Converter charging amperage low?

[ARoamer]

craigav
Not sure if you missed it but his 12vdc wire run is 25'.
Yep, 8 gauge can carry 40A, but it would only be good for around 9-10' at 12vdc.
Can't really compare wire gauge capacity when it's 12vdc vs 120ac, 120ac will carry way more power in the same gauge wire than 12vdc. Your linked charts are geared to household 110vac and higher it appears.
>>>>fyi, your RV power cable is likely 10awg and can carry ~30 amps<<<<
30A @12 vdc = 360 watts
30A @110 vac=3600 watts
Running 3300 watts at 12VDC would be equal to 300 AMPS.

See Wire loss tables for 120ac/dc, 24vdc and 12vdc
https://www.solar-electric.com/learn...s-tables.html/

[craigav]

Thanks ARoamer, good discussion. A couple of points to share is that still an amp is an amp regardless of the voltage. That is why for example a typical 25a glass fuse can be used for 12v or 120v and will only blow if the amperage exceeds 25 amps (regardless of the voltage). You are very correct though that more power (watts) can be transmitted at higher voltages for the same amperage and conductor. This is the reason a power line can transfer a lot more power overall for such a small wire, as the voltage before a common power pole transformer for a house is often around 14k volts and even much higher up to ~500kv for cross country electric transmission lines.

In any case, the chart you shared is good guidance to follow and I don't disagree that 2awg would be better for the OP, however the chart has a predefined limit for a voltage loss of no more than 5% (which is considered a common percentage to stay under for a variety of reasons). In any case, while 5% is good guidance, you can certainly exceed that 5% without necessarily overloading the conductor.

So for example, at 25' with an 8awg copper conductor and at 14.6 volts source (converter) you could still carry 40a over that conductor but the difference here vs your chart is that doing this would cause a ~10% voltage drop (10.69% to be exact) which would result in having 13.04 volts at the battery vs the 14.6 at the converter. However, as the battery reached that voltage (13.04) the converter's charge circuit would start backing off the amps to maintain the 14.6v constant voltage at the converter and as the amps drop at the converter the calculation changes as the amperage drops. So for another example once the amp output of the converter drops to say 10 amps while still at 14.6v, then the line loss (voltage drops) will be below the 5% (2.67v drop) resulting in 14.21v at the battery. As the voltage of the battery reaches ~14.5 the output of the converter to the battery would be around 1~2 amps which results in almost no voltage drop and a fully charged lifepo4 battery.

So in summary, and based on what the OP stated "I know theyre almost full but that amperage is steady from 12.8V to about 13.6 then amperage tails off until 14.6V. It just never gets above about 10 amps even with a very low SOC (say 12.9V).". The converter along with the 8awg cable should be able to supply the battery with 40amps under this scenario (more or less depending on if the converter is also powering other things) as 40 amps over the 8awg 25' cable starting with 14.6v source and taking the hit for a 10.69% loss still results in 13.04v at the battery, and again as the battery voltage goes up the charge amperage goes down. Point being if only 10 amps is the most that ever gets to the battery, even when the battery voltage is 12.8 then somewhere along the circuit is more resistance than what an 8awg cable has which is why there is more resistance in the circuit somewhere (or possibly the amps and voltage readings are off).

Here is a fun calculator that matches your chart, keeping in mind that the chart maxes out at 5%, the calculator tells you what the line loss is though. For the settings since we are not dealing with a motor the Power Factor is 1 and I am not sure how they are using the "material of conduit" in the calculation as it doesn't change anything for the line loss, I suspect it is to warn you for too much heat in the conduit for longer and higher current runs than what I used.

~CA

Edit: I should have used the "Estimated Resistance" tab in the calculator instead of the "NEC data" tab for this case, the results are very close to each other in any case regardless of the tab chosen.

https://www.calculator.net/voltage-d...&y=0&ctype=nec

[DanNJanice]

Good discussion from ARoamer and CraigAV. I just wanted to illustrate the importance of wire size in 12VDC systems vs 120VAC systems.
First, the NEC's main purpose it to insure safe electrical systems are installed. Note, I did not say they worked...although if they are safe, they will usually work.

Now, regarding wire size, most 12V installers recommend a loss of not more than 2%. I don't really like using percentages like this because as was said earlier "amps is amps" The same amount of current flowing through the same size of wire will result in the same voltage drop. Note that I did not mention if it is a 12V or a 120V system. Because it doesn't matter when it comes to voltage drop across a wire.

