MPPT charger problem: Is this going to work?

[dRdoS7]

Hi,

Hopefully this fits in the Forums Home < General < Renewable Energy and Storage (Non-EV) category.

Background:

I have a DC-DC charger with MPPT in our caravan. The DC-DC function works well.

Caravan Connected-no panels.jpg (28.91 KiB) Viewed 980 times

I recently installed a couple of solar panels.

Caravan Connected.jpg (32.42 KiB) Viewed 980 times

Problem is that it won't charge the Aux. batteries. Unless there is a 12V source at the input cable, solar charging won't work.

Caravan Disconnected-shrunk.jpg (34.02 KiB) Viewed 980 times

Here's how it's wired:

Wiring.jpg (104.91 KiB) Viewed 980 times

I have a spare AGM and connected it to the caravan Anderson plug, with an ammeter inline, and there was no current flow when it was connected. The AGM was at about 12V, and the caravan batteries were probably 13(ish)V. Solar charging worked.

Disconnected the battery.

I then connected a wire, with an inline spade fuse (30A resettable), from the DC-DC 12V output to the DC-DC 12V input, and that worked, but it (the fuse) got very hot after a short time, and tripped open. I had thought, if it worked, that I could use a switch or relay when disconnected from the wagon.

I tried a wire with a diode and a glass fuse between the main in and aux. out cables to see if that would work, it started the solar charging, but melted the solder on the cable/diode join eventually. I measured the current when I connected it, and IIRC there was only 0.1A. Reversed the cable and there was 15A. I don't know any specs of the diode it was one of several bits and pieces recovered from old (PC PS?) circuit board/s.

I then tried 3 diodes in parallel. Used a terminal strip at each end, so no melting solder. It didn't get hot though, and solar charging worked. There was a 0.03A current.

I read that I should put a resistor in series with each diode, so I'll do that if I can use it OK.

I was going to put a 24V NO relay controlled by solar input to switch my "fix" wire so it's only connected when there's solar. A 12V NO relay in the input cable to the DC-DC, so it only closes the "fix" wire circuit when the wagon is not connected, but I think that relay may stay closed with the 12v from the Aux batteries.

My questions:

• Is this safe to leave connected?
• Am I possibly going to damage to the DC-DC? I can't see how, but other eyes/brains might.
• Is there a better (& cheap ) solution?

I have 3 other options:

1. I can keep the DC-DC, and use 2 MPPT controllers I have, they are only suitable for one panel each, and that adds more wiring.
2. I can keep the DC-DC, and buy another MPPT that will support 2 panels. That adds more wiring too. That costs more $$.
3. I can return the DC-DC, and buy one that works when there's no 12V supply. I.E. caravan is disconnected. That costs more $$.

Before you ask: This is how the device is designed, it's not faulty. Really.

Thanks,

dRdoS7

[brendon_m]

When you connect the dcdc output to the input, it will be trying to charge the battery from itself. It will see (say) 14V on the input and try to charge the auxiliary battery flat out.
That's why it's getting hot, as far as the dcdc is concerned you have connected a main battery with infinite power available and there is a massive drain on the auxiliary battery, so it is working as hard as it can.
Probably not good for a long life.

By fitting a resistor inline it will drop the voltage on the input to the dcdc from 14V(or whatever it's set too) to something less but that will depend on load.
A better way would be to use a bunch of diodes in series with each one dropping 0.7V until you get to the desired voltage.
How the dcdc reacts from there depends on how it's set up.
If you find the sweet spot where it's powered up but below the "start charging from main" threshold it might work

But it all depends on the software.

Do you have a manual?

[T1 Terry]

What brand DC to DC is it? All the ones I use either switch internally dependent on which can supply the required current the best, others use a DPDT relay driven by the starter battery so the device becomes a DC to DC charger when the voltage sensing relay closes the circuit from the start battery to the Anderson plug at the rear of the tow vehicle where the caravan plugs in. Redarc is the only one that is an absolute PITA to work with, it requires the same voltage to be sensed on the ignition wire as the voltage on the DC to DC input, or it won't start up. This means the aux battery can not be used to drive the ignition sense so the aux batteries BMS can't turn the DC to DC on/off unless a relay is used to make/break the supply from the DC input side to the ignition sense .... an absolute PITA

T1 Terry

[Rusdy]

Option 4?

