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SSR testing

Craig said:
Yes I figured that would be the case. That everyone is different.

Ok so I need to compare relays at about 200 amps I think I can do that.

My LTO bank is 70Ah so not only will I be testing realys I will be testing the Cells at a 3C rate. Problem is that only gives me 20 minutes. But I think it's enough until my machinist gets me my new bus bars for my 120Ah system. Giving me a total of 190 Ah.
Click to expand...
When communicating with the supplier, I'd forward the idea to them, that with heavier DC loads like we have in Storage Systems we use Cabling from 4/0 and smaller, that typically the lugs are 3/8 - 9.5mm (10mm) or 5/8 - 16mm I'm not sure about the euro sizing. The Battery Cable lugs have got to fit well and have enough surface contact.
 
@Craig and others.
I am just working on the documentation related to the Delay Board for Chargery BMS' and it's application / configuration.
As part of that, I have ordered a few components in order to accommodate a pre-charge circuit using the "small relay" port on the delay board.
The "Small Relay" only has to be an automotive 4 pin ISO mini relay that is N.O. (Normally Open) to trigger the pre-charge.

Items required: Fuse, Fuse Holder, Resistor (200 Ohm) per delay board (note, I am running with 24VDC)
- For the Resistors I kept with 200 OHM as KISS is to be applied.
- Quick Resistor info:
--- 12V 200 Ohm = 1 Watt / 60ma
--- 24V 200 Ohm = 5Watt / 120ma
--- 48V 200 Ohm = 15Watt / 240ma

Parts from Digi-key (They ship worldwide) (this is what I ordered for my application)
-- TE Connectivity Passive Product 200 Ohms ±5% 10W Wirewound Chassis Mount Resistor
-- Little Fuse 0977010.MXP (10A 500V AC 450V DC Fuse Cartridge, Ceramic Holder 5mm x 20mm)
-- Schurter Inc. FUSE BLOCK CART 600V 10A CHASSIS Fuse Block 10A 600V 1 Circuit Cartridge Chassis Mount

IF you need to figure out resistor info & other valuable info:
Resistor Power Rating Calculator

Resistor Power Rating Calculator | Amplified Parts

www.amplifiedparts.com www.amplifiedparts.com

Hope it helps,
Steve

PS: Quick reference on the "Small Relays" for those who need a helping hand with them.

Automotive Relay Guide | 12 Volt Planet

Read our guide to relays found in vehicle electrical systems. How they work, why they're used and some example applications
www.12voltplanet.co.uk
 
You really need one value per voltage, you can't just use 200 Ohms for the three as for the 24 and 12 V it'll take forever to precharge the caps, and for the 12 V the current is so low you might not precharge them even after a few minutes.

Also if the resistor is of the metal body with screw holes type then it can't dissipate the rated power on its own, it must be placed on a heatsink. I recommend the ceramic type resistors who can dissipate the rated power as-is.

For 48 V I recommend two 240 Ohms 10 W 5 % resistors in parallel (0.4 A total precharge current).

For 24 V I recommend two 16 Ohms 10 W 5 % resistors in series (0.75 A total precharge current).

For 12 V I recommend one 16 Ohms 10 W 5 % resistor (0.75 A total precharge current). You can put two of them in parallel if you want to double the precharge current.

Why a 10 A fuse? a 1 or 2 A fuse would be plenty enough and safer.

NB: for the more adventurous members you can use a lower value resistor if you add a PTC in series https://diysolarforum.com/threads/how-can-i-make-this-600w-safer.4389/page-4#post-46072

NB²: be careful about the links as you linked the manufacturers instead of the products (it happens when you click on the manufacturer instead of the reference in the search results, that's a bit of a PITA, I know...).
 
UPDATE.

I have placed 180 Amp loads for 15-20 minutes on the 500A SSR the relay itself with the heatsink performs well. The Terminals do not!
The screws heat up to about 180F after 15 minutes. The relay itself stays well under 100F

The manufacturer is making me some new ones with larger terminals 3x the surface area to try. I think it will definitely help but how much will be determined in about 3 weeks when I get the new custom ones.

If you have moderate loads less than 75 Amps I think these will work well as they are while I am waiting for new ones I will preform a long test at 50 Amps to see how it works. Will do test on 200A SSR since they are about 1/2 the cost

I have one set up full time on my system with moderate loads 5-20 amps and it does not get warm anywhere.
 
So 30 W losses @ 150 A, not great but acceptable, especially in a small package like that, thanks for the numbers ;)
 
It should be a lot lower, like 1/10 of that.

The SSR with better terminals should be lower too as apparently a lot is wasted here and not in the mosfets with the actual design.

0.8 % but at what voltage? because on a 24 V system it'll be half the percentage of a 12V system for example.
 
Great testing. It will be very interesting to see what the larger contacts do. By the time you are done we will have a good idea of how much to derate them. Useful work!
 
So after 2 weeks of normal usage with my 200Amp SSR everything is working well. Normal usage is about an average high of 50amps with a constant load of about 10A. I mainly run lights charge my batteries for testing and the occasional power tool and 3 or 4 raspberry pi and a chest freezer.
 
Craig said:
Well I think we may have a winner!

