What can limit charge output from the converter?

[eatSleepWoof]

My OEM converter is rated for 55a output, but I've never seen more than about 10a actually going to the batteries. (As per my negative shunt.)

On a regular 15a, 120v (residential) circuit, I should have up to ~150a at 12v. I would imagine this would allow the converter to send plenty more to the battery (than the current ~10a), but that's definitely not happening.

Am I missing something, or is there likely to be a bottleneck of some sort? If the latter, what could it be? Undersized wiring? Would getting the "full" output be as simple as upsizing the gauge of the wires?

My use case is primarily to quickly re-charge the trailer using a (recently purchased) generator, that outputs 20a. I've got proper wiring running from the generator to the trailer (rated for >= 20a), but am still only seeing the same amount of charge that I also see when plugged in at home.

I know some folks install a second converter with heavy-gauge wiring, plug their generators into that, and get the "full" converter output going to their battery, but I'd prefer to get that same result with the already-installed, OEM converter. Thoughts?

[Wmlunt]

Your converter is rated in a specific wattage, likely 660 watts (55a x12v) output. The input is likely higher wattage input (transformers are not 100% efficient, in fact a lot is lost in heat) so maybe rated at 800-900 watt (input) converter.
A 800 watt device pulls about 6.95a at 115v. It will never pull 15 or 20 amps from your 115 volt power line extension cord.
The fact that you see lower amperage draw than the maximum rated current is likely due to the type of battery, lithium vs lead acid type(s) and charging stage, both of which maximize the battery life.
Likely a WFCO WF8995 which you can look up specs on their website.
Bill

[eatSleepWoof]

Thanks, Bill. That does clarify some of my confusion. Sounds like I assumed that the converter would draw more than it does.

My lithium batteries can definitely charge at much higher rate than what the converter is putting in, so I'm still not 100% clear that everything is working at max capacity. I'll look up the details of the converter.

[Morich]

A point to keep in mind on current flow on different equipment is some basics on charge for batteries.
Current flow can be somewhat like water flow for ease of understanding. We can see water!
One big point is that the flow is determined by the difference of two points as long as the resistance stays the same. Water 12 inches deep flows quicker to a level of 8 inches than it does a level of 10 inches. Flow (current?) slows as the levels come closer and closer to each other and stop when level.

In power that works the same. We get more current flow if we have a charger at 13 and a battery at 10 volts! As the charge voltage and the battery voltage come closer together current reduces!
Then there is often another factor whcih changes current flow when we don't want to overcharge or overheat the battery. The charger often has stages and backs the charge voltage and current flow down as the battery gets closer to ideal charge!

I rarely look at current flow as there are more things that can confuse current readings than simple voltage readings! Much of that choice is based on what we are used to doing and what equipment we have .

Basic idea is that current flow may change at different times and for different reasons.
Maybe the batteries are nearing the charge voltage, so less current flows? Maybe the charge voltage is lowered to avoid overheating?

Batteries are so simple but they are also very confusing!

[eatSleepWoof]

Richard - great analogy. I didn't know those details before.

The 9855 manual does state a max input of 940w / 11a.

So let me see if I understand this correctly...

The trailer's 30amp plug can theoretically allow 30amps to flow through; the converter will draw a max of 11amps, so up to 19amps could go to the power distribution panel's 120v appliances (bypassing the converter).

The manual does explain different states of the charging profile, and that the charging output will vary between them, as well as with other loads in play. That all makes sense.

OR am I wrong, and the max current for the WHOLE trailer is only 11amps? If so, then why bother with the 30amp connection, cables, etc? 11amps seems awfully low and wouldn't allow for simultaneous use of (for example) AC and Microwave, so this doesn't seem likely.

In any case, it seems like I'll need a separate, standalone charger if I want to get more current flowing from the generator to the batteries. Will think this over...

(I already do have a 40a DC/DC charger setup in place, but would love to get more charge from the generator, too.)

