Switch 60v with ,max 30v relay??

Thread Starter

Fhorst

Joined Aug 16, 2019
20
Hi guys and girls, I need your help!

I have several standard 5v relays, you know the type standard blue Square blocks.

They are rated 30v DC or 250V AC

I need to use them for 40-60v contactor, about 0.10- 0.15A current draw.
(11w during making contact, 7w continue)
The Contactor does higher capacity, max 350A..

Voltage difference is between 40 and 60v (officially 48v units)
At both top or low it needs to disconnect / release.
Usual voltage is 50-55v
(16*3.2v nominal LiFePO4)

During testing phase I will switch the relays several times.
After this, perhaps a few times per year automatic release due too high or too low.

Can this be used????

Max 30v (2A) probably for Arc problems at higher voltage with 2A..
My capacity is really low....

And ..
If it does fail, how will it fail?
Keep the contact?
That would be catastrophic..

Or release and no longer work to reconnect??
(Last one not a problem, easy enough to replace)

Or do I need different relay?
PCB design is for this standard 5v units. (See picture, first one I found)

Not sure if there are 5v units that can switch 60v with the same footprint

.thank you for your input!!
 

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Yaakov

Joined Jan 27, 2019
3,316
If you have a relay rated for 30V DC it is not rated for 60V DC. You might find it works or you might find it weeds itself on.

You need a properly rated relay for reliable operation.
 

MaxHeadRoom

Joined Jul 18, 2013
23,342
Whatever cube relays you use, it would pay to remove the sealing 'pip' , used during the de-flux stage, You can see them in the corner on those relays
They reduce the ionization of the relay interior when switching the rated current.
 

crutschow

Joined Mar 14, 2008
27,394
The 30Vdc maximum is at the maximum 2A current to handle the arcing of breaking a DC current, as you surmised.
That's why it's rated 30Vdc but 250Vac.

So, contrary to the naysayers here, I would think that at only 0.15Adc there should be no serious problem with arcing at 60Vdc unless the load has significant inductance, which could be suppressed by a diode (e.g. 1N4002) across the load (a diode across the load or from the output contact [anode] to V+ would be good practice for any load to minimize arcing).

Would there be a serious problem if one of the contacts did weld together?

You could try contacting the manufacturer about this, but it may be difficult to find any contact info.
 

bertus

Joined Apr 5, 2008
21,442
Hello,

This is stated about the contacts:
Contact Data


1. Contact Form : 1H/1Z
2. Contact Material : Silver Alloy
3. Load : Resistive load(COSФ=1)
4. Contact Ratings : 10A 250vac 15A 125vac
5. Minimum load : 100mA 5VDC
6. Max Switching Voltage : 250VAC/30VDC
7. Max Switching Current : 15A
8. Max Switching Power : 2500VA/240W
9. Contact Resistance : 100mΩMax at 6VDC 1A

http://www.datasheetcafe.com/jqc-3ff-s-z-relay-datasheet-pinout/

Bertus
 

Thread Starter

Fhorst

Joined Aug 16, 2019
20
Whow,

Thank you all for your replies!!

Some background might help to understand.
I have 40 kWh LiFePO4 battery, 3 inverters with 3* MPPT solar charge (total max 14.5 kwh)

Naturally the batteries (3 sets of 260Ah, S16) have BMS (Jikong)
I have DIYBMS also, and will Join the 2.
Mostly as the DYIBMS has emergency shutdown options and WiFi.

The 3* solar in are contacted with 50A DC orange Contactors
(See picture)
Not the highest quality, but good enough.
I didn't have funds for space rated Digikey +$100 per relay.
While those use only 2 watt, and these 7w.. for 40 kWh backup, the 3*5w extra is not a problem.
(See picture)

As my system is 48v..
I didn't know better..
I ordered them also 48v ....
I can use a step down (60v max 200w) to one default voltage like 45v but like to keep the parts in the chain as little as possible.
As each might / will fail at one time.
My contactors seem to work without problems at 45-55v
for what I could get, they are build for 40-60v

That's 3 units, each switched by one BMS controller.
Negative wire, NO.
Voltage of the contactors is high, +300v amperage max 20A

Battery contactor is same type 400A.
Obviously uses more power.
11W :)
Max charge / discharge is 200-250A, 40-60v
That contactor will do fine :)

If they where 5v (that is available)it would not even be a question..
But.. I have the 48v.
+ Fluctuating battery voltage 40-60v
I can't just spend an other few hundred bucks just to replace for 5v units

Why use the relays?
PCB is designed with it.
(DIYBMS) and I already have the partly populated boards (5*) and parts + older controller type and relay boards.

@crutschow
Yeah, a small (or larger) diode might help with arching.
Good tip!