Return your DC/DC converter and buy another el' cheapo DC/DC converter. Then add another MPPT controller.

I've been buying mine from Hong Kong. Unfortunately with AUD tanked, it's getting more expensive.

I've been using this MPPT (click here) for myself in the last couple months, and works well so far.

Will require mucking around with cabling though...

[dRdoS7]

Hi,

When you connect the dcdc output to the input, it will be trying to charge the battery from itself. It will see (say) 14V on the input and try to charge the auxiliary battery flat out.

That was the reason I put in a diode after the first try. There's about a 1V drop over the diode.

That's why it's getting hot, as far as the dcdc is concerned you have connected a main battery with infinite power available and there is a massive drain on the auxiliary battery, so it is working as hard as it can.
Probably not good for a long life.

With only 1 diode it got hot, but with 3 in parallel it didn't. It seems to do what I want. Have a 0.03A going through the wire, and solar charging works. Just want to be sure what I've done is going to be OK. The reason I was going to put a resistor inline with each diode was that I read it will force the current to be shared between the 3 diodes. I don't know though, because I thought I was blocking the current, but I still got a voltage at the DC-DC input.

I've disconnected the "fix" for the moment, and put the temp battery back, until I can decide what to do.

What I'm not sure about is the relay I would like to put it to disconnect the "fix" when I connect to the car, that's to stop current bypassing the DC-DC.

Do you have a manual?

Not one that's of any use.

What brand DC to DC is it?

A cheap(ish) one! I think it's a Projecta knock off. Even some of the pictures they use are the same.

Option 4?

Return your DC/DC converter and buy another el' cheapo DC/DC converter. Then add another MPPT controller.

I've been using this MPPT (click here) for myself in the last couple months, and works well so far.

Will require mucking around with cabling though...

The DC-DC works well, so there's no point returning it, and buying another, unless it has MPPT that works.

I looked at those MPPT years ago, but thought (Youtube video) that they didn't work with 12V.

Thanks,

dRdoS7

[T1 Terry]

If the DC to DC works well, I'd look to getting an MPPT controller for the solar. While the DC to DC will also act as a solar controller, they aren't terribly efficient at it because that part is more of an added extra rather than a specially designed double duty unit. The other advantage is you can actually have both units charging the battery at the same time rather than one or the other working but not both at the same time. That's fine if you are only using the unit for DC to DC or portable panels and you have a second dedicated solar controller that looks after the solar permanently mounted on the roof.

T1 Terry

[dRdoS7]

Hi,

If the DC to DC works well, I'd look to getting an MPPT controller for the solar. While the DC to DC will also act as a solar controller, they aren't terribly efficient at it because that part is more of an added extra rather than a specially designed double duty unit. The other advantage is you can actually have both units charging the battery at the same time rather than one or the other working but not both at the same time. That's fine if you are only using the unit for DC to DC or portable panels and you have a second dedicated solar controller that looks after the solar permanently mounted on the roof.

T1 Terry

I've got 2 Victrons unused ATM. One was for a portable panel, and one was in the 'van, and handled both previous panels. Those were flexible, and failed after a couple of years. I bought the largest panels I could fit, and framed this time, but together (either series or parallel) they are outside Victron's specs. I could use both Victrons, as I won't be using the portable any more. Sort of as a weight trade-off. Plus it's a PITA.

I was trying to keep the number of devices & wiring in the battery box down, and found I needed a DC-DC since I swapped from AGM to Li. So, I bought the DC-DC, removed the old panels, and removed the Victron. Currently have 2 x 100Ah Li, 2 x AC chargers, the DC-DC, 2000W inverter, Battery monitor, fuses, etc., and a lot of cables.

While what I've done for the DC-DC seems to work as a fix, it's just going to be more complex with a couple of relays to switch it on/off as needed. Although I could just put in a manual switch. Not likely to forget am I? I wonder what will happen if I do, connect the wagon up, and drive for a few hours.

I think I'll return it, and buy a different brand. The seller is going to send a pre-paid label Monday, so I didn't have much time.

I'll make sure anything I buy can charge the Aux. batteries if the wagon isn't connected.