[powercat_ras]

The converter-charger (CC) is rated for 55 Amp MAXIMUM DC output, but it will normally be much less.

The converter-charger has 3 modes:

Bulk, this mode is used when the CC senses that the batteries it is connected to are at less than 80% state of charge (SOC). This is the only mode where the DC current will come anywhere close to 55 amp rating. In this mode the CC will output the maximum current it is capable of, the lower the state of charge of the batteries being charted, the higher the current will be. The CC voltage can be as high as 14.4 volts but generally will be less than that.

When the CC senses that SOC is 80-98 % it will drop out of bulk charge mode and enter topping charge mode. Charging voltage is reduced to around 13.6 volts and less current is delivered to the batteries being charged. This prevents the lead acid batteries from being charged at a level that would cause the formation of gas from the water-acid solution in the battery.

Finally, the CC will drop voltage again to a level that is just enough to compensate for self discharge, around 13.2 volts.

= = = = =

The AC power for the whole trailer can be up to 30 amps peak and about 27 amps continuous long term, without tripping the TT's 30 amp main breaker or the power pedestal 30 amp breaker.

The CC will generally will convert about 90% of the AC input power to DC output power so when in bulk mode a 55 A max CC will draw up to about 700 watts AC. ( 6 amps AC ).

Your TT has a 30 amp rated source "shore" power cable and this feeds to a circuit breaker box inside the TT very much like what is in a home, just smaller. It will have a 30 amp main, and several 15 and 20 amp branch circuit breakers. Generally the CC will be on a dedicated 15 amp breaker.

[Morich]

Another point on what the charger of whatever name we want to use will put outis a factor. What type of battery, lead acid or lithium is also a factor. Lead acid , in this case, charges slower.
It is a slow chemical reaction that has to go all the way down and through all the cells and all the chemicals before the battery can reach full charge.

In schools this can be really hard to get across to folks new to keeping batteries in good shape, so there are different ways to make it more understandable.
So maybe this makes it easier to see in our mind?

We can only test the voltage at the posts if we use the meter or monitors like the charger. We know that it takes time for that change in voltage (chemical reaction?) to reach all points in the battery.
We get what is often called surface charge as we charge and look at the voltage at the posts. The charge and voltage might be described as "building up" at the posts?
If we read the voltage too soon after taking the charge off, we still see near the charge voltage as the chemicals have not settled to become stable for the full battery voltage!

So to let it make more sense when we first look at it, we may hear it described as pouring something thick (Molasses?) in a hole in a small barrel. If we pour too quickly, it won't go in, so we can only pour it in as fast as the thick material will spread! Think of a cone of material right under the hole?

So it is a slow process and tends to let us see more voltage right at the post where we are looking, than is actual voltage of the whole battery ( or barrel!) so we get a false reading which is much higher than the real voltage of the whole.

Think how that effects the charging. If we start with a charge system that can put out 13-14 volts and a battery that is really down, say 8 volts. When we first power up the charger, the high voltage is 5-6 volts difference in potential, so we get a ton of current flowing.
The voltage DIFFERENCE is what changes the current if the resistance stays the same.

At first we get a ton of current because there is a large difference in voltage. But since the change is slow to move from the post to the rest of the battery chemicals, we might say the charge "builds up" at the posts. Like pouring Molasses in a hole in a barrel? You look in the hole and it looks full!

The charge equipment then senses the difference in voltage it is putting out compared to what it senses at the post and the difference is much less due to the "buildup" at the posts! That big 5-6 volt difference, soon becomes much less. A difference of 2 volts gets us much less current flow than the 5 or 6!
At some point after several hours of uninterrupted charge, things settle down and the charger settles on the output voltage that tends to charge the battery at a good steady rate but not so high it overheats or over charges the battery.
A newer charge system with better electronics and better regulation will be built to charge as fast as practical but not so fast it boils the water out or cooks the battery too much to let it last.

