T-Pain Is On A Boat: Re: [Electric Boats] Shunt?

Thursday, August 1, 2013

Re: [Electric Boats] Shunt?

I just bought this,
http://www.ebay.ca/itm/Universal-Bright-Blue-199-9A-Ammeter-Input-5V-18V-Shun-/350317874994?pt=LH_DefaultDomain_0&hash=item5190928f32

And this,
http://www.ebay.ca/itm/Universal-Blue-LED-Volt-Current-voltage-panel-meter-/200388743329?pt=LH_DefaultDomain_0&hash=item2ea81990a1

I was able to order them calibrated and including the shunt. They do sell separate shunts.

mattelderca

From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Thursday, August 1, 2013 5:21:26 PM
Subject: [Electric Boats] Shunt?

Does anyone have a favorite place to order an inexpensive shunt?

Also, is there a better value to use than what I've got? (75mv @ 200A)

Here's the details:

My current setup is a Torqeedo 2T, which is on a 24V system, with a max of 2000W (~100A).

I'm driving this with two banks of group 27 FLA batteries. I can drive 100A for a SHORT period of time, but will typically run much lower than that.

Two banks are switched through a "1 / 2 / both / off" battery selector switch. Grounds for both banks are connected, then go through a shunt rated at 75mv at 200A, then on to the motor.

I have a simple / cheap voltmeter across the shunt, and it does a good job of telling me the voltage drop - which I can then correlate to A and W.

The problem with this shunt is that it's odd numbers, so you almost gotta put your phone in "calculator" mode (I carry multiple VOM's on the boat, but no calculators...) so that you can figure out how many amps / watts correlate to the voltage across the shunt. I'm thinking if I had a shunt that was something like 200mv at 200A, the math would be a lot simpler....

But I can deal with the math. At least if I have a meter, I know 35mV is pretty close to full power for the motor.

The boat will go about 4mph at about 15mv, and that doesn't drain the single battery tooooo fast.

Now, someone (Mike?) had made the comment before that due to the Puke (puekart? ) Battery effect, the batteries will last much longer if they are discharged more slowly, and thus I'd get longer life if my batteries are tied in parallel instead of draining one bank at a time.

AMAZINGLY - my limited test runs seem to validate that!

It would be fun to have a shunt on each battery bank, and run two voltmeters - so that when I tie the batteries in parallel, I can see what the load on each bank is!

(since one bank is rated at 160 reserve minutes, and the other is rated at 182 reserve minutes).

Hence - I need to order a matched pair of shunts, and if there is a better value to use, it might even make the math easier.

200A is probably good - then I've got plenty of buffer so that I don't overheat the shunts if I'm running for a while.

I probably don't need to go any higher than that though.

And they don't seem to have a huge range of values out there - so 75mv at 200A may be it... though 100mV@200A would be easier...

Thoughts?

__._,_.___

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