Budget charge from alternator addition to solar

[Yuri]

Hi dear community! Thanks administration for creating this forum. Hopefully it will be helpful.

Currently my Ford Transit 2016 camper van conversion uses 350W solar only to charge 12V 200AH LiFePO4 battery bank.
We have no propane, so it's all electric conversion with some massive loads like induction cooktop.
It works pretty well, but would like to add ability to charge battery bank while driving.
I don't want to spend $200 or more if it can be avoided.
I have idea I'm trying to implement, and would like to share it. Maybe something I missed.

I attached diagram to explays the idea.

The intention is to use DC-DC step up voltage converter to step up from 14V car alternator to lets say 35V and connect converter output to solar controller input. So when I'm driving alternator/converter will be like virtual solar panel for controller.
Ideally:
converter should have ability to limit output amperage, and should work only if alternartor running.
I ordereed some $20 DC-DC 1800W converter (I think it's not a real wattage, but hopefully enough for my needs) from China: https://www.aliexpress.com/item/32849390499.html?spm=a2g0s.9042311.0.0.429e4c4drULxhA

It was expected it has under-voltage protection (it does)
output current limiter (advertised, but sadly, it does not work)
output voltage regulator and input fuses (60A).

As sign that alternator running I use Victron BM relay set to 13.9V (release to 12.8), also I'm thinking to set converter undervoltage regulator to maybe 13.2V, to disable charging when rpm too low to protect alternator.

To limit current currently I use Victron charge controller. I set 30A (default) max current and it does not draw more than 30A.

As for me Pros:
- single device control my battery charging - solar controller
- when I ran alternator I saw 420W charging at solar controller that seems not bad for less then $50.

Cons:
- Total charging amps limited by solar controller to max 30A, so in full sun I will have the same 30A when driving.
- Converter does not limit current, and after some driving 45A converter fuse was fried (I downgraded it from 60A for testing) as I didn't want to run it with 60A fuse as my Ford Transit 12V CCP point has 60A fuse that will be pain to replace. Going to try again and limit under-voltage protection to 13V, hopefully it will not fry fuse again.

I would be happy to hear your opinion.
Something I missed?
Any recommendations about good DC-DC step up module with current limiter?
Also, any suggestion about what to use to draw some electrical diagram? I currently use draw.io. Maybe something faster exists.
Thanks.

 

[Getyourbone]

One of these work?

Has user configurable current out put and is a boost converter....limited to 10 amp output though.
Link to manual...

https://www.yampe.com/images/pdf/2907.pdf

Has OCP...have to purchase and install continuous use relay seperately for protection function to work

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[Yuri]

Thanks for MPPT step up, pretty interesting device.

 

[PHoganDive]

You do not want to connect a non-solar panel power source to the solar input of an MPPT charger. The way they figure out the maximum power point is to briefly load the panel(s) with an increasing load to measure where the target point should be. This load sweep normally brings the panels down to near zero volts. If it tries that with a battery or power supply connected, it can overpower the loading device in the MPPT and smoke it = dead MPPT. If the MPPT has a separate DC input for a generator or similar input, that should work ok.

 

[Yuri]

You do not want to connect a non-solar panel power source to the solar input of an MPPT charger. The way they figure out the maximum power point is to briefly load the panel(s) with an increasing load to measure where the target point should be. This load sweep normally brings the panels down to near zero volts. If it tries that with a battery or power supply connected, it can overpower the loading device in the MPPT and smoke it = dead MPPT. If the MPPT has a separate DC input for a generator or similar input, that should work ok.

That may be the reason why fuse was blown in DC-DC converter. I noticed that Victron MPPT controller does not take more than 420W from converter, I hoped it's a maximum it can take.
Probably it might be safe to connect power source that allows short circuit output and limits max output current.
Wondering maybe I can just somehow limit short circuit current, like connect incandescent light bulb in serial with DC-DC controller output. Probably light bulb not the best idea, but I guess it should be better way.
Thanks for information.

 

[Getyourbone]

You do not want to connect a non-solar panel power source to the solar input of an MPPT charger. The way they figure out the maximum power point is to briefly load the panel(s) with an increasing load to measure where the target point should be. This load sweep normally brings the panels down to near zero volts. If it tries that with a battery or power supply connected, it can overpower the loading device in the MPPT and smoke it = dead MPPT. If the MPPT has a separate DC input for a generator or similar input, that should work ok.

That sounds like one size fits all answer...

The 7120a controller can be used for the intended recommendation.


Just saying...

 

[Will Prowse]

Well you are going from 12v to 12v, so might as well use a current limited DC-DC converter circuit with variable output. Set the output to absorption voltage and you are done (for lifepo4). Just ensure it has current limiting. If it doesn't, you will fry it. Looks like you have one (linked in original post). Just use it to directly charge the lifepo4. Set output voltage to absorption voltage of your battery bank.

But boosting and going through SCC is not a good idea in my opinion. Also need to ensure that diodes are used so solar panels do not backfeed car charging system.

 

[Will Prowse]

Power point tracking algorithm not smart to use with a boost converter circuit. Think of the constantly variable resistance that it is trying to manage.