Current battery tech, will often gives us a charger with a bulk charge at first to get the battery as much as practical, then a lower voltage before finally moving down to a float charge level. That end is somewhat above 12.8 that the best lead acid can hold, but way below the bulk/quick charge voltage it starts with!

One of the ways we get things confused is the way we think of batteries. They CAN suppply the voltage we need to run things, but more often in the RV, we use them as storage for the excess power the charger is putting out above what the RV is using.
It is not a path that power goes in one side of the battery to get out the other but more like a side room storage area!


As long as the charge is higher than the use, excess goes to the battery. But if for some reason the use exceeds the charging, power comes out of the batteries. Like when we put it in when plugged but take it out when unplugged?
Whether we are putting power into the batteries or it is being taken out, depends on the DIFFERENCE between what the load needs and what the charger puts out.

Or kind of like our check book? We kind of like to store the excess money somewhere but we may find it coming out if the amount we make is less than what we spend!

[eatSleepWoof]

Great into, thanks both!

The voltage DIFFERENCE is what changes the current if the resistance stays the same.

I can see that's one of the most important details. Definitely great to understand.

[tinglett]

I was curious about this topic when I switched to Lithium and changed out my WFCO 8955 with a PD4655LIV. The best I would ever see was a brief peak at 40A or so, but generally it would quickly dribble down to 30A. I suspected voltage drop was the culprit (easy enough to estimate) and devised a little experiment. I brought a battery inside and connected it up directly to the charger with short 4 awg cables. I got about 53A...pretty much as expected.

Here is a pointer to the experiment: https://www.winnieowners.com/forums/...ml#post3878903

Eventually I installed an additional charger next to the battery and I use both chargers together when I want to charge up fast. I can get around 80A that way (which is ok for my 2 battery setup).

BTW, pretty much any generator has this capability. Even at 80A we are only talking 80A * 14.6v = 1168 watts. I posted about this setup here: https://www.winnieowners.com/forums/...er-364994.html

If I were to redo my entire setup, I'd probably pull the WFCO charger and leave the space empty, place a new 100A charger in storage bay right next to the batteries, and use the 6 awg factory cable to send power back to the distribution panel. Then the charger, solar controller, inverter, etc, would all be located together. But I doubt I'll ever do this. The journey to figure all this stuff out was actually half the fun .

[eatSleepWoof]

Thanks, Todd. Your earlier threads on the subject were a partial inspiration for this attempt.

My two 100ah batteries are already inside, under the bed. I've got 2awg wiring running from these batteries, under the tongue, to the original circuit-breaker setup on the tongue, where they connect to the same terminals that OEM batteries connected to. I didn't particularly want to re-wire original setup when initially building this.

I haven't opened up enough cabinetry to look at the converter just yet, but I'm wondering if it's worth running 2awg wiring from it directly to the batteries. Sounds like it might give me some gains.

[Morich]

Originally Posted by eatSleepWoof

Great into, thanks both!



I can see that's one of the most important details. Definitely great to understand.

It is one of the basic things in electronics as "Ohm's law" cover how any of the three functions changed effects the others.
It is so basic that you can get into discussions that last for ages and still not get full agreement!

I try to avoid those as it is like politics and just no point!

[tinglett]

Originally Posted by eatSleepWoof

I haven't opened up enough cabinetry to look at the converter just yet, but I'm wondering if it's worth running 2awg wiring from it directly to the batteries. Sounds like it might give me some gains.

I suspect you'll get a considerable gain from using 2awg. If you are fairly certain you want to run the cables, you might buy the cable and first run from the batteries around through the front door to your charger as an experiment. Obviously you can't really run it that way, but you can see how well it charges before you go to all the effort to pull apart the chloroplast and route the new wire under the trailer. I also don't see a reason why you can't use the new 2awg and original 6awg wires in parallel to gain a bit more.

Also, be very careful with those batteries (this is for others who are reading). Those batteries have a lot of energy in them and I'm sure you can do some accidental welding with them if you work with live wires, even at 13.3v! This is partly why I built a "battery box" so I could have them switched off with a breaker while working with wires.

