shunt upgrade- high amps draw by the Rideon shunts

[Peter Kuczynski]

Hi everyone,

I upgraded both my shunts from the cheap chinese 200A/75mv to Rideon 500A/50mv shunts.

On my old Chinese shunts, the ohm setting was calculated 75ma / 200a = .375. The Electrodacus showed a .21 battery draw, which Dacien explained as what the electrodacus draws by itself.

I swapped in the Rideaon shunts, and followed the same math. .50mv / 500A = .1 But now the Electrodacus says its drawing 1.4 Amps . Nothing else has changed.

Nothing is plugged into the batteries. Power is going from the batteries direct to the shunts. So whats going on ? Is my math wrong ?

The last couple of pictures how the Electrodacus by itself, no power is passing thru the shunts, and then with power passing thru the shunts.

Peter

[Peter Kuczynski]

LOL, I read the Shunt calibration recommendation in another post. I turned off the SBMS waited a minute, powered in on, and were bak at the origional current draw, .02.

Sorry for cluttering up these posts with yet another shunt question, clearly im still learning.

But please check my math regardless. Ive not do any offsets either.

My entire rig is meant to be mobile, so i set the batteries in th larger bottom insulated box, and the electronics are in the top, inverter and such, still to be wired in.

This will all plug into a breaker box on the wall of my Schoolie bus once I set that up.

Peter

[Dacian Todea]

Peter,

Yes your math for current shunt's is correct.

No worry other people will want to read this and see the photos.

Your cells seems to be charged above the default limits. Best guess is that you have not connected the EXT IO4 to control the charger.

[Peter Kuczynski]

Correct, No controllable charger.

I am currently working on wiring up the DC side, stepping down from 24 to 12 into a small 12v fuse pane.l Then I'll move to the DSSR20's. I have no clue yet how to wire those, so ill check the docs first before I bother anyone.

No clue yet on which panels or how to wire then either. I've read you mentions to go w 60 cell, in parallel ? As much wattage as I can find, total 4 panels.

Im still on the fence for which Inverter to go with.

The Cotek SP 1500, more then likely OR the ever popular Victron Pheonix 24 .

I am using a bench charger for now, same one I top balanced with. Totally not controllable. If you have a charger recommendation, I'm all ears, the Victron's are out of my price range at $1100 or so. Id rather do this project on the cheap or DIY as much as possible.

BTW, thanks for the card board box idea, I love it!

Thanks Dacian!

[Bernd]

Hi Peter,

take care of all the details and only work on the system if you are in "relaxed mode". I had some learnings.... Also raise one question more here upfront in the forum, than do the learning on your own.

Regarding inverter:

I will need to replace my inverter and also look at victron phoenix smart 24V/5000 but also concider Steca at the moment. I think the 5000 modell is rather new....

Andy from the off-grid-garage is currently installing a victron inverter and will wait for his review on youtube.

Regarding DSSR20: I got it working, but even after a few months, it seems it didn´t understand all parts correct esp. regarding diversion and DEXT16 connections.

[Dacian Todea]

Peter,

60 cell panels are the most common and made with 6" cells either full size or more recently half cut cells so there are 120 half cells (but connected as two groups of 60 half cut cells in series about the same as having two parallel panels in one and so better for shading). This 60 cell panels are usually rated from 290W up to around 340W depending on how efficient the cells are.

Cotek is not a bad choice as they are great inverters and they have the remote ON/OFF port so you do not need to do any modifications it can directly accept the EXT IO3 from SBMS0

The cardboard I used just because it was easy for me to cut and demonstrate how the SBMS0 can be installed and it is only good for a temporary install/test.

[Peter Kuczynski]

Thanks Dacian and Bernd,

I will go with 60 cell panels, most likely  4, two DSSR20's, in parallel, on the roof of the bus.

I will most likely go with the Cotek pictured here as well. I am use 4G wiring on the supply side as the inverter is 1500W. Is this adequate? I dont expect to use anything larger then a hair drier once in a while. We probably wont be using a micro wave even. So just a small fridge, 2, diesel heaters, which in my experience draw 8 watts each when running, led lights, laptops, yeah.

The DC wiring is complete, pictured is the 40watt dc 24 to 12 converter, and a 50A breaker on the pos side of the power supply to the converter.

My next task is to order the inverter and wire it up, as well as start wiring up the DSSR20's. I have a couple of questions on those.

1. Is this the correct documentation: https://electrodacus.com/DSSR20/DSSR20.pdf

2. What is "Diversion", when is it used, and for what purpose. Would I ever need it on a schoolie bus roof, I'm guessing it doesnt fit my use case.

and I am taking my time doing all this, the North is frozen over completely so nothing else to do but work on the solar box. Today Ive seen the first signs of snow melt. So maybe by this weekend if I can dig a trail to the bus I can do some work inside.

Cheers!

PEter

[Dacian Todea]

1550W / 24V = 62A so maybe 70A max continues as efficiency of the inverter also need to be considered so yes even 6AWG with at least 90C insulation can handle this current but is not bad to have thicker wire and as short as possible as it will prolong the life of the inverter input capacitors.

1. Yes that is the correct manual for the DSSR20 v04d

2. Maybe you do not need the diversion. When battery is fully charged the panels can be diverted to some sort of restive load like a water heater or a space heater allowing you to use excess unused PV energy for something like that.

I also need to clean my road of snow but is fairly heavy and frozen I will prefer for it to melt.

[Peter Kuczynski]

RE:  Maybe you do not need the diversion.

"When battery is fully charged the panels can be diverted to some sort of restive load like a water heater or a space heater allowing you to use excess unused PV energy for something like that."

I am still trying to figure out how to wire up my 2 DSSR20 without diversion. I understand I need to buy a 1-10 ohm resistor, then solder that  to one end of a 22g wire, [I will just use a strand from a cat-6 cable] then connect that FROM  a  Bat + 24v power source TO the DSSR20 BATT gray tinni connection. THEN add a jumper from there TO the other DSSR20 BATT tinni terminal.

If all that makes sense.

I had no idea what diversion was when I purchased these DSSR20, now I do. So Question: can I use my current DSSR20's to also charge my dual bus starter batteries? They are standard parallel 100ah batteries like in any other school bus. The idea is, when the bus is sitting somewhere for a  week or two, it would be nice to keep them topped off at 14.4 volts.

Do I  need to buy the 2 DSSR20 with diversion and the DEXT16 to make this happen.

Thanks Dacian, I searched the forums and couldn't locate a use case similar to this.

Peter

[Dacian Todea]

Peter,

You need a 1KOhm resistor not 1Ohm that is 1000x difference.

That resistor as clearly shown in manual page 7 connects to battery+ on one side and EXT IO4+ on the other side then EXT IO4- is what will connect to DSSR20 Batt grey connector and from there you can have another wire going to the next DSSR20 if you have more of them.

Yes you can use the DSSR20 with diversion + DEXT16 to charge a Lead Acid battery after the main LiFePO4 is fully charged by connecting the Diversion output (Heat+) to a Lead Acid solar charger PV input.

So you need a Lead Acid solar charger as the DSSR20 Heat+ output is basically just the PV panels positive wire directly thus that will need to connect to PV+ input on a Lead Acid solar charger.

[Peter Kuczynski]

Thank you Dacian,

I understand.