Lets look at the previous example. With 40Amps flowing through a 8ga wire we have a voltage drop of 1.56V. So in a 12V system the final voltage would be 12.7-1.56=11.14V = Low enough that some devices, like invertors, might fault.

If the same wire and current is applied to 120VAC system we get
120 - 1.56 = 118.44 = I have never seen a 120V device that would not run on 118.44V.

Now lets look at battery charging. Below is a couple of circuits, the left is with a hypothetic perfect conductor with 0 ohms of resistance. I use that circuit to calculate the internal resistance of the battery. The circuit on the right is a practical circuit where I include the resistance of the 8ga 25ft run of wire.

As you can see, the result is pretty dramatic. We end up losing almost half of our possible charging current. Going from 40amps down to 20amps. This is because the interconnect wire resistance is almost as much as the battery's internal resistance. Will the circuit still fully charge, yes, as Craigav said when the battery's SOC increases the current though the wiring will decrease and the voltage drop will decrease as well. Will it reach its full 40amp maximum? Nope, not unless the convertor voltage is allowed to rise even higher than its 14.6V bulk charge setting.

In summary, wire size is very important when we start dealing with high currents in the 12V system. The interconnects are also critical, and an even more common source of problems.

[thenne1713]

Originally Posted by Fourkids&abeagle

Hello all,
My two Battleborn BB100s (12v) only charge at about 10-11 amps max. I have already upgraded the converter to a Progressive Dynamics 4045LIKA (45 amps max) set to the Li mode (constant 14.6V) and the batteries are monitored by a Victron BMV-712.

I’ve checked the batteries, they’re both good and hold a charge. My question is, if the charger is rated for 45 amps, and my trailer is rated for 30 amp service, why do my batteries only charge at 10-11 amps when plugged into shore power?

I’ve searched the forum but couldn’t find anything and I’ve left several messages with Battleborn with no return call yet. Any help you can provide is much appreciated!

The 45a is at 12VDC, and the 10-11a is chosen by charger voltage +/- to prevent overheating battery. The 30a is at 120VAC

[Fourkids&abeagle]

OP here, this has all been super helpful. I got the trailer today and did some more research, realizing like thene1713 says, I was mixing 30 amps max of 110v AC with the DC readings at the battery. So, now I understand why it says it takes in max 30 amps but can output max of 45 amps. Never understood that until now.

Also, I checked the wiring behind the converter and found the DC positive 8awg wire connected to a 14-or 16awg wire right at the back of the converter for some reason. So I connected it straight to the battery pos terminal on the main board per the manual, and I instantly saw 18amps going in to the battery. So that's a good sign.

Also, for some reason the 8awg negative (black) was split at the junction box into three 10awg wires - one to the breaks, one to the 7-pin, and one to the converter. So that means the circuit is actually running on 10awg.

So I checked the calculator that ARoamer linked to earlier, and sure enough if you put in 30 feet of 10-awg DC, the voltage drop is 1.109v. So, I did the math...14.6v output at the converter minus 1.109 is 13.49v. Then I touched the converter wires at the battery and they read...13.47v!! So I think I've found the root cause, the 8awg positive and the 10awg negative are too resistant and there's too much voltage drop to get to 45 amps DC charging.

So...my 2awg wire shows up (2x40') tomorrow. My plan is to crimp a lug onto one end of each pos and neg wire and attach the pos to the shunt, then the battery, and attach the neg to the battery, then run both wires straight through a door or window to the terminals on the converter. Then I think THAT should show a jump in amperage and voltage. Once that's confirmed, I'll do the dirty work of running it the entire length of the RV alongside the other wires.

Thanks guys! Very excited for later this week when I can get to the trailer again. Will be a Moment of Truth time, for sure.

[Fourkids&abeagle]

DanNJanice - thanks for the depiction, really helps me visualise and understand the effect of resistance and corresponding voltage/amperage drop.

[Fourkids&abeagle]

Ok so the 2awg wires showed up Yesterday so I was excited to try it…and then immediately realized that the PD4045 connections can’t nearly fit 2awg. Is there a way around this? I’ll call them Monday but it looks like maybe 6awg is max and then not sure if that’s worth time/effort since it’s 8awg now.

Another update-when I got to the trailer I realized I’d accidentally left the disconnect on, so the Battleborns were dead. When I plugged into shore power with existing connections, I got 30 amps! So now I’m thinking the change I made of plugging the 8awg battery cable straight into the connection on the converter and bypassing the 10awg that comes with the converter is what made the big change. When the batteries were almost full I got 18 amps into them after making that change. Prior to that change, max amps were 10-12. All that to stay I’ll do some more testing but may end up keeping what I’ve got now that I have an 8awg connection instead of the original 10awg.