[eatSleepWoof]

Originally Posted by tinglett

I suspect you'll get a considerable gain from using 2awg. If you are fairly certain you want to run the cables, you might buy the cable and first run from the batteries around through the front door to your charger as an experiment. Obviously you can't really run it that way, but you can see how well it charges before you go to all the effort to pull apart the chloroplast and route the new wire under the trailer. I also don't see a reason why you can't use the new 2awg and original 6awg wires in parallel to gain a bit more.

That's exactly my thinking on both counts. So long as the converter's terminals have enough room to double-up wiring + terminals, I'll run both in parallel.

I've got a bunch of 2awg leftover from various projects; probably not enough for the full, proper run, but might be enough to do the trial/test.

[tinglett]

Please keep us posted with your progress! I'm very curious at least . I'm also interested in how to mess with the chloroplast. So far I've stayed away from pulling it apart. I'm sure there are some good techniques and tricks with it.

[eatSleepWoof]

Originally Posted by tinglett

Please keep us posted with your progress! I'm very curious at least . I'm also interested in how to mess with the chloroplast. So far I've stayed away from pulling it apart. I'm sure there are some good techniques and tricks with it.

I pulled down the coroplast several times in various spots for various needs and have a bunch of photos scattered throughout the build thread on ExPo. Might be useful for you.

I don't anticipate having time to play with the converter/batteries in the short term, but will share an update when I do.

[bigb]

As mentioned the wire size will limit the current. As an experiment simply connect a spare length of heavy wire to your battery+ and touch the other end to your converter + output, you will see an immediate jump in charge voltage and current.

If you want to parallel some larger conductors into smaller lugs you can use a split bolt or a Polaris and splice the pairs together into one pigtail to fit the terminal lug, just be sure that the pigtail gauge is large enough for the total ampacity rating of the converter. A short pigtail like that will have practically no effect on voltage drop.

I've even considered leaving my conductors connected as they are inside the RV and tagging onto them underneath with split bolts to reduce the resistance but for now I added a lithium charger to the bay right next to the battery compartment and connected it to the batteries. Then I just plug it in, there is an outlet in that bay.

[Wmlunt]

I would not run multiple conductors in parallel to carry the load, especially different gauges. In home and industrial wiring the NEC does not allow multiple conductors in parallel to carry the load. As the wires heat up the resistance changes and more power shifts to the smaller gage conductor, which makes it heat up more, etc. I guess if the smallest conductor is rated to carry the amperage… it should not burn up. Wiring and electrical codes have been developed over decades of experience.
Bill

[bigb]

Originally Posted by Wmlunt

I would not run multiple conductors in parallel to carry the load, especially different gauges. In home and industrial wiring the NEC does not allow multiple conductors in parallel to carry the load. As the wires heat up the resistance changes and more power shifts to the smaller gage conductor, which makes it heat up more, etc. I guess if the smallest conductor is rated to carry the amperage… it should not burn up. Wiring and electrical codes have been developed over decades of experience.
Bill

Actually NEC does allow parallel conductors of 1/0 and larger of equal size and length, but that is not pertinent to this discussion of parallel 12 volt wiring which is commonly done on boats and solar. As long as the circuit is fused for the smallest conductor I don't see a problem or a prohibition. After all, the negative path in an automotive DC circuit is often in parallel with the frame.

Just to be sure though, I'm going to ask some of the electrical gurus on an electrical forum I belong to.

[BobC]

I remember wondering why my solar controller didn't show many amps flowing to my batteries even though my panels were in full sun. My simple way of understanding this is to think of batteries as smarter than me, they only eat based on how much they need.

[Morich]

As far as the heating on a parallel conductor, it may pay to think about current takes the path of least resistance.
If we have a large conductor and a small one, the small will have more resistance than the large, so more current goes to the larger!
Parallel paths are very common on circuit boards.