DC-DC Charger - Choosing the right amperage?

[dhod]

Starting the terrifying exciting journey into electrics and one thing i'm struggling to find a clear guide on is what amperage I need and if there's a downside to getting more.

Useful Context:
Transporter T6 late 2015 (still need to work out if it's a smart alternator)
AGM Leisure Battery of around 220ah (either 2 in parallel or one big - that's a whole other question)
350W-400W Rigid Solar Panels being fitted (need to measure up size)
Main items that will draw power are 12v dometic fridge, 12v sockets, 12v strip lights and normal lights
Will have 240v plugs that will only be accessible when connected to electric hook up

DC-DC Choices
Whittled it down to either the standard Victron Orion which is 30A or the Renogy which can go 40/50A - i'll most like get a separate MPPT in either case so a dual one isn't necessary.

So my main question is how do i work out what I need? I read somewhere about ensuring you don't overload the alternator so perhaps i don't want to get one too big. But not sure where the right place to focus on working things out is? Any help is v much appreciated. Trying to get everything purchased in the next week or so for the big electric fit out over the easter bank holiday

 

[Dellmassive]

Have a look over here:

Dellmassive’s "How I Done It" blogs.

-- Dellmassive`s -- "How I Done It" -- thread -- ************************************************** Dellmassive`s -- "how I Done It" -- Thread ************************************************** Kit List And Stuff -- How I Done It & What I Use --...

www.t6forum.com

.

 

[Lanky]

I am just starting down the same road as you Dhod.

I will be very interested to hear the replies you get.

 

[dhod]

Have a look over here:

Dellmassive’s "How I Done It" blogs.

-- Dellmassive`s -- "How I Done It" -- thread -- ************************************************** Dellmassive`s -- "how I Done It" -- Thread ************************************************** Kit List And Stuff -- How I Done It & What I Use --...

www.t6forum.com

.

Thanks for this. So from this section of your 'how i done it':

What size DC-DC charger do i need?
.... Add the Battery charge rate of 10-20A plus the Loads draw rate of 10A give you a figure of 20-30A.

If i find i'm at say ~26-27A using basic maths would it be "safer" to go for something like a 40A or is there a concern with having a lot more than you need?

 

[EAN]

Personally I’d start with thinking where you are going to locate everything. 220ah of AGM battery/batteries is going to take up quite a bit of space and you only get 1/2 of the capacity quoted as useable. Have you considered using a LiFePo battery? More useable capacity in a smaller size. Of course requires chargers with a lithium profile.

You need to consider the cable runs also. More current requires bigger cables and also longer distances requires bigger cables due to the voltage drop.

How are you going to use the van?
I did some of my own calculations on a Dometic fridge and I reckon running it for 24hrs would take about 40-50ah.
You have quite a decent amount of Solar specified and in the Summer months I would expect it would keep you well topped up without driving anywhere.

Are you going to have a mains charger for the leisure battery, when you are on hookup?
Do you want to trickle charge the starter battery?

I think I’ve read on here that the Orion can run hot.
The Renogy is available in 50A and 30A; the case size is the same but I believe you can reduce the current via its app, so of the two I’d go with the 50A regardless.
I’ve ignored the Solar MPPT input on the Renogy, as in your case with the amount of Solar you are installing is likely to exceed the Voltage spec of the Renogy input anyway, so you are better getting a dedicated MPPT controller to suit your panels.

 

[t0mb0]

Choose a battery first, that will specify the maximum charge current it will accept and therefore dictate what DC-DC you need, you can double that rated charge current if running two batteries in parallel.

As a previous poster says, the Victron Orion can run very hot, I'd only consider this if you have decent airflow.

 

[dhod]

Thanks for the advice so far.

The current plan is to have the DC/DC under the drivers seat (captains seat) and then the battery somewhere close by. I'm having my kitchen run the width of the van directly behind the seats so potentially somewhere around there. I keep going back and forth on lifepo's as the price seems so prohibitive (victron 100ah = ~£800, renogy 100ah = ~£450) vs £300 for a 220ah AGM

Are you going to have a mains charger for the leisure battery, when you are on hookup?

That's the plan yes

Do you want to trickle charge the starter battery?

No idea on this - haven't got this far into the "full plan" as of yet

 

[t0mb0]

Thanks for the advice so far.

The current plan is to have the DC/DC under the drivers seat (captains seat) and then the battery somewhere close by. I'm having my kitchen run the width of the van directly behind the seats so potentially somewhere around there. I keep going back and forth on lifepo's as the price seems so prohibitive (victron 100ah = ~£800, renogy 100ah = ~£450) vs £300 for a 220ah AGM


That's the plan yes


No idea on this - haven't got this far into the "full plan" as of yet

First place to start is to get a real idea of the intended use case. What appliances/loads are you going to have, how much are you going to be off-hookup, etc.