You could just use a typical battery to battery charger. Like a sterling. Or renogys cheap version of it. Sterling battery to battery is much nicer, but 3x the cost. I would still go with a typical current limited converter circuit (like one you linked) and set output voltage to absorption of battery.

 

[Getyourbone]

This controller works.

It states right in the instructions, I used it that way to test my system, and there are videos on YouTube and posts on other forums showing it.

If it didnt work, I would not have included it and then continue to state as such.

 

[Getyourbone]

Completely agree with not needing mppt however there may be other features with this that you are not going to easily find on a simple converter?

 

[Getyourbone]

Just ran across this if you haven’t already seen it...

???

I may just give it a try if I get around to buying a Pwm.

 

[Allan]

Initially, add a simple dash rocker switch to choose whether you want the chassis (engine/alternator/starter battery) to feed the cabin (house battery) in parallel. That switch gets it's (+) feed from the ignition/on circuit, so it only has power when the engine is running. And it's as simple as having a (-) battery ground (through the chassis), and running heavy positive wire (e.g. 00 from a welding shop) from your starter battery, to one large terminal of the contactor (aka relay, solenoid, see ebay link below) under your hood, typically near the starter battery, and the other large terminal goes over heavy wire to your house batteries. One small terminal of the solenoid goes to chassis ground, the other goes to the output of your dash switch.

When you flip the switch and the engine is running, the solenoid closes, and the starter and house batteries are in parallel with your starter battery. RV's have a switch on the dash that work identical to my description.

Plus, because you have Lithium house batteries, as Will typed, ahead of your house batteries: "Well you are going from 12v to 12v, so might as well use a current limited DC-DC converter circuit with variable output. Set the output to absorption voltage and you are done (for lifepo4). Just ensure it has current limiting. If it doesn't, you will fry it. Looks like you have one (linked in original post). Just use it to directly charge the lifepo4. Set output voltage to absorption voltage of your battery bank. "
- What Will Wrote.

Solenoid: https://www.ebay.com/itm/Solenoid-Relay-Marine-Battery-Isolation-switch-300-Amp/322046679196

& Buy a larger output alternator. Looks like the stock is 150amps. That means it likely outputs ~50amps at idle, putting a measly 15-20amps into your house battery. There's a 230amp that would probably generator more like 90 amps at idle, putting a more respectable 40amps+ in at idle: https://www.oreillyauto.com/detail/.../r113623a/6054512/2016/ford/transit-250?pos=3

You want to check the warranty, where you get the alternator. I just picked OReilly's out of a hat, they tend to have some better components, it says 'limited lifetime', I assume 'lifetime' means as long as you own the vehicle: it means you can bring in the alternator should a component on it fail, and swap it out for another one. Call ahead to make sure they have stock!

Chewing used bubble-gum:
Both the MPPT and the alternator can charge the same bank simultaneously. Very nicely drawn circuit so you have great drafting skills, however, like everyone else who already replied, the solution is simpler. And I don't want to repeat what people said about not feeding the MPPT with something other than solar.

Completely agree with not needing mppt however there may be other features with this that you are not going to easily find on a simple converter?

This was also my thinking about it - with a standard converter or for that matter victrons brand new orion smart dc-dc chargers directly charging the house battery you don't get a live amperage feed displayed from the converter or dc-dc charger like you do in the victron connect app from the scc (without having a shunt based battery monitor) and you also don't have the option of setting up low temperature disconnect like on the victron mppt scc - I was hoping to be able to feed alternator power via a converter through the victron scc for those reasons so all settings and customizations regarding the secondary battery remained the same regardless of solar or alternator charging

 

[Yuri]

Well, I tried to connect DC-DC step up converter to victron mppt input and it warked fine for a week. Victron limited current to 30AMPs, and battery was always topped off. Unfortunately my Chineese DC-DC step up converter current limiter didn't work, so I had to use Victron as current limiter. After one week my cheap DC-DC booster finally died during our trip.
So, it looks like I have to get some good quality DC-DC charger to avoid surprises. I'm thinking to have my Victron MPPT for solar panels, and make DC-DC charge batteries while driving at the same time.

I see several options :
Victron orion tr smart 12/12 charger
KISAE DMT-1250 SMART BATTERY CHARGER
Renogy DCC50

I like Victron products and lean towards their new smart charger, but I heard it back ordered till spring.
About Renogy I'm not quite comfortable that they do not engineer their devices, but more just put their labels on some Chinese stuff, so not sure about reliability.
For me KISAE DMT-1250 looks pretty interesting, but I know nothing about brand and what drawbacks this device have. Would live to hear first hand experience.

 

[fat_old_sun]

current limiting DC-DC charger for LFP batteries.

 

[Southwestern]

Very interesting topic

Renogy DC-DC seems to have quality issues and 25 volt max input from panels
https://www.amazon.com/Renogy-DCC50S-12V-50A-Multi-Stage/dp/B07W84SS41?th=1

More info on the topic here: "Careful – Alternator Charging Lithium (or how to not blow up your alternator) https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/

 

[grizzzman]

current limiting DC-DC charger for LFP batteries.

I have that set up on my table as we speak. It is being powered by a cheap 40 amp power supply (To mimic solar panels for testing) It works.