Tested this

View attachment 9352


After 15 minutes at 50 Amps Temperature was only 71 Degrees F. Voltage drop was 0.1 V and Controll load draw at 12Volts was 0.34 Amp

This 240 Amp relay will be about $40.00 including the beefy heat sink ($6.00)
The 500 Amp relay I will test Tomorrow but It is quite a bit more expensive $100 including heat Sink. It has max voltage of 75Volts

I do not have a spec sheet as this is what distributor recommended and sent me to try.
Click to expand...
300mohm!
They can do much better. I wonder what all the other components potted in the SSR are for, stability and LED?
Here is a FET with VDSS=100V, 50A Rdson=5mohm.
https://www.infineon.com/dgdl/irfh7185pbf.pdf?fileId=5546d462533600a40153561ee0b11ee1
 
Craig said:
I never updated this thread. My meter was off the actual load was .0013 at 12Volts
Click to expand...
Oh! Now that is a winner.
OK, Now do you have any BMS8T-300s left, 300A shunts and 250A (or 500A) SSRs? I suspect the FET is the same, only the heatsink size is different.
I only need the SSR to cut out the Charger at Low Temp. I have programmable over/under voltage control on the charger MPPT to prevent that.
Ironically, I am the I/C product and test Engineer for the MC33772b and the MC33771 BMS cell balancing ICs but I don't have knowledge about how my I/Cs are used in the application. This is fun.
 
r11066 said:
Oh! Now that is a winner.
OK, Now do you have any BMS8T-300s left, 300A shunts and 250A (or 500A) SSRs? I suspect the FET is the same, only the heatsink size is different.
I only need the SSR to cut out the Charger at Low Temp. I have programmable over/under voltage control on the charger MPPT to prevent that.
Ironically, I am the I/C product and test Engineer for the MC33772b and the MC33771 BMS cell balancing ICs but I don't have knowledge about how my I/Cs are used in the application. This is fun.
Click to expand...
I have the *t's but do not have the relays just yet as we are testing new ones.

But you cant go dropping BMS parts with further elaboration. What are these things I looked them and they seem interesting especially paired with a MCU please post here or pm me with info. Thanks.
 
Folks,
I am a bit late to the party.... and have a question: Has anyone looked into magnetic latching relays?
These take a pulse on the coil to turn it on and another pulse to turn it off. You don't have to keep the coils energized.

These are usually controlled one of two ways:
1) Reversible coil: Positive pulse turns on, negative pulse turns off.
2) Dual coil: Pulse on one coil turns on Pulse on other coil turns off.
 
Ideally there would be a custom delay board for it. Failing that you can use small SSRs to build the on-off logic. I did a design for it once but can't seem to find it right now.
 
I found it.
This uses a Magnetic Latching relay that uses a Positive - Negative pulse.

1587848885093.png
Notes:
  • If you want an explanation on how it works, let me know.
  • I specify the Weidmuller 1127150000 solid state relay for the control logic because I have worked with them before. Any small relay can be used for the control Logic.
  • Relay 3 needs to accept the system nominal voltage. The Weidmuller 1127150000 is a 12V relay but 24 and 48 V versions are available.
  • Some latching relays come with the flyback diodes across the coil. I would not trust this circuit without them either built in or added.
  • Some latching relays come with fuses built in (as shown above), Others don't
If the Latching relay has an auxiliary contact, it can be done like this: (I like this better)

Edit: Added coil fuse to following diagram:
1588462743411.png
Edit: Added the following theory of operation for the second circuit.


Turn On sequence
  1. The circuit as shown is the starting point with everything off.
    Note that in this state, both sides of relay 2 coil are hooked to the positive, so nothing will happen.
  2. The Chargery energizes the signal, causing relay 1 to turn on, connecting pin 1 of the coil of relay 2 to negative.
  3. Since pin 2 of the coil of Relay 2 is already connected to positive, the coild is energized in a 'positive' direction, energizing the load and flipping the auxiliary contact to B, connecting relay 2 contact to negative.
  4. When auxilary contact on relay 2 flipped to negative, both sides of the coil of relay 2 is connected to negative and the coil is de-energized. However, since relay 2 is a bi-stable relay, it does not change state.
At this point relay 2 is on but not drawing any current on the coil. Relay 1 is on but only drawing about 20mA.

Turn off sequence
  1. The initial condition is that relay 1 is on and the bi-stable relay is on but the coil is not energized because both sides of the coil are connected to negative.
  2. The Chargery turns off the relay signal so relay 1 switches state, connecting the pin 1 of the coil of relay 2 to positive.
  3. Relay two now has an 'Negative' energized coil with Positive on Pin 1 and Negative on Pin 2. This causes the relay to turn off, de-energizing the load and flipping the auxiliary contact to “A” (Positive).
  4. Both sides of the relay 2 coil are now connected to Positive so the coil is de-energized but since it is a bi-stable relay, it does not change.
 
Last edited:
Wow. Very Interesting Topic with 8 * 280 Ah LiFePO4s on way, and a Chargery BMS8T in hand. After Will's recent video clips on that Chargery BMS; with highlight on temp generated and watts used by those relay, I am all eyes n ears on what is new with relay options. I would highly value seeing a low watt use relay that could handle 24vdc or 48vdc with 250 amps. with longevity potential. ;+)
 
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