Dynamically reconfiguring pack voltage for RV

skykooler

100 µW
Joined
Oct 6, 2010
Messages
7
I have a mobile home (a schoolbus conversion) which is designed to run off-grid and handle large power draws for a metalworking shop in the back. It's got 150 kWh of LiFePO4 batteries for this purpose, so it seems like a good candidate for an EV conversion. However, the pack voltage is 50v (set up as 16s10p). Obviously this is a rather low voltage for a traction motor that could move the bus, but that's what all the internal electronics are set up to run on. Is there any way that such a pack could be set up to switch between 16s10p and 80s2p so that I could use it as either a traction battery or an accessory battery?
 
Unless your needs for actual trip distances are bizarrely minimal, an electric skoolie will just not be a practical project. Maybe a millionaire seeking a Green virtue signalling PR stunt

And even if you wanted to spend 30K+ to just go a few miles per day

that tiny bank and its House circuits should be kept at its completely different voltage

and isolated from the EV side, except for a DCDC Charger.
 
Not practical how? I estimate that with that pack it should be capable of a good 40-50 miles per charge.

I know they need to be at a different voltage, I'm just curious as to whether it's feasible to tap that voltage off of the same battery in segments instead.
 
Switching 5 banks of 16s2p between series and parallel is going to be expensive whether you do it with contactors or manual connectors. I think you would need ~20 HV high current contactors or HV connectors on each subpack that can be plugged into either the series or parallel junction box based on which mode you need at that moment. You would need individual BMS's for each subpack. I don't think it's worth it.

What are your power needs for the home/metalworking configuration? Perhaps a high power isolated DCDC converter could supply your 50V needs from a permanently configured 200V traction pack. Isolated 12V DCDCs for electric vehicles are pretty common and not too expensive - 4 in series would get you 50V. I linked an example below.
https://www.alibaba.com/product-det...032.html?spm=a2700.details.0.0.3490678b7cB6C4

This wouldn't be as efficient as a 200V->50V DCDC, but I'm not sure about the available options for those.

Maybe you could also use a 50V output ACDC power supply and just put DC into it.

Note that 200V is a very lethal voltage and needs to be properly designed, built, and maintained. The pack should be fully isolated with regular, automatic isolation resistance measurements capable of shutting the system down. Properly rated cable and connectors should be used, preferably with HVIL. Please be safe.

Edit: Also wanted to add that 150kWh should give you ~100 miles of range at 60mph, more if you go slower.
 
The largest power draw I have is a 10 kW induction forge. There are a few 48V inverters which will supply that which is one of the reasons I'm going with 50V. There are additionally a 6kW inverter and a 1kW inverter for running the home circuits.

I hadn't thought of putting 12V converters in series. I'd definitely need larger converters than that though but that may be an option.

I estimated 50 miles based on the vehicle's current consumption of ~10mpg and extrapolating from the numbers I found for a Chevy Volt - is there a better way to estimate range?
 
skykooler said:
I estimate that with that pack it should be capable of a good 40-50 miles per charge.
I'm guessing under ten.

> I know they need to be at a different voltage, I'm just curious as to whether it's feasible to tap that voltage off of the same battery in segments instead.

No, you must draw from all segments evenly if you don't want to reduce lifespan by a lot.

Keep a separate 12V or 24V House bank. One of its charge sources can be a buck DC-DC converter, ampacity sized appropriate for its Ah capacity so it delivers say 0.4C maximum.

Less is cheaper of course. Vicor comes up on eBay sometimes pennies on the dollar.

Some people reco cheap Chinese stuff, if you go that way buy 5x the amps you want, plus carry spares.

 
skykooler said:
The largest power draw I have is a 10 kW induction forge. There are a few 48V inverters which will supply that which is one of the reasons I'm going with 50V. There are additionally a 6kW inverter and a 1kW inverter for running the home circuits.

I hadn't thought of putting 12V converters in series. I'd definitely need larger converters than that though but that may be an option.

I estimated 50 miles based on the vehicle's current consumption of ~10mpg and extrapolating from the numbers I found for a Chevy Volt - is there a better way to estimate range?

So your forge and home circuits actually run off 110V or 220V? In that case, how about a 200VDC->110VAC inverter. A 48V inverter is just going to boost that up to 160VDC before converting it to AC, so you just need one with a buck input stage.

For range estimation, there are electric type D school buses out there. Lion is one manufacturer. They advertise 100mi range for their 126kWh model.
 
How in the world did you fit 150 KW hours in an RV.

I put 26 Kwhours in one, for a solar installation, and that took up a lot of volume.

Anyway I'd probably do the 80s bank and just use a good DC converter from a junkyard electric car for the low voltage power.
 
Skoolies have a high carrying capacity

not that they can't get dangerously overloaded, imbalanced.

Of course actual range is reduced with every extra kg carried
 
Back
Top