Re: [electricboats] Contactors and SSR's

If you are using a 48v nominal bank with a max amp draw of 50a, but the golf cart contactor should work just fine as the motor that the golf cart relay was designed to potentially energize has a significantly higher amp draw. I looked up the ezgo cart motors yesterday, and the smallest 48v motor they sell is 4hp, so 4hpx750w=3000w

3000w/48v=62.5a

They use the same relay on the 8.5hp motor aswell, so you should have a significant safety margin as far as what it was designed to handle. 

That you intend to use it far below its rated capacity generally means you can expect an extended service life of the part, another advantage. 

And in closing I will say that I feel as you are doing the right thing thinking outside of the box. I usually build all my own stuff out of components rather than buying sets, often using parts that meet the specs I need that were manufactured for another application. This is what allows me to afford my projects, because everyone here will attest that none of this stuff is inexpensive to begin with, and getting others to do the engineering or sell you a "specialty" part can make the war chest dry with a quickness. 

Hope this helps!

On Tue, Jun 9, 2020 at 8:43 AM, Bob Jennings

<heatnh@gmail.com> wrote:

John, can't comment on whether that contactor is correct for your application.

This is the contactor thst came with my 10KW setup. Perhaps you could cross reference it.

https://www.thunderstruck-ev.com/tyco-lev200.html

On Mon, Jun 8, 2020, 12:49 AM john via groups.io <oak_box=yahoo.com@groups.io> wrote:

I'd like to put a contactor or solid state relay between my battery and motor so that I can use a simple toggle switch to turn on/off the battery.   Longer term, the bms could disable the battery, or I could even select between battery banks.

But for now, starting simple with an electrically controlled switch for the battery.

I'm using a 48V system.

Typical max operating current may be as low as 20A, but could get spikes up to 50A.

I've looked at DC solid state relays.  And even found some rated up to 48V.  The problem is that when you read the fine print and reviews - even the 100A  SSR's are not rated for anywhere near that amount of current for constant usage.   (arrrgh!!)

I then started looking at "contactors", and eventually ended up looking at 48V golf cart solenoids.

I've always thought of a "solenoid" in this case as being a really big relay.  It looks like the 48V golf cart solenoids should work for this application:

https://www.amazon.com/gp/product/B07P3GYXFX/ref=ox_sc_saved_title_1?smid=AIMSKPF2F52QN&psc=1

(Note - I'm on fresh water, and the solenoid would be in a plastic case - so I'm not worried about corrosion.)

Is that what I'm looking for, or do I need something that's more "heavy duty"?

I saw references to using a flyback diode on the control contacts - and that seemed like a good idea.  Anything else I need to know?

Thanks!

John