MPPT/DC to DC Charger for Trailer Build

[halhawkins]

Hello all, first time poster.

I am currently doing a special purpose conversion of my enclosed gooseneck and am at the point to figure out electricity. I have a lot of 12V equipment, especially strip lighting that takes up more amps than shore power (coming from the generator) can provide. The 120v equipment/AC will use about 24a. The 12v equipment will use about 90a and each job for the trailer will be about 2 hours so a total of 180a will be used, so my idea was to use two deep cycle batteries as the main source of power with the batteries being charged while driving/hooked up to truck or when connected to shore power.

I thought a DC to DC charger like the Renogy DCC50S 12V 50A DC On-Board Input MPPT Charger would work but Renogy told me that using shore power with an AC to DC converter would not work with the device in lieu of solar power. So I am trying to find a device that would charge the batteries from 2 different sources. Its very unlikely that the 2 power sources would be used simultaneously to charge batteries (but possible?). I've put a rough draft schematic below to give you all an idea. Would love to hear your thoughts. Thanks very much in advance.

[pianotuna]

58 meters x 11 watts = 638 watts.

638 / 12 volts = 53 amps

Better to use 120 volts.

[CA_Traveler]

halhawkins wrote:
Yes LED. From what I've calculated the strips at 60 led/m uses about 11W/m so that would be about 54a at 58m in length.

54A is huge and will require multiple wires to the lights. Likely more practical to use 4x 50' strings with 120VAC. Are you sure the LEDs use 12V vs some other voltage?

Don't know what equipment you're running etc but heavy draw 12V equipment draws 10x the amps than 120V and needs larger wire.

[Grit_dog]

halhawkins wrote:


Thanks. FYI the rooftop A/C (15k Recpro unit) I have is specced for a 15a breaker.

Would adding 2 more batteries suffice then? I already have the 30A generator, so I'd rather not have to switch to a 50A generator. That's a big part of the issue.

Yes, that was one of my points. By adding battery capacity and/or also changing types of batteries. (Normal 12V deep cycle or hybrid batteries are the least effective and efficient for a dedicated deep cycle scenario.)
But you also really don't want to max out the discharge rates of the batteries, at least not very often (scenario where you're running off batteries with no gen/converter charging).

Quick numbers, 400ah of capacity would give you a little headroom and not work the batteries like rented mules.

None of us know exactly what you're trying to accomplish, but if you will "always" have the generator running (assuming whatever you do can't "do" without the AC power stuff (and you don't have plans for an inverter)) then it would be more betterer to run everything or almost everything off of AC power, with no converting or inverting, from an efficiency standpoint.

[Grit_dog]

CA Traveler wrote:
DC to DC chargers are used for limited battery charging and boosting the voltage.

Do most DC DC chargers have a low duty cycle? What are the limits of them?
I thought they are able to work basically continuously as needed

[halhawkins]

Grit dog wrote:

halhawkins wrote:


No the generator is what is going into the shore power.

Why couldn't two batteries with 115ah each handle 90a load?

Gotcha, genny = shore power.
Batteries 2 115ah 12V FLA, SLA or AGM batteries have theoretically 230ah total at brand new 100% charged.
So at 90ah of draw, no charging, they are in need of being recharged in less than an hour (keeping with the 70-80% min charge for max service life) or in just over an hour they are dead as doornails at 50% SOC.

Rough numbers, you need to be feeding the 2 batteries, idk, around 50-60amps of charging just to barely hold your own in a perfect world scenario. Happens to also be that around a 25A rate is about the max you can charge a typical 12V deep cycle like you're proposing.

So if you had a 60A converter charging full tilt the whole time, theoretically you have "just enough" charging and capacity to maintain that load and not kill or shorten the battery life significantly.

Say you're pulling about 10A AC from the genny to run the converter, you're still looking for another 25A AC (per your calcs) for the A/C and AC outlets. 15A is LOW for the A/C when it cycles.
So all in, you have marginal battery reserve power ("marginal" being generous), full max charging out of a BIG converter that basically will try to charge the batteries too fast (it actually won't, it'll be putting all its power straight to the load basically) and it will all require a 4kw + generator, basically putting you out of the "quiet" generator market without spending big bucks there.

