Can multiplus invert from starting batteries

DIY
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1

Greetings!

I have a 2025 Ford Transit with dual starting batteries from the factory. I need to install a wheelchair lift in it for my son, 120VAC outlets for misc lower power things during trips, and we were thinking about installing a 12V fan or AC in the future (could do 120VAC if needed) for camping. I don’t want to turn this into a full camper setup with house batteries and was thinking I could do it with the factory starting batteries with limitations; basically always connect shore power when any load is required. The inverter would only work when the engine is on based on my plan. Well, after I already purchased the multiplus 12V/800VA, i noticed this statement in the manual:

“This product is not suitable for direct connection to a vehicle’s electrical system. It should be connected to a dedicated DC system that includes a dedicated service or house battery, appropriate fusing, and the appropriate gauge of DC wiring.”

I guess I should read first but it was advertised as an inverter and charger so I figured why wouldn’t it work, right? In hindsight, I should have just ordered an inverter and planned to install a switch for 120VAC power with no extra 12VDC loads. Without 12VDC loads while the engine is off, the multiplus is overkill. At this point I can either try to sell this one for a loss and downgrade to an inverter or hope that this one works OK. Does anyone know what the drawbacks are of installing this based on my wiring? The DC voltage range is well within the alternator’s range so the specs on face value appear like it’ll inverter the DC just fine. Maybe using the charging circuit to charge the starting batteries at full amps while connected to the car may be an issue instead of just a trickle charge?

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2

Good evening,

Indeed, you are correct and so is Victron about not using it in a “car”, the way you set this up works just fine, one drawback is, do not use the inverter while driving, e.g. as the alternator is doing its thing and this small inverter cannot cope with an alternator power (specially the smart alternators) at all!

Just make a relay, engine on, inverter off, and video versa…

That’s all.

With the very best regards, Jeroen.

3

Ok, that’s unfortunate because half the point of it was to be able to use 120VAC while driving. Otherwise I can just get a 120VAC air conditioner or fan for camping and power it directly from shore power instead of passing through the multiplus. All the multiplus gets me (without inverting while driving) is maybe a very short time of 120VAC before the starting batteries drain and that’s not worth it. I don’t want to install a bunch of house batteries because this is mainly a passenger van with an occasional light camping use.

Maybe I missed the warnings but I wish Victron was more clear in their marketing and data sheets. Even after seeing that one warning in the manual, I haven’t seen anything else indicating that it wasn’t a good product for this application, especially the generous AC and DC input voltage ranges. If the issue is DC ripple then I don’t even know where to go from here because the VE.Direct doesn’t give a value on DC ripple limit and the Inverter Compact states its alarm is the exact same ripple as the multiplus (1.25Vrms). So I can sell the muiltiplus for another device that has the same limitation, on paper at least.

Thanks for the reply.

4

Hi,
maybe first chek the rules/ laws in your country and the “certificates” on the victron download page.
Maybe it is not allowed to use an Inverter on the Vehicles DC starting battery during driving to avoid problems with Electro Magnetic compatibility and car electronics.

(By the way, a lot of Motorhome/ Caravan AC - Air Conditions are not allowed to use while driving - read the manuals …)

In your wiring you have two parallel Starting batteries. The top battery (1) and the bottom battery (2).
Don’t connect + and - of the loads to one battery.
Current will always choose the path of least resistance. Most of the current will therefore travel through the top battery.
And only a small amount of current will travel through the bottom battery.

Connect loads Wheelchair lift and Multi “+” to top battery (1)
and the “-” to bottom battery (2).

Maybe it could be a solution to use a Cytrix Battery coupler, to use the two batteries, one as starter the other one as housing battery
(with Start Assist Button - Jumper cable function).

Detailed information:
https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

5

Good evening,

Ok, now we understand a bit better what you want to do, you want the inverter to be on while driving only, and only then, correct?

Well, I discussed this with a couple of my colleagues, and to eliminate the alternator behaviour we recommend to put a capacitor ALS70A105QW025 to the battery and the inverter, as close as possible to the inverters battery terminals with these 4mm2 or 6mm2 silvered “speaker” cables as those are very fast with currents, there is another one, a more powerful, ALS70A135QT025, pending your wallet.

