Li-thiiii-um.... continued.

[John in Santa Cruz]

Originally Posted by John in Santa Cruz

absootuvely for sure i'm gonna insulate those terminals, or put some sort of cover over tthe pair of the batts. 12V at 100A+ is no joke and can arc weld. The SOK came with rubber covers, but they only support a single wire, and 2 of my 4 battery terminals will have 2 x AWG 4 terminals on them as I'm paralleling two of them

Test fitting the batteries (using existing wiring for now).

so I plugged in my new PD4655L converter, and the SmartShunt is seeing ~13.5 volts and 45 amps over the stock 8 gauge battery wiring. I can feel that the wiring is getting a little warm (not hot anywhere), so definitely need to up-gauge it to #4.

I believe I'm going to run the batteries through a 100A ANL fuse right near them, so I may just do away with the thermal breakers entirely. I'm going to replace that annoying battery cut off switch with: https://www.amazon.com/dp/B07413JWLD

I'm also going to install one of those same cutoff switches under the bench to cut the solar panels feeding into the MPPT 100/30 solar controller, since everything says to disconnect PV before battery. Still not sure where I'm going to mount the plywood panel I put the MPPT and fuses and terminal connectors on. for now, leaning towards under that crossbar that supports the curbside bench aft of the batteries. I think I have a large enough scrap piece of 1/2:" Baltic Birch ply, and I have a cheap wood router table so I can use this to practice on.

[John in Santa Cruz]

so been charging them using the original 8 AWG... seeing 14.4V or so at the fuse panel in the power converter, but only seeing about 13.5V at the batteries, with a 45 amp or so charge rate. smartshunt says I've put 2.4kWH into the batts so far. So absotively for sure, I need to upgrade that wiring. i can tell that the 8 AWG wires are getting a little warm, not hot, just a little warm

thinking I might see if the batts will fit under the REAR bench, since my wife likes storing spare blankets and such under the more accessible side benches.

[Brian B-P]

Originally Posted by John in Santa Cruz

so been charging them using the original 8 AWG... seeing 14.4V or so at the fuse panel in the power converter, but only seeing about 13.5V at the batteries, with a 45 amp or so charge rate.

Impressive what just 0.02 ohms of resistance can do...

[BobG]

At the very beginning when I added a lithium battery and switched the OEM WFCO converter to lithium mode, I had a significant voltage drop of a little more than 4% from the converter to the battery. The converter was putting out 55 amps at 14.44 volts as specified for the charger. However, the battery was only seeing 13.8 volts. The wires and connectors got warm. I assume that this is not a good charging voltage but don't know because maybe as the battery charges the voltage will rise to 14.4 volts as the charging current drops. I didn't check.


In the end I did change out the whole electrical system to 24 volts. At that point I used the WFCO charger to top charge the batteries before connecting them in series. I changed the wiring to eliminate the large voltage drop before top charging them.

[John in Santa Cruz]

Originally Posted by Brian B-P

Impressive what just 0.02 ohms of resistance can do...

I'm kinda surprised, but I'm seeing almost 0.2V drop at ~45A between the Converter input to the fuse panel, and the battery connector on the fuse panel.

I should also mention in passing... this SOK battery is limtied to 50A charge, thats the same for the 100AH and the 206AH.. its hard wired into the BMS. My new power converter is rated at 55A, but I have two batteries in parallel, so I figure I'm good to go.

I'm still amazed at the 1 volt drop over a few feet of AWG8 cable, with a handful of connections. but that the FUSE panel is dropping a 1/10th volt up front, yeeesh.

the wire gauge from the converter to the fuse panel is really barely adequate for 55A.

soooo. planning to replace the battery cutoff switch with a better one. planning to bypass the thermal breakers in favor of a 100A ANL fuse near the batteries. planning on using AWG4 as much as I can for both + and ground in the path from the coverter to the batteries.

I still haven't even begun to sort out how I'm gonna deal with this bigass 360W 40V solar panel I got, and the Victron SmartSolar MPPT 100/30 controller I got to run it, but I'm sure when I get there, things will move along.

I'm *seriously* considering paying the local Marine Fiberglass Repair guru to do the panel mount for me. it might involve cutting and closing off the old fridge roof vent, since the Norcold N2175 really doesn't need that (its condensors are on the bottom, and it sucks air in from the inside, and blows it out the lower back, so the lower outside wall fridge vent should be more than sufficient)

[rubicon327]

Originally Posted by John in Santa Cruz

so been charging them using the original 8 AWG... seeing 14.4V or so at the fuse panel in the power converter, but only seeing about 13.5V at the batteries, with a 45 amp or so charge rate. smartshunt says I've put 2.4kWH into the batts so far. So absotively for sure, I need to upgrade that wiring. i can tell that the 8 AWG wires are getting a little warm, not hot, just a little warm

Maybe a high resistance connection somewhere? Sounds kinda high to start with. When I had original wiring…10AWG, thermal breaker inline and toggle disconnect switch I saw only 0.11V drop when bulk charging. After the changes (6AWG wiring, removed thermal breaker, new disconnect and new 60A Maxi fuse) it was 0.02V.

