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diy solar

Expected energy losses through long runs?

LVLAaron

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Jul 16, 2021
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I have a brand new 15 foot camper. Came with 2 lead batteries. I build a lifepo4 pack and put it in the rear compartment of the camper. I ran 2GA welding wire from the front of the camper where the main 100amp breaker is located and all the positive leads tie together for batteries, inverters, chargers, etc.

The factory "converter" would only charge maybe 10amps, usually less, not awesome.

So I decided to put my AIMS 75amp charger in (https://www.aimscorp.net/ac-convert...art-charger-75-amps-listed-to-ul-458-csa.html) This charger works awesome on my bench. I charge my packs with a 4 foot lead of 2GA welding wire with an anderson power pole on the end. When charging the BMS shows 75 amps going in. Great.


I put the AIMS unit in my camper. 120v plug into a circuit that only operates on shore power.

I attached the output of the AIMS unit into the factory inverter lugs. (It has 2x pos and 2x neg lugs for 2ga wire)


So from the AIMS to the battery, there is a solid run of 2GA wire, 16-18 feet in total lenth. All of the connections I made are solid, hydraulic crimped with solid copper connectors. At the battery end of the new cable run, I have a Victron Shunt, and a Blue Sea 150amp fuse, but again, very solid connections.

The only connection that might be questionable now that I think about it, is where the main negative from my aftermarket run is bolted to the factory 2ga wire (factory connector has a huge binding post hole, and the binding post it's connected to is 1/4 inch maybe).



On to my problem.

The battery is only charging at ~34 amps. This unit has a dial that adjusts output, if I turn it all the way down it outputs 20 amps, and that is what the battery will charge at. On max it's the 34 mentioned amps.

As I am testing this, there are no other loads on the system. Verified by powering off the aims unit and checking the BMS.



Should I expect these kinds of losses over this distance?

I really want maximum charge speed, so when I do need to charge it happens as quickly as possible. I could move the AIMS unit closer, but it would be a hassle to wire a new mains circuit.
 
Confirm you are not at the absorption voltage. If you are, it doesn't matter how much current you can throw at the battery - it won't take any more than it can to hold the absorption voltage.

Confirm that all your cell interconnects are properly torqued.

Measure voltage at the charger.

Measure voltage at the battery.

The difference is your voltage drop.
 
Took the battery down to 50 percent overnight, so there should be no problem charging at full rate.



With all power off
Voltage @ Charger terminals:13.01
Voltage 6 feet from battery, Shunt & Fuse connection13.04
Voltage @ Battery13.07

With 25amp load
Voltage @ Charger terminals:12.5
Voltage 6 feet from battery, Shunt & Fuse connection12.78
Voltage @ Battery12.87

No loads, charging (45amps)

Voltage @ Charger terminals:14.08
Voltage 6 feet from battery, Shunt & Fuse connection13.65
Voltage @ Battery13.5
 
The charger is set to a Gel Profile (14.0V Bulk / 13.7 Float) - So I can now see why it has reduced output amps. I switched it to LifePo4 (14.4 Bulk / 14.4 Float) and the battery input amps were 65-66.

Guess I need to get it closer to the battery if I want the maximum output. :/
 
This is good to know. I have the same Aims Converter and am waiting to install it in my RV for my 24 volt upgrade. I estimate 8’ one way of 2 gauge wire to the busbar, and then another 3’ one way of 4/0 to the battery.
 
A lot of voltage drop there. Too small of wire? Poor crimps on cable? Dirty connections? If you measure mV across connections while charging at your highest amperes you can quickly find the resistance.
 
This voltage loss calculator says you should have 13.97 at before the shunt with 45 amps charging. That means .35 volts disappears somewhere. Not sure what to make of that.

 
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Every single item, lug, terminal, bolt, connection adds resistance and subsequently a bit of voltage drop. Then add wire length and that can also result in drop but the lurking gotcha in this... Now all wire is equal and especially not welding wire. High Quality Pure Copper Fine wire can deliver a lot more amps @ a set gauge than the more coarse stuff and especially those with blended copper. You'd be shocked at what some sell as welding wire. I would not have used anything less than 1 Gauge Fine Copper Welding wire and I only use Royal Excelene by Southwire.

Southwire specs: http://www.industrial.southwire.com/en/search_products/?search_field=Royal+EXCELENE

Good Supplier:
https://www.wireandsupply.com/searc...g=Y&sort=7&search=1+awg&show=30&page=1&cat=22

Now the GOTCHA !
The voltage at the Battery Terminals is the important one. ANY SCC or "Charger" MUST know what the voltage is & be corrected for any differential during charging, even a 1/2 Volt off can result in trouble ! So if you want to charge to 14.0V (at batt) and you read 13.5V at the Charge Source (when batt @ 14V) you will hit a nasty wall of undercharging and will have off readings. So ou will have to compensate / correct so that you get what you need/want at the battery terminals during charge.
GOTCHA - 2.
Differentials always appear differently between charge & discharge. Any inverter or device that draws will have cutoff points for Low Voltage. LFP cannot go below 2.500V per cell and generally best NOT to go below 2.750 (with the exception of a momentary load sag). So now you will have to also correct for what the voltage is @ BATT and @ Inverter so that when the battery reaches 11.0 that the inverter is not reading 11.5 or 10.5.
So again, depending on your hardware you may have to Fudge the numbers to correct for that or if your equipment has offset settings, typically Tier-1 products do, value gear never does, Aims = Value Gear.

Hope it helps, Good Luck.
 
I'm using temco wire, which gets recommended often. It seems like very nice stuff.

This morning, I moved where the converter/charger lives. I added an outlet and attached the charger here:
h5D8j2c7sx.png


This cuts out about 12 feet and 4 connections between the battery and charger. Some of that 12 feet is factory 2ga which has less than idea crimps and is probably not actually 2ga wire.

This change got my amps going into the battery up to ~71

I'm happy with this.
 
I wonder how many amps others with this converter see. It will be a few weeks before I get it.

My AIMS converter was delivered bad from AIMs and I’m waiting on a replacement. They did not have them in stock and it is back ordered.
 
I wonder how many amps others with this converter see. It will be a few weeks before I get it.

My AIMS converter was delivered bad from AIMs and I’m waiting on a replacement. They did not have them in stock and it is back ordered.

I've been using it on my bench with ~3 feet of cable attached. Full 75 amps. It's a great charger.
 
In addition to the above exercise you conducted, you can measure voltage drop across a component/conductor and determine it's contribution to the voltage drop, e.g., sometimes fuses increase resistance before they fail. Under the prior load/charge scenario, you could measure voltage between the fuse block terminals and see its voltage drop.
 
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