Tuesday, June 9, 2020

Re: [electricboats] Contactors and SSR's

Don't get me wrong, if someone lacks sufficient knowledge to safely and effectively engineer and build their own system, they should absolutely go with a turn-key offering and pay someone else the big bucks necessary or not mess with it at all....
But this from is really representative of a niche market of, from what I can tell, mostly passionate diy-ers that have an interest in understanding what they are trying to build or re-fit. Some here look for advice on turn-key systems, but many seem to be more interested in the technical aspect of how to make it work, and come here to ask those with the knowledge and experience for advise, a wise move if they themself lack it. Once someone has a basic understanding of electrical theory, it is not hard to figure out what components will work together. And sometimes, in researching alternative options, great innovations are made (keep in mind that the guys at thunderstrck and similar companies really just figured this same stuff out themselves and sometimes we find ways to improve the kits they offer by just swapping one of their components)

Even the Curtis controllers they offer can be bought at around half the price they want on places like eBay and Amazon. 

All that said, I just hate how the industry leaders like to make everything a "rich mans sport"
 I am reminded of the gear reviews and suggestions in rags like f&s, to see what they recommend one could get the impression that you gotta have a six figure salary to even consider deer hunting! But au contraire, I have put much venison on the table with a $70 Moisan nagant wearing gi surp bdus 

For those on a budget, a little interest and education can potentially make something possible that otherwise would not have been due to finance. It's not a coincidence that people like Edison and tesla came from meager beginnings... if they had been better off, they may never have had the ambition to develop the ideas they had into actual things. 

Like you say, just my 2 cents

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.






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:


(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

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