[John in Santa Cruz]

Originally Posted by rubicon327

Maybe a high resistance connection somewhere? Sounds kinda high to start with. When I had original wiring…10AWG, thermal breaker inline and toggle disconnect switch I saw only 0.11V drop when bulk charging. After the changes (6AWG wiring, removed thermal breaker, new disconnect and new 60A Maxi fuse) it was 0.02V.

40+ amps makes a high resistance out of anything. hah.

I'm seeing a couple 0.15V between the fuse panel converter output, and the battery connections on the same fuse panel, when the shunt is telling me 45 amps.

so definitely I need to upgrade the wire gauge. LFP bulk charge of 40=50 amps is a lot more than most lead-acid rigs ever see.

[rubicon327]

Originally Posted by John in Santa Cruz

40+ amps makes a high resistance out of anything. hah.

I'm seeing a couple 0.15V between the fuse panel converter output, and the battery connections on the same fuse panel, when the shunt is telling me 45 amps.

so definitely I need to upgrade the wire gauge. LFP bulk charge of 40=50 amps is a lot more than most lead-acid rigs ever see.

You just reminded me that I had lead acids at the time and no battery monitor. I had the PD charger in bulk but I don’t really know how many amps the batteries were even taking.

[BobG]

This is part of the reason I had 0.6V voltage drop when charging at 55 amps. Cables also got warm. I don't know why the 40 amp fuse in the charger didn't blow but it may have contributed to some of the voltage drop too.

[JeffreyG]

What you are running into is that 12V nominal operating voltage is ridiculous and ill-suited to actually delivering much power. As the industry is shifting to new battery technologies, what should happen is a shift also to 48V systems for the DC circuit. But that would require a whole new line of appliances, which the cost averse RV industry isn't going to easily jump into.


An industry with a vision would see their customers using solar and LiFeSO4 approaches to achieve huge power use off-grid, and would change operating voltage accordingly. Instead, were going to see RVs with 300 lbs of copper wire onboard trying to carry 300 amps.

[alanmalk]

Originally Posted by JeffreyG

What you are running into is that 12V nominal operating voltage is ridiculous and ill-suited to actually delivering much power.

...

I will second what JeffreyG is saying...

I'm old enough to remember when Volkswagen used a single 6V battery system. Those cars could barely start the engine and run lights, much less heaters and wipers that needed motors. 12 Volts was a bit better for the 20th century. But today's demands really require 24, or even better, 48 volts. Each time you double the voltage you can halve the amperage (in rough numbers). Maybe a bit more insulation is needed but the weight (and cost) of all that copper will go down significantly. And with MPPT, aka DC-DC conversion technology, the primary voltage hardly matters at the appliance itself. Anything with computer tech will be running internally at 5 volts or less anyway. Yes, there is a bit of conversion loss but in the end more power is saved by not heating wires.

Oh-well, I'm just ranting...

[rubicon327]

Originally Posted by JeffreyG

An industry with a vision would see their customers using solar and LiFeSO4 approaches to achieve huge power use off-grid, and would change operating voltage accordingly. Instead, were going to see RVs with 300 lbs of copper wire onboard trying to carry 300 amps.

Jeffrey: I completely agree that if starting from scratch a higher DC voltage makes sense if coupled with compatible appliances (fridge/microwave/air conditioner all DC). For those of us that are upgrading/retrofitting it seems to me that it is only significant if you have large DC loads and/or your inverter is far from the batteries and downsizing of the DC wiring results in significant money and weight savings. If the large loads are AC anyway and the inverter is right near the batteries like mine the length of wire doesn't seem to matter all that much. Seems to me the biggest limitation in this case is the maximum continuous discharge amperage allowable from a 12V lithium battery bank depending on the brand and BMS. Many appear limited to only 100A. Please correct me if my train of thought on this is wrong.

[oldwave]

Right the computer low voltage world has already embraced 48 volt Poe that powers devices over low gauge wiring, including fairly powerful radio transmitters for networks. Let’s hope the next generation appliances reflect this.

[Vermilye]

While I would have no complaints if the RV world switched to 48V as long as it included appliances & supporting devices, I have less than 4' total length of #2/0 wire between my batteries & the inverter. Changing the existing system to a 48V system would entail far more work & expense than the problem of the weight of the wire...

[alanmalk]

Originally Posted by Vermilye

...
Changing the existing system to a 48V system would entail far more work & expense than the problem of the weight of the wire...

As much as a higher voltage makes sense in the long run, the reality is the vast majority of us are going to have to live with our 12V systems for a long time. But quite a number of us have expressed an interest in switching to Lithium batteries which bring their own issues. One of which is the charging voltage is nominally around 14.6V. But some trailer electronics have problems apparently with anything over 13.8 (more or less). The Maxx fan seems to be one in particular.

It was purely a coincidence that in my email was a notice of a new addition at my favorite electronics shop. This $15 USD device will output a constant 12V up to 6 A when fed with anything from 8 to 30V - just what the Maxx fan needs, and maybe our LED fixtures and perhaps the Dometic electronics that seem prone to failure.