So yes with a big generator and a big converter, you can make the milquetoast battery capacity work, but everything will be running full throttle at basically 100% load and duty cycle.

All this without also considering inefficiency losses due to converting and inverting power.

Simple solution is to provide more DC power storage capability since you're already spending a bunch of money and give the batteries and the rest of the hardware a break.

This assuming your power draw calcs are right and not low, which makes the situation worse, or considerably high which lessens the issue.

There's a reason there's a sort of "practical limit" on what your proposing which is pulling more juice than most all RVs and many homes and why "houses" don't use DC power and why solar power arrangements have huge battery banks when they're providing significant power.

Youd be better off figuring out how to NOT pull most of your power DC and get it most/all to AC and find a nice big generator setup like a diesel Onan to run the whole show and keep the batteries for what they were intended for.

Thanks. FYI the rooftop A/C (15k Recpro unit) I have is specced for a 15a breaker.

Would adding 2 more batteries suffice then? I already have the 30A generator, so I'd rather not have to switch to a 50A generator. That's a big part of the issue.

[CA_Traveler]

OK a long string of lights. Yes 6V series/parallel. A true 12V deep cycle battery is rather expensive. A 12V Marine deep cycle battery is a tad better than a starting battery.

[halhawkins]

CA Traveler wrote:
Connect the AC/DC converter which should be a 3 stage charger directly to the batteries. Unlikey the alternator of wiring can supply 30A. DC to DC chargers are used for limited battery charging and boosting the voltage.

30A + for lights? Are you using LEDs?

Normal flooded battery discharge is 50% which is 115AH for both. Flooded battery voltage tapers down with discharge. For your application consider 4x GC2s like Trojan at 220AH each for 440AH or 220AH total, or maybe 6x. Lithium batteries are likely much better for your application since they have no voltage sag until about 20% charge left.

Perhaps you should consider a larger gen or 2 in parallel. 2 2000W gens would provide 4000W and perhaps run the A/C at the same time.

Yes LED. From what I've calculated the strips at 60 led/m uses about 11W/m so that would be about 54a at 58m in length.

I can't find Trojan GC2 in 12v. Are you referring to the 6V in a series/parallel connection?

[CA_Traveler]

Connect the AC/DC converter which should be a 3 stage charger directly to the batteries. Unlikey the alternator of wiring can supply 30A. DC to DC chargers are used for limited battery charging and boosting the voltage.

30A + for lights? Are you using LEDs?

Normal flooded battery discharge is 50% which is 115AH for both. Flooded battery voltage tapers down with discharge. For your application consider 4x GC2s like Trojan at 220AH each for 440AH or 220AH total, or maybe 6x. Lithium batteries are likely much better for your application since they have no voltage sag until about 20% charge left.

Perhaps you should consider a larger gen or 2 in parallel. 2 2000W gens would provide 4000W and perhaps run the A/C at the same time.

[halhawkins]

pianotuna wrote:
Hi,

Two possible routes.

1. get a hybrid inverter charger. These allow for load support. That means power may be drawn from the battery bank to make up temporary shortfalls in power.

2. There are some inverter chargers that have 2 AC input sources.

A side question. Why do your dc strip lights draw so much power, and what are they being used to light up?

On my last trip I often only had 15 amp shore power with no access to the breaker panel. I set my hybrid inverter/charger to not draw more than 13 amps. When using the microwave I do see over 200 amps being drawn from the batteries.

Be aware that "load support" is not "voltage support". To have voltage support one needs an autoformer.

There's about 60m of RGB strip lighting (special design for aesthetic purposes) and from what I've calculated that is about 54a (60 led/m 5050 at 11W/m or 638w total). There's also exterior and underbody lighting which is about another 8a. Other items using 12V but not continuously are the awning (6a) and the powered vent (5a).