Still can't get over the fact they would make something like that, and show it installed in a caravan. I guess they don't own a caravan.

I haven't tested whether both functions will work together, as I'd probably get fined for going out on a test drive ATM. They do work separately.

After I found the problem, I did a search, and saw a review from a 3 months ago (I bought mine in Nov. 2019), he had the found that out too.

Thanks,

dRdoS7.

[rhills]

I think I'll return it, and buy a different brand. The seller is going to send a pre-paid label Monday, so I didn't have much time.

I'll make sure anything I buy can charge the Aux. batteries if the wagon isn't connected.

We've had the West Australian-made Intervolt DCC R2-0 in our motorhome for nearly two years now after we swapped our house batteries over to LiFePO4 chemistry and we swear by it. I've had some interaction with the manufacturer here (feeding back suggestions) and I have found them very responsive and customer-focused. I don't work for them or have any vested interest in the company apart from wanting to see an Aussie manufacturer succeed.

They probably aren't the cheapest unit you will find, but it does what it does very well.

Cheers,

[dRdoS7]

Hi,

We've had the West Australian-made Intervolt DCC R2-0 in our motorhome for nearly two years now after we swapped our house batteries over to LiFePO4 chemistry and we swear by it.

They probably aren't the cheapest unit you will find, but it does what it does very well.

Cheers,

I did look at them, but they are 25A, so there's not much left (10A?) for the Aux. batteries after powering the 3-way.

Also, they are only 250W solar. I didn't think the price was too bad though.

Was looking at a Renogy 50A with MPPT. It is only 25A from either car or solar, so not perfect. I asked on caravan forum, and the poster said his works, but I've messaged Renogy just to make sure. Can't be too careful!

Next best option seems to be a Projecta IDC 45A.

Or, I may give in, just buy a bigger Victron MPPT. Keep the current DC-DC.

Thanks,

dRdoS7

[brendon_m]

Redarc is over priced and underwhelming. The few intervolt's I've fitted seem to be pretty good but I don't see lot of them, not sure why.

Sadly we normally fit redarc simply because it's the easiest to get from our suppliers and it's a brand most people have heard of so they feel safe buying a known brand. You can have the best product at the cheapest price but marketing always wins

My work is an agent for both redarc and intervolt but when giving advice we normally recommend Enerdrive units as they seem to be better value for money and actually undersell the specs rather than promise more then they can actually deliver.

https://enerdrive.com.au/product/epower ... -40a-plus/

[reecho]

Hi,

We've had the West Australian-made Intervolt DCC R2-0 in our motorhome for nearly two years now after we swapped our house batteries over to LiFePO4 chemistry and we swear by it.

They probably aren't the cheapest unit you will find, but it does what it does very well.

Cheers,

I did look at them, but they are 25A, so there's not much left (10A?) for the Aux. batteries after powering the 3-way.

Also, they are only 250W solar. I didn't think the price was too bad though.

Was looking at a Renogy 50A with MPPT. It is only 25A from either car or solar, so not perfect. I asked on caravan forum, and the poster said his works, but I've messaged Renogy just to make sure. Can't be too careful!

Next best option seems to be a Projecta IDC 45A.

Or, I may give in, just buy a bigger Victron MPPT. Keep the current DC-DC.

Thanks,

dRdoS7

I have used the Renogy 50A DC/DC converter for a while. Works well. Doesn't need the main battery connected for it to work. PV input float charges the main battery once the aux battery is full. Genuine 50A charging too.

[dRdoS7]

Hi,

I have used the Renogy 50A DC/DC converter for a while. Works well. Doesn't need the main battery connected for it to work. PV input float charges the main battery once the aux battery is full. Genuine 50A charging too.

Good to know.

These are the messages to, and back from Renogy:

ME:

Will it charge the House battery with solar if the Start battery is not connected, such as in a caravan, when it is not hitched to the tow vehicle?

REPLY:

If the alternator is smart alternator, the ignition line must be connected between the D+ terminal of the alternator and the D+ terminal of the battery charger, the line will give the battery charger a start signal when the alternator starts working.

