Hi,
I have a vw new California ocean van and want to connect my Mppt 75/15.
In the old van I had a single 140AH AGM battery. The new van is equipped with two 40AH LiPo batteries. Does anyone know where (not) to connect the battery+/- connectors of the Mppt?
Thanks!
Tobias
Hello,
First off, based on the sparse wording and brevity of your question, I suspect that you don’t have a background in electrical engineering. No worries, but my first recommendation would be, that if you are not comfortable working with voltages and currents that can spot weld tools to your new van, seek out the assistance of a professional or dedicated hobbyist. LiFePO4 batteries have an energy density that can literally start fires. If this is something you do want to do, then be aware that there is a learning curve here regarding electrical wiring assembly and installation.
First off, a few questions. What are the (2) 40Ah LiFePO4 batteries powering? What is the expected/desired usage of the batteries? Will there be cold temps involved (<0 degrees C/<32 degrees F)? Do the batteries have internal heaters? What brand are these batteries? Are they already set up to take a charge from any other source (diesel/gas engine, AC-to-DC charger, etc.)? Is the MPPT unit still programmed for AGM batteries? Can the MPPT unit be reprogrammed for LiFePO4 batteries? Based on your wording, it looks like it might be some variant of a Victron charge controller (75V max/15A max). What is your expected current output of the MPPT unit with your solar array? Will you be adding anything else to the system? It is better to plan ahead and make accommodations for future needs/wants.
In the most basic sense, if the MPPT unit can be programmed with a LiFePO4 charge profile, you will need to connect the MPPT unit’s battery (+) to the batteries’ positive terminals and the MPPT unit’s battery (-) to the batteries’ negative terminals, but there are more details to be aware of. Assuming you will be working with a typical 12V arrangement, you have two choices for parallel battery wiring:
OR
You mentioned nothing about the solar panels connected to the MPPT unit, but you should also have some kind of service disconnect between the panels and the MPPT unit. Depending on the size and configuration of your solar, you may need inline fusing too.
Notes:
–This reply is not meant to complete your education on installing LiFePO4 batteries. These things can be dangerous. If you still want to do things yourself, you are expected to DO YOUR OWN RESEARCH regarding wire and fuse sizing.
–Mount these batteries securely. They will cause a fire if you do not. When in doubt, over-engineer mounting and insulating.
–Mount all wiring securely. Wire ties are cheap. Vans aren’t.
–Don’t cheap out on wire. Over-estimate current usage. Don’t cut wires too short. An extra 6"-12" will not hurt anything if fastened down properly. Use a reputable brand.
–Don’t leave any bare copper or anything with an electrical potential exposed, Marine-grade heat-shrink tubing is your friend.
–Don’t cheap out on fuses holders and fuses. Use reputable brands.
–Don’t cheap out on the solar disconnect. Use a reputable brand.
–Fuses protect the wire, not the hardware.
–Have fun learning something new!
packrat
Hi,
Thank you very much for your kind and detailed reply, and also apologies for the brevity of my question, and likely nativity and clear lack of knowledge.
I had support by a dedicated hobbyist with regard to fusing/disconnecting the Mppt to the single Batterie (and 150W foldable solar Panel). The use case in the old and new camper is the same: power a small fridge, some lighting, and a diesel heater when needed. Of course appliances are slightly different, but all on a 12V network. The Mppt can (and has been) switched to manage LiPo batteries.
The new van is professionaly built by VW, including the electric Installation. Since it is a default configuration, I was hoping someone knew how the batteries are setup and thus how to connect the Mppt.
Thanks,
Tobias
Tobigas,
Depending on it’s age and remaining capacity, moving from your 140Ah AGM battery to the (2) 40Ah LiFePO4 batteries you’ve probably just reduced your overall storage capacity. At least in theory. Here’s what I’m thinking. Lead-acid batteries, even the AGM variants, do not like to be discharged much below 50% of their rated capacity before accelerated wear begins. So, when it was new, the AGM battery really only had about 70Ah of usable capacity. With no excessively deep discharges and normal aging, I expect you probably got around 3-5 years of use before it’s capacity started to taper off. Less if it was treated badly.
With LiFePO4 batteries, the generally agreed upon depth of discharge is around 20%, so you get a little more out of them. But now you’ve reduced your rated capacity to 80Ah (2x40Ah). 80% of an 80Ah battery is around 64Ah. Does this capacity meet your needs with all of the loads you have described? It might, depending on other factors. If not, you may be able to add another 40Ah battery, if it will fit in your chosen location. On the bright side, lithium batteries are smaller, lighter, will last several thousand cycles (as opposed to single-digit hundreds), can take and deliver a lot more current quickly.
How is the battery to be used? Occasional (weekend) use with full charging cycles in between? 24/7 daily use? With a folding solar panel, it sounds like it won’t be permanently mounted to the vehicle. Does your climate and/or geography allow for lots of direct sunlight? I don’t know exactly what your solar panel is rated at, but most Victron units need at least a +5v differential before they start charging, so lets say you have a nominally 24V 150W panel. That might get you somewhere in the neighborhood of 8-10A of charging current at 12V in direct sunlight. Will this be sufficient?
If you are able to, post a photo of the specific MPPT unit. Depending on the model, you may be able to view and control it’s status with a smartphone or tablet. Also, it is probably a good idea to see if it has the latest firmware installed. Also include the detailed ratings of your solar array.
Depending on your use patterns, it may be beneficial to keep the the battery bank charged with the van’s engine/alternator than to just use solar. The wiring for that kind of setup is not much more complicated than the MPPT arrangement, however there are more complications with the necessary DC-to-DC converter, wiring installation and fusing. When you say “the van was professionally built…including the electric installation”, does this mean a bone stock van or has the vehicle been prepped for camping or travel living?
I know, I always seem to have more questions than answers…
packrat