These capacitors can easily handle 40A all day long, and when calculated for your use, about a 400-isch years, so, time of estimated use of your van against time of 24 hour use of this capacitor in your install (54 years), 1:8 correct?

In that way you can use this small inverter with your alternator (which is way to big without such capacitor, as all alternators are basically) and you will have almost no ripple, also your batteries will charge faster and will have a longer lifetime and while starting this capacitor will give a healthy punch to your starter motor as well, saving your batteries also during a start.

You might ask, these guys with their very loud woofer installs use indeed a 1F-3F alu film capacitor for more boom, yes, they do, but these are all made in China (yes, really all, good for once and a while boom music), DO NOT use these with inverters, they will catch fire very soon with continuous use, ok?

The capacitor brand, which I cannot write here, but as mentioned above, is the best with inverters, some of these are in the moon wagon, and still working, normal lifetime 50-odd+ years….they have a calculator online so you can see yourself your capacitor lifetime against your use (if you know how to fill in the data btw).

With the very best regards, Jeroen.

6

Yeah, those are good points. I won’t be running an exhaust fan or AC (besides the van AC) while the engine is running so I should be good there. I just need a few smaller loads such as a small TV, charging laptop, my son’s medical stuff, etc while driving. The van has a customer connection point for hooking up small and large loads so I should check to see how that’s configured. I believe that it’s a bus bar with integrated fuse that connects to both batteries so the resistance should be relatively equal between batteries. If the cables or bus bars are big enough and the connections are good, it shouldn’t really matter but it’s worth a check since the lift could surge up to 100 amps. I’m leaning towards keeping the batteries paralleled if I can just because the lift is going to be a huge load but I’ll read over coupler information as well. Thanks for the reply!

7

Sorry, I wasn’t clear enough. And yes, basically just have the inverter working when driving; otherwise I was just going to have the AC pass through the multiplus and charge the starting batteries (if needed). With some research on the capacitor, it seems like a great idea. Do you happen to know anything about precharging the capacitor? I noticed some talk about that but not sure how often, if at all besides initial installation that it would be required. Without it, there may be an inrush but maybe I’m just overthinking this as it will likely last a lifetime anyway.

Noted on the cheap caps. I don’t want a fire.

Is there any problems with charging the batteries while the engine is off with the normal higher amp charging circuit of the multiplus? If it stays to 14.4VDC then I would think that should be well within the vehicle electronic’s input range.

8

Good morning,

A 10 ohm 5W or a 10 ohm 10W is enough, as these capacitors hold a small charge, and full on a short time.

But, Victron sells such resistor with led indication as well.

Regards, Jeroen.

9

I would be interested to know the thought process behind this. The alternator is a seperate DC power source, why would a Multiplus need to “cope” with its power output?

Theres no such thing as one cable “being faster with currents” as another. Different materials have different resistance values, yes, but resistance is not equivalent to speed. Use any decent copper cable in the appropriate gauge and you’ll be fine. What is the appropriate gauge? Use the Victron Toolkit app or the Wiring Unlimited book also from Victron.

10

Good Morning,

@chrigu, we mount these silver coated cables on the capacitor(s) only.

These have more strands and so very flexible, are coated and so better corrosion resistance, and are “faster” delivering currents, specially with a ripple present, that’s the cables we always use and have used with utmost results.

An alternator creates quite some ripple (pending which type), and so it is not a pure DC voltage as you might think, easy home test, start your car, switch on all your lights, measure with a multimeter AC voltage on the battery, you will be very surprised with some alternators and with older batteries.

Regards, Jeroen.

11

DC ripple is not power. That DC ripple can be too high for an MP is a thing, yes. But an alternator can charge with 10W or 1kW of power, the MP is not affected by that power (im aware that higher power output also increases DC ripple, but again, its two things). Adding capacitance can help indeed.

Again not a thing. Silver coating indeed lowers the specific resistance of a cable, but it doesnt last since silver oxidizes fast which increases ots electrical resistance. You can get the same low resistance and flexibility by using a fine stranded copper cable.

Dont fall for snakeoil, the only benefit is in the pockets of the seller.

12

Good morning,

@chrigu read this, VDC ripple improvements - #103 by Jeroen2

Regards, Jeroen.

13

I know of this thread, but your missing my point.

If you want to warn people of potential issue with DC ripple then talk about DC ripple and not power