MPPT/DC to DC Charger for Trailer Build

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.

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?

"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?

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.

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 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.

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.

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?

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.

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.