there and that is about it.

Ron
 
Ron your correct, its a pass or fail, if the battery is capable at 35A then the battery passes. i will of course have a amp clamp on there to monitor rough Amp measurements. i like the water heater idea and i think diver300 touched on a GREAT point. however the stupid head lights seem the most cost efficient and stable and 10awg is design (which is capable of a 35amp design)
 
While headlamps are a novel approach I would use resistors. As to things like inrush current with any incandescent lamp? I figure we are looking at literally milli-seconds in the big picture. Considering the time involved? Looking at 5 seconds using a clamp on to note the current this is not quite an exacting science, a rough pass or fail. The AWG 10 should be just fine.

Ron
 
Status
Not open for further replies.

Similar threads

H
How do I test amplifier speaker output polarity?
2
Replies
25
Views
8K
audioguru
R
Best material to make a bed of nails test jig
Replies
7
Views
2K
unclejed613
B
  • Question
odd signals from transimpendance amplifier
Replies
8
Views
2K
BraveWart
B
A
  • Question
Help designing my own diode tester with decent drive circuitry
Replies
2
Views
2K
Nigel Goodwin
F
DMM test leads that can also fit into 4mm terminals?
Replies
4
Views
2K
ChrisP58
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…