The generator is the shore power so getting 30a from that continuously shouldn't be an issue.

[Grit_dog]

halhawkins wrote:


No the generator is what is going into the shore power.

Why couldn't two batteries with 115ah each handle 90a load?

Gotcha, genny = shore power.
Batteries 2 115ah 12V FLA, SLA or AGM batteries have theoretically 230ah total at brand new 100% charged.
So at 90ah of draw, no charging, they are in need of being recharged in less than an hour (keeping with the 70-80% min charge for max service life) or in just over an hour they are dead as doornails at 50% SOC.

Rough numbers, you need to be feeding the 2 batteries, idk, around 50-60amps of charging just to barely hold your own in a perfect world scenario. Happens to also be that around a 25A rate is about the max you can charge a typical 12V deep cycle like you're proposing.

So if you had a 60A converter charging full tilt the whole time, theoretically you have "just enough" charging and capacity to maintain that load and not kill or shorten the battery life significantly.

Say you're pulling about 10A AC from the genny to run the converter, you're still looking for another 25A AC (per your calcs) for the A/C and AC outlets. 15A is LOW for the A/C when it cycles.
So all in, you have marginal battery reserve power ("marginal" being generous), full max charging out of a BIG converter that basically will try to charge the batteries too fast (it actually won't, it'll be putting all its power straight to the load basically) and it will all require a 4kw + generator, basically putting you out of the "quiet" generator market without spending big bucks there.

So yes with a big generator and a big converter, you can make the milquetoast battery capacity work, but everything will be running full throttle at basically 100% load and duty cycle.

All this without also considering inefficiency losses due to converting and inverting power.

Simple solution is to provide more DC power storage capability since you're already spending a bunch of money and give the batteries and the rest of the hardware a break.

This assuming your power draw calcs are right and not low, which makes the situation worse, or considerably high which lessens the issue.

There's a reason there's a sort of "practical limit" on what your proposing which is pulling more juice than most all RVs and many homes and why "houses" don't use DC power and why solar power arrangements have huge battery banks when they're providing significant power.

Youd be better off figuring out how to NOT pull most of your power DC and get it most/all to AC and find a nice big generator setup like a diesel Onan to run the whole show and keep the batteries for what they were intended for.

[pianotuna]

Hi,

Two possible routes.

1. get a hybrid inverter charger. These allow for load support. That means power may be drawn from the battery bank to make up temporary shortfalls in power.

2. There are some inverter chargers that have 2 AC input sources.

A side question. Why do your dc strip lights draw so much power, and what are they being used to light up?

On my last trip I often only had 15 amp shore power with no access to the breaker panel. I set my hybrid inverter/charger to not draw more than 13 amps. When using the microwave I do see over 200 amps being drawn from the batteries.

Be aware that "load support" is not "voltage support". To have voltage support one needs an autoformer.

[Lwiddis]

"I have a lot of 12V equipment, especially strip lighting that takes up more amps than shore power or the generator can provide."

You are using more than 90 amps for lighting? What are you lighting?

[halhawkins]

Grit dog wrote:
So you’re planning on running shore power and generator at the same time to get your 24A AC power?
On the DC side I’d think the converter would go straight to the batteries, not thru the DCDC charger.
And you’re not going to pull enough power off your trucks 12V pin on the trailer plug to power a 50A DCDC or even a 30A DCDC.
And you’re going to have to pull a full load on the converter to keep just 2 batteries alive for 2 hours pulling 90ah. Better get a big one. Or more/better batteries.

No the generator is what is going into the shore power.

Why couldn't two batteries with 115ah each handle 90a load?

[Grit_dog]

So you’re planning on running shore power and generator at the same time to get your 24A AC power?
On the DC side I’d think the converter would go straight to the batteries, not thru the DCDC charger.
And you’re not going to pull enough power off your trucks 12V pin on the trailer plug to power a 50A DCDC or even a 30A DCDC.
And you’re going to have to pull a full load on the converter to keep just 2 batteries alive for 2 hours pulling 90ah. Better get a big one. Or more/better batteries.