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lief ryan avatar image

Can I use the MPPT to Dump Load?

do the victron mppt charge controllers have a dump load option?

MPPT - Solar Charge Controller
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Markus avatar image

No, they do not. Unfortunately. Maybe, if we pray to the lord, @mvader (Victron Energy Staff) there will be a supported solution in future. ;o)

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thanks, the brain racking continues :)

valos avatar image

I'm using the Multiplus on a 48V system to divert the excess power to a 1,2 KW boiler.

Multiplus has a relay that controls a contactor which turns the boiler on/off.

Multiplus turns on the contactor/boiler when VDC > 54V.

It turns off the contactor/boiler when VDC < 52V or AC load > 2000 W.

I noticed that if the PV output drops for whatever reason (a passing cloud) the boiler doesn't draw current from the battery for more than 10 seconds before it gets disconnected so it doesn't have a significant impact on the battery.

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that was my original plan, but i was worried about that putting too many (micro) cycles on the battery, it would be interesting to hear from the battery manufacturer about how it handle this kind of treatment?, what batteries are you using?

i've just received my pylontech batteries today, multiplus and charge controller should be arriving tomorrow, but i still have to build a shed and mount the panels before i can start playing with the setup.

i read an article about lithium batteries liking a 75%-25% charge/discharge cycle, a big drop in usable capacity but huge increase in battery life.

Good Day Vaos,

Your setup seems quite similar to mine and already did what I am planning to achieve. Could you please share more info about how is your setup? Do you have 220v 1,2kw boiler or 48v?I am planning to use 48V 1500W Water Heater (banggood sku:1344321) or an array of headers as an addition to the gas header and its 300L boiler. I still have time (until spring) to start this modification and to play with multi48/5000 settings but I will be glad if you can share where you defined VDC and other conditions for relay. Do you have any thermal sensor on the boiler to prevent overheating?Thx

Hi, sorry for the late reply, I'm using a water heating resistor with thermostat.

The thermostat is set at 60 degrees celsius.

I'll try to post a screenshot with Multiplus settings for this.

hi, what voltage source are you using to drive the relay for the 1.2Kw heater?

i have just set my dump load up today using the programable relay on the multiplus, but found that the relay was cycling really fast (like a PWM controller) to match the load (1Kw heating element) to the available excess solar power, that would be good but i don't think the multiplus relay would last long, did you have the same problem? i'm now using the relay on the smartsolar mppt, it has an option to use float status = relay on absorption = relay off, that works but not as efficiently

hummingbear avatar image

Would be huge if Victron could provide this. I have older flooded LA batteries and don't want to cause a bunch of micro cycles on them by hacking it into a relay

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Michael Riley avatar image

For the 'boat' community we definitely want to utilise as much solar as possible and heating water is a regular requirement. As a sailboat we do not always have our engine (water heating) on so solar or generator are the only other options (aside from taking a swim). We are today installing 2(3) x 200Ah LiFePo4, 24/5000 VA Multi, VenusGX, MPPT, 2 x BP220 + VE.Net BMS protection etc. We have a 4.5kW generator & 1kW solar (nom) + 16A (230V) shore power obviously (infrequently). We are (intending) connecting the AC water heater circuit (relay activated by VenusGX) and AC supplied by Multi as a dump load based on SOC + MPPT in charge (i.e. we have sun). Located generally in the South Pacific (east coast AUS currently) solar is most often available. Not sure how this will turn out over time and any suggestions / warnings welcome.

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Caren avatar image

Can the relay mode be used for the dump load settings?

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This could work, but it is unfortunately not officially supported, and you are on your own.

Moz avatar image
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@Moz Why not to switch the (or some) PV Panels directly to a heater (separate heating element) with BMV + relay?

Because we get more power by using an MPPT controller than by hooking PV directly to a resistor. And since we have the controller...
In practice it's a question of whether you prefer to have extra wear and tear on the batteries from lots of little 100%->95% discharge cycles, or less power into the hot water from a direct connection.
Hence the ongoing requests for Victron to support MPPT into a resistive load :) I'm sure at least one person a year would use that feature.

We are talking about excess power? ;o)

Do you expect a 30% better heating time? (MMPT comparison to PWM)

I would prefer this, rather than to thrill my batteries and high tech electronics to sweat into some resistor heating device... :o)

In my case I want the hot water so 30% extra makes a real difference in the winter. It's less about the cheap second hand solar panels I can get and more about where I put them on my truck.

Since the MPPT controller should last 5+ years of continuous use I don't really see that as the limiting factor, it's the batteries that are the problem.


I have been looking at making a bigger DIY MPPT to feed the resistive load but when I'm dealing with a 2kW array I get a bit scared. The 100W one I have works, but there's a whole lot of electronic design issues that become much more important when you have a couple of kilowatts (at 200V!)

It also kind of offends my sense of efficiency/waste that I will have all the hardware I need, what I need is software. It's very "I should be able to just hook this up" - resistive loads are the easy ones to drive

:o) Nice! I like the DIY way. Keep on!

When batteries go down to 95%, the heater stops? Connected directly, it would heat more time maybe...

With the batteries it will heat 100% of the time (once the batteries are over 95% and assuming there's enough solar input). With direct connect it will also heat 100% but at lower power. Once I get the setup built I will start comparing the two and it will probably end up that I only need to use the batteries a couple of months of the year.

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In NSW 2400W of panels should average 4.8kWh/day in winter unless it's actually raining. With a 30 litre tank that's ~1.5kWh to got from 20 degrees to 60 degrees. My hope is that even when it rains I'll have enough hot water to shower after riding my bike home.

The big cheat is to drain the tank when it's hot, then refill it later. Otherwise you're diluting the hot water. But that is a very manual process and probably only practical for one person or a couple.

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FWIW this really only works with lithium batteries where the number of cycles from actual rated capacity 90%-95% is very large. With lead batteries that would kill them quickly (the gap between "more than 10,000 cycles" and "1000 if you're lucky" bites really hard).

Why not using some capacitors then, to preserve the batteries ?

Ian Hamilton avatar image

Could you connect an appropriately sized heating element to the load output of an MPPT controller, and just set the low-voltage cutoff for load output to a high value, near full SOC?

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setkiki avatar image

Thank you for the information provided, these are very helpful to me.


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MihaiR avatar image

Hi,

This is what I have installed in front of my ESS system, between distributor grid energy meter and ESS Victron meter. Hence, any energy exported by ESS will heat the water in my hot water tank. Starting from March till October I didn't pay any money for producing hot water for my family

http://www.theecostore.co.uk/eco-store/apollo-gem-compact-wireless/


Regards,

Mihai

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valos avatar image

I’m using Rolls 605 flooded batteries FOR about 18 months, the boiler uses PV energy between April and October.

I haven’t seen any significant degradation in battery performance so far.

The PV array is 5 kw.

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lief ryan avatar image

what about using a second charge controller (running an inverter without a battery, connected to a water heater) turned on and off (via a relay) from the aux of the main charge controller (midnite classic) that way you could use ac for longer cable runs without cycling the batteries?

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Better to use a PV inverter instead, but I don't think this will be a reliable solution either. But it might work.