Re: [electricboats] Contactors and SSR's

One other question I had - and hope one of the experts can answer this:

I don't see a max voltage rating on the contacts for any of the contactors.  Only the voltage of the coil, and the amperage limit of the contactors.

Is it safe to use a 12V contactor (low switching voltage going to the coil) to switch a 48V battery bank?

Ryan,

Thank you for the second contactor suggestion (from Amazon) - more affordable, but more importantly - that one appears to be intended for DC, whereas the original Thunderstruck suggestion was for AC.  If it's electromechancial, might work??  I'm not an expert there.   I know it wouldn't work to use an AC solid state relay in a DC circuit.

As someone else mentioned, the golf cart contactors are frequently used with the flyback diode on the coil, which is probably important at these voltage levels.   I'm not sure about the "precharge resistor".  I agree with the implementation if you're switching the motor on and off directly.   However, I'm assuming that for a 48V system with a 500 ohm resistor, you're adding about a 100mA CONSTANT load this is always there.  Since I'm using the contactor to switch on and off the battery bank, I don't want that load when the contactor is turned off.   And, since the controller should be powered down when the battery bank is switched on/off - the resistor shouldn't be needed (there should be no load when the contactor is switched on or off).

On Tuesday, June 9, 2020, 09:02:59 AM CDT, Ryan G via groups.io <ryanwestbrookcary1=yahoo.com@groups.io> wrote:

Here's another more affordable option than thunderstrucks offering:

https://www.amazon.com/200-Volt-Main-Contactor-Solenoid/dp/B00K1JB5NQ/ref=mp_s_a_1_3?dchild=1&keywords=48v+wireless+contactor&qid=1591710706&sr=8-3

Looks like yours is still lighter on the coffer though. 

I know that there are some that fortunate enough for see "money as no object", and am happy for them. But personally, I spend a chunk of my time looking for the ways I can do what I am trying to do affordably, and using a $40 or $50 cart/industrial relay instead of a specialty $125 relay that does the same job is a perfect example of the kind of though that makes these projects even possible on my budget. 

On Tue, Jun 9, 2020 at 9:37 AM, ryanwestbrookcary1@yahoo.com

<ryanwestbrookcary1@yahoo.com> wrote:

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