Electronic Circuits and Projects Forum

Originally Posted by browningbuck

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?

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

Originally Posted by browningbuck

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

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

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