Mobile electricity, yet another DIY solution: LaBora

type: note | domain: technology | topic: backgrounders | lang: en | pub: 2020-08-12

Please do not take this information for granted yet. It is a study in order to prepare and learn and I am asking for input before the stage of building, starting May 2021. This page probably will contain serious flaws at this point. I really appreciate input, feel free to leave a comment.

General

• Usage: a mobile office (Fiat Ducato L4H2), to be installed 2021 - she is nicknamed "LaBora".
• "Intelligent alternators" spoil the show these days.
• LFP or LiFePO4 batteries are very interesting.
• Solar energy is an option.
• Add something to this world by try and error, asking, learning and publishing, i.e. this page.
  • Costs are limited and approach is basic, contrary to quite fancy and expensive solutions.
  • Goal: quality, safety and reliability within reasonable limits.
  • Input is truly more than welcome. However preoccupied opinions and dogma's like "Stuff from China always sucks" and "You get what you pay for" is not appreciated.

An approach, thoughts

About the LFP, LiFePO4 units

• With proper LFP offered very affordable at some spots (2020), it seems a logical choice.
• Unfortunately I've experienced a ruined brand new battery set because of a faulty BMS, draining over balance wires. That is why the battery can be isolated completely by using DIP switches and a main switch before P-, in case of longer term storing.
• Banks of 4s (series) are not interconnected. It is possible to monitor each individual cell this way and one faulty cell will not influence a healthy connected cell.
• It does not seem to be a problem to use multiple banks in parallel. However, connecting banks becomes dangerous when voltages between banks are not equal.
• BMS should only close B- and P- within proper voltage range. BMS has an important role and acts as a safety switch.
• Temperature alerts, high and low, should be dealt with.

About Solar energy...

There is a possibility to use 6 to even 12 units of 100 peak Watt, 18 V, on the roof.

• Minuses:
  • Somewhere around 100 kg on the roof.
  • More fuel usage.
  • It is not a camper, there is plenty of opportunity for charging by driving and or by means of an external supply. That counts for our situation, maybe not yours...

• Plusses
  • Using low weight flexible panels might be a solution if I am able to attach them in a rigid and responsible way. I am thinking about a roof curved thin aluminium sheet as substrate with ~1", 3cm, space between roof and sheet for ventilation, all on an aluminium frame.
  • Less worries about batteries drained in time.
  • Spare environment.

About "Intelligent Alternators"...

• The voltage is too low for direct loading, despite impressive current output.
  • Direct loading is never a good idea for LFP, no constant current (cc) and constant voltage (cv) stages.
  • Chip tuning and tricks like killing load temperature sensors is not preferred.
• I've asked Fiat about it, they delegated the question to a dealer, probably not going to get any useful information, but I'll give them a chance.
• So far, all established DC-DC converters that increase voltage seem to have a reasonable, perhaps bit spicy, price tag. Let's list them, they were hard to find...
  • But first, why not use a DC-AC inverter, combined with a proper battery charger? Since most energy will not come from the alternator but from external power supply, it seems a proper, easy, acceptable and affordable way in this scenario. On top of that, a charger is needed anyhow, so an extra inverter is the only investment with impact. Big downside is the loss, it is not quit efficient.
  • Then there are products like "Renogy DC-DC Battery Charger" 60 A, with a reasonable price.
  • "Victron DC/DC Chargers" Orion-Tr Smart" 360W (~30 A) and the expensive "Buck Boost".
  • Ctek has a annoying unstructured site with model "SMARTPASS 120S". Looks promising, reasonable price and I've got 13 years experience with a loader that does its job uninterrupted.
  • From Asian sources there is not much available it seems. 80 W "Imax B6" for example. Not an option.

About charging...

• In this scenario there are multiple chargers: a dedicated main charger and one embedded in the main inverter with a small capacity.
• The main charger is limited should have a proper cc, cv and trickle profile during charging. Cc and cv: First constant current and the next stage is constant voltage until designated as "Full".
• How many Amps can the alternator handle without too much heating up under constant load?

About usage...

• This is also a point of using your head during use of electrical equipment, boil exactly the amount of water you need for your thee, don't bake cakes during battery use, and so on.
• Heating is covered by a diesel heater for:
  • Showering and warm water
  • Interior heating, preferable by using the - relay isolated - native heater ventilator in combination with a separate PWM controller, water valves.
• Kitchen machines, like a water boiler, induction cooker, magnetron, coffee machine, use a lot of energy but are used only shortly. They surely will play a role in total consumption. Exception is the fridge, consuming less, but working day and night.
• Work stuff like laptops and monitors are considerable consumers too. Aggressive sleep mode when not in use is essential.
• Then there is a collection of often unnoticed users that do have influence, like diesel heater, pumps, losses in inverters and electronics.
• Time will tell if it is doable. Escapes are making trips for both fun and charging and of course increasing the output of the charger.

Questions

I've asked for help here: DIY Solar Power Forum.

• Does this text contain serious errors?
• Fusing each bank with a breaker on the minus side leaves questions, if one bank is 90 Ah and acceptable constant discharge is 100 A (peak 300 A), what is a proper fuse value?
• Is there a solution that deals with voltage difference between banks?
• Is there a smarter way to overcome limitations of "smart" or "intelligent" alternators?