If you do not need charge house battery through alternator, you can just buy a solar controller,

ME:

I want to charge the caravan (house) battery with the DC-DC charger from the tow vehicle alternator/battery (starter), & the solar panels mounted on the caravan. Because the vehicle is only attached to the caravan when towing, I need to know if the MPPT function of the DC-DC charger will charge the caravan batteries from solar if the vehicle's starter battery cable is not connected to the caravan.

I have attached a diagram.

NO REPLY.

ME:

I sent a reply already to ask again if this will work OK in a caravan with solar panels, and charge the Aux. battery if the stater battery is not connected, but have not had a reply from you.

REPLY:

Very sorry for the late reply, we are testing a new customer service system which caused some missing messages.

If the stater battery is not connected, this charger cannot charge the aux battery through the alternator.

ME:

No worries, but I would like to know if it will charge the aux. battery from solar if the starter battery is not connected.

We have a caravan, which naturally is not always connected to the tow vehicle. I will install the DC-DC in the caravan. I need to be sure it will still charge from the caravan's solar panels even if the starter battery is not available.

REPLY:

The solar panel can charge even if the ignition line does not connect to alternator.

I think I'll just buy one.

dRdoS7

[dRdoS7]

Hi,

I think I'll just buy one.

dRdoS7

So, 1 left in stock this morning, which I bought.

Then I get an email that they're out of stock!

dRdoS7

[brendon_m]

Problem there being that you are discussing with someone who probably knows little about the actual product and have just been told to read the manual to answer questions

[dRdoS7]

Hi,

Problem there being that you are discussing with someone who probably knows little about the actual product and have just been told to read the manual to answer questions

Yeah!

I think that would be less than a little, or 4/5 of 3/8 of SFA.

Luckily I already knew the answer, from 2 users. I would have liked to have it in writing, especially after the last controller.

Now, just have to get my hands on one.

Still, no rush. We're not planning on leaving until mid-June, so hopefully we'll be able go, and be ready.

Booked a few caravan parks for the first 4 weeks, won't need much solar there, then wing it.

Thanks,

dRdoS7.

[rhills]

In case it helps, I've just been advised by my contact at Intervolt that the Solar input in the R2-0 is no longer limited to 250W. The solar input is now up to to the 25A limit for Alternator charging. I can confirm from our own usage that this unit will charge from solar with the ignition switched off.

Watch out also for temperature de-rating. I am aware that the guys at Intervolt put a lot of effort into minimising any temperature de-rating in their units, knowing that they will operate in pretty ferocious environments in outback Aust.

Yes, I know I'm a bit of an Intervolt fanboy, but I like to support Australian companies when they make good quality gear.

Cheers,

[brendon_m]

Yes, I know I'm a bit of an Intervolt fanboy, but I like to support Australian companies when they make good quality gear.

To be fair, credit where credit is due. The intervolt units are really good quality and tick all the boxes for most people, not to mention they have a lot of features that make them quite versatile (like the remote display/controller).

Their biggest flaw is the lack of market penetration, but that can only be fixed with advertising and time.

[dRdoS7]

Hi,

In case it helps, I've just been advised by my contact at Intervolt that the Solar input in the R2-0 is no longer limited to 250W. The solar input is now up to to the 25A limit for Alternator charging. I can confirm from our own usage that this unit will charge from solar with the ignition switched off.

Even with 300W, it's still going to limit the solar output. Also, as I wrote previously, my caravan's 3-way will take most of the 25A (190W element). I prefer to have more charging than I need. Worst case, I can run the 147kW genny.

Watch out also for temperature de-rating. I am aware that the guys at Intervolt put a lot of effort into minimising any temperature de-rating in their units, knowing that they will operate in pretty ferocious environments in outback Aust.

Never, ever going outback. Maybe Lake Eyre again, one day, when it's really full, and water's flowing down the Goyder Channel. Heat is the enemy of the wife. Not keen on it myself. Unless near the sea.

Yes, I know I'm a bit of an Intervolt fanboy, but I like to support Australian companies when they make good quality gear.

Seeing that Renogy ran out of stock, conveniently just after I'd paid for the "last one", I decided to buy a Redarc 40A. Express posted for $550. More than I was going to pay, and I'd said (to myself) I'd never buy Redarc, though I do have one of their brake controllers.

dRdoS7