Sorry @MaxHeadRoom
I don't understand "remove the sealing 'pip' , used during the de-flux stage, You can see them in the corner on those relays"

The full information datasheet is attached (LCSC Part #:
C35449)

I'm not enough technical to filter out the needed information from Chinese :)

it's a normally open it normally closed type of switch, and for me, used as normally open.

previous versions of the controller used the Arduino boards, new version has them in the PCB board as part.
More information:
https://github.com/stuartpittaway/diyBMSv4

The relay:(See pic.) And PDF
10A 250VAC / 30VDC or
12A 125VAC / 28VDC

Worse case scenario is the 40v 11w in current: 0 275A
Or
Worse case scenario is the 60v 11w in current: 0 185A
This does it twice.
During start and emergency shutdown (fire, electrocution, (dis)charge below 40 or above 60v)
All should never happen.

For solar charge controller, it can stop a bit more frequent.
If a cell goes above 3.75v

Now the MPPT Is already talking care of the total voltgae.
Jikong does 2A active balance, DIY BMS 1.5A passive and the Jikong (Mosfet based) should stop charge at 3.65v
In theory, It should not happen.

I don't like Mosfet based BMS, they came with the battery packs (BYD) and will usually work.
Several people I know online have had serious problems with Mosfet based, mostly just defective, some have fused mosfets, that keep the charge open (!)

I know solar charge controler can/will fail.
Personally lost 800Ah@48v deep cycle lead acid due defective EASun MPPT, that gave 78v..
(Anyone in Thailand like 1200kg old lead?)
And my previous set of LiFePO4 (80 cells, 280 and 152Ah, 1016Ah S16) catched fire due defective cell that started self discharge, heating up the neighbors, cascade....
It got really hot, like 350-400c, enough to self combust the ox-gard used with contacts.
I got lucky.
Smoke detector alarm
Loads of sand and a space built for this kind of accidents kept it contained.

Now replaced with laser welded pre-compressed BYD battery packs, 60kg each.

Thing is, I can't afford other setback of this magnitude.
($5000)
Needed to get in debt to fix this one, and will be away end this year for 2 months.
Wife and family is here, off grid Thailand
They know how to put out a fire or so.
Not how to repair electronics.

It should not fail again.
Or fail partially

3 sets, each controls its own part.
"Nothing" can go wrong..

Except..
I am using the relay outside specifications, switching 40-60v 0.3A max what is build for 10A@30v

I have several spare.
And they can do.
I tried a few times.
If the software tells it to release contact it should.
If it no longer can make contact due failure from too high voltage, sad but not a probelm.
If it can't release...
Huge probem.
(I have relay based smoke detectors in parallel with emergency button, set to the emergency shutdown contact of the DIYBMS controller board.)

Absolute most important with electrical fire is to stop the source power!!
Here battery or solar.

There is halon like (BC2000?) Automatic fire distinguisher that goes at 68c big enough to stop all..
Room is 2.5m2, distinguisher for 9m2.. lol
Should do the trick.

My gut feeling tells me it shouldn't be a problem.
It's a rea tiny current, 0.15-0.3A max, on a switch build for 10A @30v.
It is far outside factory specifications.
All sellers will advise against it, for this reason.

It's not a probelm, if there are 60v switchable units available to use them, if they have the same footprint.

I can not find them!!!
Loads and loads with the same specifications.
10-25A, all 30VDC

Why ask here?
This is the place where theory and specifications are tested in real life.
400A Chinese contactor is good for 250-300A, not 400...
25% China margine
High space type quality 400A would not Care about 500A..
20% standard under spec. For safely...

Factory standards are numbers totally open to interpretation, depending on source.
In this situation, China.
10A@ 250v.. I would not want to try 2500w for continuous load or switch a few 10.000 times!
It won't do it, even inside specifications
 

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Thread Starter

Fhorst

Joined Aug 16, 2019
20
Use a 30VDC relay to switch a 60VDC relay. If that’s not appropriate, then find another simpler solution.
Simple solution is the solution with minimal parts that can fail.

Adding a relay on top of a relay to switch a contactor...
Isn't simple.

Simple would be to replace the 30VDC with a 60VDC unit.

Except my Google qualities aren't skilled enough to find this type of electronical components.

My best results give units that switch with 48 or 60VDC and still do max 30VDC.. (then 30A)

Same footprint would be nice for looks, but I can be creative :)

I can find solid state relays that can switch 60VDC, and add them.

While I don't like the idea of additional parts, that might work.
In my dictionary a SSR is made for millions of contacts in short time, and not continuous contact.
Looking at the heatsinks needed...
They produce quite some heat.

Is there a simpler solution?
I really hope so.

The contact of the relay is made with 5v.
Passing true voltage is 40-60v
As is the voltage during the start and release of the contact.
Voltage double, current 3%
Rated 300watt, 11w used.
It seems to be a magic barrier..
30VDC...
 

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