 

[dhod]

First place to start is to get a real idea of the intended use case. What appliances/loads are you going to have, how much are you going to be off-hookup, etc.

Intended use case is ability to be off grid max 3 days.
Most of the time we'd be moving around Europe mainly through campsites but having the ability to pull up for a few nights somewhere off grid if adventure takes us that way. As there's going to be no fixed toilet/shower/waste water going in the van there's no plan to be able to do that for more than 2 nights before returning to a campsite.

Appliances:
Dometic CX50
2x 12v Sockets
3x LED Spotlights
2x 1000mm 12v Lightstrips
1x 12v Waterpump

Hot water will come from solar and/or stove.
Heating will come from eberspacher (so may need a little bit of battery to power the controller)
Cooking will come from stove

Hookup
As mentioned we plan on having a 240v hookup when at campsite but no plans to be able to switch between 12v/240v when off grid. So hookup > charge battery > power 2x plug sockets would be intended use case there

So yeah really we're designing the van that will mainly be used at campsites but ensuring it's usable and friendly when off grid

 

[t0mb0]

Intended use case is ability to be off grid max 3 days.
Most of the time we'd be moving around Europe mainly through campsites but having the ability to pull up for a few nights somewhere off grid if adventure takes us that way. As there's going to be no fixed toilet/shower/waste water going in the van there's no plan to be able to do that for more than 2 nights before returning to a campsite.

Appliances:
Dometic CX50
2x 12v Sockets
3x LED Spotlights
2x 1000mm 12v Lightstrips
1x 12v Waterpump

Hot water will come from solar and/or stove.
Heating will come from eberspacher (so may need a little bit of battery to power the controller)
Cooking will come from stove

Hookup
As mentioned we plan on having a 240v hookup when at campsite but no plans to be able to switch between 12v/240v when off grid. So hookup > charge battery > power 2x plug sockets would be intended use case there

So yeah really we're designing the van that will mainly be used at campsites but ensuring it's usable and friendly when off grid

Ok, the good news is that that's a very reasonable and very typical kind of requirement, you're likely not going to need anything crazy. In fact, it's extremely close to my own scenario. For what it's worth, I still have the 75Ah factory fit leisure AGM along with a 20A DC-DC (might be 30A?) and a 250W solar panel. With this setup, on summer road trips around UK/Europe we can effectively stay off-grid from an electrical perspective for an unlimited time. As you correctly allude to in your post, the limitations on staying off-grid in this scenario aren't electrical at all, but water/toilets/showers. With this in mind, I'm not sure you really need 220Ah of AGM, which would be very bulky and heavy. Given your requirements, I'd be tempted to stick in a single 110Ah(ish) AGM battery, and you can always switch to lithium down the road if you feel the need (make sure your MPPT and DC-DC are compatible so these are future-proofed).

The only real scenario this wouldn't work out for you is if you're static in one place for 2-3 days without sunshine for solar, and can't or don't want to run the engine - if you think this will be common then maybe consider more battery storage. However, for road trips in places/seasons with a bit of sunshine, I think you'll be fine.

 

[True Romance]

Ok, the good news is that that's a very reasonable and very typical kind of requirement, you're likely not going to need anything crazy. In fact, it's extremely close to my own scenario. For what it's worth, I still have the 75Ah factory fit leisure AGM along with a 20A DC-DC (might be 30A?) and a 250W solar panel. With this setup, on summer road trips around UK/Europe we can effectively stay off-grid from an electrical perspective for an unlimited time. As you correctly allude to in your post, the limitations on staying off-grid in this scenario aren't electrical at all, but water/toilets/showers. With this in mind, I'm not sure you really need 220Ah of AGM, which would be very bulky and heavy. Given your requirements, I'd be tempted to stick in a single 110Ah(ish) AGM battery, and you can always switch to lithium down the road if you feel the need (make sure your MPPT and DC-DC are compatible so these are future-proofed).

The only real scenario this wouldn't work out for you is if you're static in one place for 2-3 days without sunshine for solar, and can't or don't want to run the engine - if you think this will be common then maybe consider more battery storage. However, for road trips in places/seasons with a bit of sunshine, I think you'll be fine.

Same here factory leisure battery fitted and never been an issue.

 

[Stay Frosty]

100Ah LiFepo4 battery would near enough be the equivalent of 220Ah AGM, the Renogy DC 50 mppt solar voltage limit could probably be solved by checking the panel output voltage level and choosing accordingly plus running panels in parallel but realistically if only three days off grid is a fixed limit then as per the two previous guys, on our camper with no solar it's the Waeco CRX50 that eats the lead acid in a couple of days during summer.