This is a link to Sparkfun (Boulder, CO).
https://www.sparkfun.com/products/18732

[JeffreyG]

Originally Posted by alanmalk

As much as a higher voltage makes sense in the long run, the reality is the vast majority of us are going to have to live with our 12V systems for a long time. But quite a number of us have expressed an interest in switching to Lithium batteries which bring their own issues.

I totally agree. One reason I ordered my E-19 with Li batteries was to get the Li capable convertor and the DC-DC setup already. But then I still went and messed with everthing.


To be clear, if you have a 12V trailer now (you do), I'm not suggesting switching to 48V would ever make sense.


But I'm suggesting that the industry should be pushing the appliance manufacturers to a 48V future standard so they can offer a trailer that is all 48V with Li batteries and solar in the future. Such a setup would be perfect with dry campers. Think about having everything at 48V including your solar array......losses are reduced, wire gauges can be reduced.


Basically the 12V architecture is archaic and suited to things like lights and sensors, not anything that uses real power.

[Brian B-P]

Originally Posted by JeffreyG

What you are running into is that 12V nominal operating voltage is ridiculous and ill-suited to actually delivering much power. As the industry is shifting to new battery technologies, what should happen is a shift also to 48V systems for the DC circuit. But that would require a whole new line of appliances, which the cost averse RV industry isn't going to easily jump into.


An industry with a vision would see their customers using solar and LiFeSO4 approaches to achieve huge power use off-grid, and would change operating voltage accordingly. Instead, were going to see RVs with 300 lbs of copper wire onboard trying to carry 300 amps.

There was a widely held expectation many years ago that the automotive industry would move to something like 42 volts, but it never happened. Instead, high-power systems (mostly hybrids) have gone to dedicated higher-voltage systems, leaving the power system for general use (lighting, entertainment, etc) at nominally 12 volts. In vehicles with a higher-voltage battery the air conditioner and electric heater are routinely powered from the higher-voltage system, which has both the advantage of lower current due to the higher voltage, and a much higher-capacity battery than the 12 volt system.

An RV could use the same approach, with a higher-voltage battery and corresponding inverter (and direct higher-voltage DC to select high-power equipment such as an air conditioner if desired), but still having a 12 volt system for all the little stuff (possibly with a small battery), and a DC-to-DC converter maintaining the 12 V system from the big battery.

[Brian B-P]

Originally Posted by alanmalk

As much as a higher voltage makes sense in the long run, the reality is the vast majority of us are going to have to live with our 12V systems for a long time. But quite a number of us have expressed an interest in switching to Lithium batteries which bring their own issues. One of which is the charging voltage is nominally around 14.6V. But some trailer electronics have problems apparently with anything over 13.8 (more or less). The Maxx fan seems to be one in particular.

... This $15 USD device will output a constant 12V up to 6 A when fed with anything from 8 to 30V - just what the Maxx fan needs, and maybe our LED fixtures and perhaps the Dometic electronics that seem prone to failure...

The DC-to-DC converter separates the battery voltage from the load voltage. If an RV owner can accept depending on a converter like this, then battery voltage can be chosen independently of the voltage needed by end devices - it could even be much higher than 30 volts.

[John in Santa Cruz]

the only high current DC lines in an RV tend to be short, converter -> battery, and optionally battery -> inverter, so really using a few feet of #4 isn't that big of a deal. even a compressor fridge is peak 7 amps, which is fine on 14 gauge.

higher power solar systems with MPPT controllers already use higher voltages, for example, the 360W panel I'm installing is max 40V PV and typically 36V, at 10 amps max, so 12 gauge is adequate, 10 gauge might have a slightly lower voltage drop but at 36V, even a 1 volt drop is less than a 3% loss. The MPPT output at a full 360 watts and 14V is about 25 amps, so those very short wires will be heavy gauge too.

higher current level DC-DC converters are pretty expensive, btw. and the cheaper ones aren't always that reliable

[BobG]

Equipment such as inverter/charger, solar charge controller, compressor refrigerator, etc run on 24 volts or 12 volts. Take for instance the MPPT 100-30; it can deliver 30 amps to the batteries at either 12 volts or 24 volts. However, if the system is 24 volts then it is capable of delivering twice the power(?) to the batteries. Same with an inverter/charger. For the same price, the MultiPlus can deliver 70 amps charging to the batteries at either 12 volts or 24 volts. Yes, a 24 volt battery in a 12 volt trailer will require a DC-DC converter and that will be an additional expense. There are also other issues to contend with.

Example of 24 vs 12 volts situation; in the case of John's solar panel, if he wants to add an additional 340 watt panel in the future, he will purchase an additional MPPT 100-30 controller if batteries are 12 volt but if the batteries are 24 volt then the MPPT controller he has will work with the 2 340 watt solar panels in series or in parallel.

Staying with 12 volts instead of 24 volts does make some things easier but it also has limits. I chose 24 volts and have wished at times I had not done so and other times I am glad I did.

I do like how 24V allows charging batteries twice as fast on shore power and using fewer solar charge controllers.