Wiring and fusing 10 x 100 watt panels

[bri2k]

I'm starting to piece together the details of how I'm going to wire the panels on my van and I'd like to hear your thoughts. Here's what I'm looking at hardware wise:

• 10 x 100watt HQST panels (Panel sticker)
• Electrodacus BMS with 2 x DSSR20
• 24v LFP battery

Based on my understanding of the Electrodacus and the DSSR20s, I need the panels to be in 2S to output the appropriate voltage for a 24v lfp battery. The DSSR20s are limited to 20A each so that leaves me with one group of panels is 2S2P and the other in 2S3P. If I'm reading the panel specs correctly, they're rated for 15A current but have an ISC of 5.28A. That being the case, I assume I don't need a fuse between the strings on the 2S2P group, right? On the 2S3P group, maybe not also? If one string shorts that leaves two strings pushing ~10.56 amps, which is under the 15A rating of the panel, right? The DSSR20s do act as diodes and I will have fuses/breakers after the junctions. Am I on the right track?

Thanks

 

[gnubie]

You are right, there is no technical need for fuses on the 2s2p array, but you should have fuses in the 2s3p array. The fuses go between each string and the common + (typically) wire.

15A is the maximum permissible fuse so the panel can handle being reverse fed that much current total (this total probably includes its own internal power generation but I've never looked into that) but at that current you can expect things to be getting quite hot. Ideally you want to fuse below the maximum but above Isc x 1.25, around 7A. Remember that your fuse's rating degrades with heat so if they are exposed to heating from say the sun you want to overrate them a bit. Quality fuses will give you a temperature derate in their datasheet.

 

[Hedges]

1 kW of panels. At what point does MPPT start looking better than PWM?
"2S appropriate voltage for 24V lfp battery" - two of these batteries has 41Vmp, seems like you may lose some potential power with PWM.
Is your application fixed, or mobile? Temperature [range]?

 

[gnubie]

Now you've done it. You've called the SBMS a PWM controller! Based on past experience this should result in your being burned alive.

MPPT would do a better job, , but the losses might be acceptable to him.

 

[Hedges]

Oops, is that a diversion regulator?

https://electrodacus.com/DSSR20/DSSR20.pdf

Not me, I'm safely here playing keyboard warrior. It's bri2k who'll be burned alive if I give him bum advice.
?

Does he have a dump load? And do those need to always accept that 1 kW if batteries don't need it? Sounds like a pretty good size space heater without an over-temperature switch.

 

[bri2k]

Lol. You guys are hilarious.

The panels are going on a van.

My understanding is that since LFP batteries can pretty much handle whatever current the panels can throw at them and they don't need an adsorption or float stage so there's no reason to mess with PWM. The DSSR20s are just acting as a relay to connect the panels straight to the battery until they reach full charge voltage.

I did not get the DSSR20s with diversion, just the regular ones. I thought about getting diversion to heat water in a small water heater but decided against the extra complication.

Yes, MPPT might be more efficient but since I'm going with the SMBS0 anyway I figured it can't hurt to try the DSSR20s. If they work, great. If they don't I'm out $50 and I learned something.