[craigav]

What is the picture on the left showing? Is that the 2awg or the 8awg cable? In any case, it looks very dangerous and hopefully you don't leave it like that. Strands of the cable on the positive appear to be dangerously close to the ground connection and will likely short out with time if left like that. You also have way too much insulation pulled back.

I don't like using "reducers" but in this case that is what I recommend. Not necessarily this one, but I share this to give you the idea of what I am talking about. You need to match up the wire size to the connector size accordingly. Also, I am very familiar with electronics and related systems, while 2awg would be best, I still have no concerns with 8awg for your setup. In any case, you need a clean neat connection and something like this could be your friend. ~CA

https://www.ebay.com/itm/19309527279...sAAOSwGmddeAPq

[thenne1713]

First. YOU are MIXING 10a/20a at 120vac vs 10a/ 20a at 12vdc, but how long could YOU HOLD an old 100-120-watt incandescent battery or electric heating element? Heat is a battery's enemy, and esp. LEAD-ACID will BOIL DRY in short order if left at HIGH charge too long. SHORT Periods of HIGH charge/ BOIL are good to prevent sulfation in Lead-Acid. (I assume) LI-ION have similar issues. We know from POWER TOOLS that they auto-disconnect thermal switches INTERNAL to prevent damage, (fire risk) whether is use/ discharge mode, or charge mode. Remember all the RECALLS on the skateboards/ toys?

[Fourkids&abeagle]

[QUOTE=craigav;992096]What is the picture on the left showing? Is that the 2awg or the 8awg cable? In any case, it looks very dangerous and hopefully you don't leave it like that. Strands of the cable on the positive appear to be dangerously close to the ground connection and will likely short out with time if left like that. You also have way too much insulation pulled back.

The pic is showing the 2awg - I probably should've said I didn't connect that to the battery, I was only trying to show visually how much smaller the connections are than the 2awg.

Thanks for the advice about the reducer and about the 8awg. I'll probably just comb through all the factory connections to the battery protector and the fuses at the front and make sure they're all clean and tight. Guess I was just surprised that the PD4045 doesn't have any larger connections.

Thanks again for all the great info to everyone that has posted, I am much smarter on electricity and the associated wiring than I was before.

[01tundra]

Originally Posted by Fourkids&abeagle

Ok so the 2awg wires showed up Yesterday so I was excited to try it…and then immediately realized that the PD4045 connections can’t nearly fit 2awg. Is there a way around this? I’ll call them Monday but it looks like maybe 6awg is max and then not sure if that’s worth time/effort since it’s 8awg now.

Another update-when I got to the trailer I realized I’d accidentally left the disconnect on, so the Battleborns were dead. When I plugged into shore power with existing connections, I got 30 amps! So now I’m thinking the change I made of plugging the 8awg battery cable straight into the connection on the converter and bypassing the 10awg that comes with the converter is what made the big change. When the batteries were almost full I got 18 amps into them after making that change. Prior to that change, max amps were 10-12. All that to stay I’ll do some more testing but may end up keeping what I’ve got now that I have an 8awg connection instead of the original 10awg.

You can set power posts behind the power center and then run short, smaller wire between the posts and converter. I had to do this when I was still using our factory WFCO converter and still had to do it on our Progressive converter (1/0 to the power posts and then about 8" of 2 AWG between the posts and converter). I used power posts often for this purpose (converter, solar controller, DC-DC charger, etc.).

I always terminate with quality copper tinned crimp lugs and good adhesive heat shrink.

https://www.amazon.com/Blue-Sea-Syst...9733114&sr=8-3

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Fourkids&abeagle]

More great stuff, Tundra. The pics and links are awesome. Thank you!

I talked to PD just now and they said 4awg will fit. So I just ordered wire and lugs, and have the same crimping tool you linked to. When the 4awg wire gets here I’ll try it again just running straight from converter to shunt to batteries and back. Might take me a couple of weeks to get back to the RV but I’ll post back when I do.

[Fourkids&abeagle]

UPDATE: I got 45 amps!! The 4awg wire did the trick!! Now for the routing and fuse installation…but I got it fixed! Man I’m so excited about this. I boondock a lot at National and State Parks out west, so now my battery will charge with twice the amperage that it used to. THANK YOU SO MUCH!!

(Apparently in my excitement I forgot to take a screenshot of the BMV-712 readout…rookie mistake)