Jump start with lithium house battery?

[WhitH]

Thanks all. I have a Renogy DCDC that does only connect when the alternator is on and my house battery is a 100ah LiFePO from Renogy as well.

[boywonder]

Originally Posted by 1der

A fun little chore is to reset a BMS which has shutoff due to discharge - which can be done with the lithium jumper pack, which is what you would have used to jump start the engine

...Unless your Bluetooth-enabled BMS allows resetting with the swipe of a finger.....

[posplayr]

Originally Posted by Twoxentrix

I'll second the NOCO, but would recommend something a little more powerful for a Diesel - may be faced with trying to 'jump' more than once. They also come in handy to repower Laptops & Cell phones.
Periodically NOCO offers them for a really good 'Sale' price.
https://www.amazon.com/dp/B08WZFPXFM...1zcF9kZXRhaWwy

This was on sale and I picked it up for $56 before tax. Its 2500A rating really spins my 6.8L V-10. They seem to be out of business but both it and its smaller 1000A brother 9$40 before tax) seem to turn it as I recall.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[posplayr]

Originally Posted by WhitH

Got it. If I were desperate enough to try this I’d just use alligator clip jumper cables. Would it be smart to disconnect the DCDC charger before connecting?

I had a plan to charge the start battery from the lithium by using a separate 120VAC to DC charger (powered by an invertor) for a small >5 amp charge current was doubling up the DC-DC input wires.

Alternatively, you could just wire a pair of heavy-duty switches from the DC-DC input (+) and (-) to the DC-DC Output (+) and (-) respectively. Before switching ON make sure the DC-DC is OFF.

I would not want to try and run a long jumper cable from the Haus battery to the start battery especially when you already have the wires available.

Of course, if you can find a good deal on a start booster they are very small and convenient albeit pricy.

I sketched a concept with a safety interlock. The DC-DC connections typically would have long wire lengths between the Alternator/Start Battery and the DC-DC which will inherently limit large currents being pushed by the house lithium. So the monetary might be held down for 1-2 minutes or even while starting.

[boywonder]

Originally Posted by posplayr

Alternatively, you could just wire a pair of heavy-duty switches from the DC-DC input (+) and (-) to the DC-DC Output (+) and (-) respectively. Before switching ON make sure the DC-DC is OFF.

This is essentially what I have.....

I'm using a large red Blue Sea battery battery combiner across a Victron Orion DC-DC converter.






When the batteries are combined, the Orion wakes up and gets quite hot...(they run really hot in normal operation) since I'm basically shorting the converter's input and output.

I just turn off the Orion using the bluetooth app..all good.

I leave everything in this state when parked in my driveway so that my house battery connected solar will also charge the starter battery when parked between trips.

In the event that I need to start the van off of the house battery I would just combine the batteries, turn of the DC-DC converter and wait 15-20 minutes before cranking the engine.

[posplayr]

Originally Posted by boywonder

This is essentially what I have.....

I'm using a large red Blue Sea battery battery combiner across a Victron Orion DC-DC converter.






When the batteries are combined, the Orion wakes up and gets quite hot...(they run really hot in normal operation) since I'm basically shorting the converter's input and output.

I just turn off the Orion using the bluetooth app..all good.

I really don't like the idea of shorting inputs to outputs with the DC-DC engaged, but if the Bluetooth is the only way to turn it off you don't have much option. Can't you disable it before shorting your terminals?

Originally Posted by boywonder

I leave everything in this state when parked in my driveway so that my house battery connected solar will also charge the starter battery when parked between trips.

In the event that I need to start the van off of the house battery I would just combine the batteries, turn of the DC-DC converter and wait 15-20 minutes before cranking the engine.

I have a 120VAC refrigerator so would need to have the inverter on making it also available for a small 5 amp charger for the start battery.

Ironically I plan to put 300 Amp-hr of AGM with my 200 amp-Hr LiFePO4 to guard against load dump events and add extra capacity. I could add another 280 of LifePO4 but will have to see how the new 12VDC A/C loads are.

I might need to rethink this, it is easier to just make the jumper connections .

I assume when you are boondocking you disconnect the House from the Start batteries as well as when you are driving with the DC-DC active?

[posplayr]

I finally found a reason to post this chart I spent last week producing.

I just bought a pair of each These batteries are about $100 apiece used as a backup for 5 years or 1/2 the estimated life. They are cycled one a year which is the only use they have seen. The data safe has a date code of 2019.

Data Safe 12HX505-FR (rated 119 A-h 8 Rate to 1.75 VPC (10.5V battery)

Dynasty UPS12-600MR (rated 148 A-h 20 hr Rate 1.75 VPC (10.5V battery)


I measured both as a pair and get :

Data Safe 12HX505-FR 150 A-hr (5.5hr @ 30 amps load to 11.95V)
https://pwrstoragesolutions.com/prod...ry-12hx505-fr/


Dynasty UPS12-600MR 167 A-hr (5.5 hr @ 30 amp load to 11.95V)
https://powerprosinc.com/UPS12-600MR-C-D-Dynasty.html

The plot shows the recorded voltage vs SOC for the two pairs of AGM's with a typical LiFEPO4 characteristic. The analysis is to estimate what happens with the LiFepo4/AGM parallel connection. I indicated the stable switching points.

I will probably use the Data Safe because they have a much lower internal resistance 2.3 mOhm vs the Dynasty which I measured about 8.6 mOhm. much.

. One pair will go in a fixed trailer in the mountains and the other in modified frame battery boxes for the 2000 XLT EB E-350.

[posplayr]

Looking at the Victron DC-DC, this is what the connections would look like with the Switch Wonderboy added. There is an external ON-OFF switch as well. If the DC-DC had a higher rating (e.g. 40+ amps ) then the switch would be used to avoid charging at idle.

[boywonder]

Originally Posted by posplayr

I really don't like the idea of shorting inputs to outputs with the DC-DC engaged, but if the Bluetooth is the only way to turn it off you don't have much option. Can't you disable it before shorting your terminals?

Yes.....I disable the DC-DC converter before combining the batteries. I didn't disable it the first time I combined them, that's how I discovered it gets quite hot.

Originally Posted by posplayr

I assume when you are boondocking you disconnect the House from the Start batteries as well as when you are driving with the DC-DC active?

Yes, exactly.

[boywonder]

Originally Posted by posplayr

Looking at the Victron DC-DC, this is what the connections would look like with the Switch Wonderboy added. There is an external ON-OFF switch as well. If the DC-DC had a higher rating (e.g. 40+ amps ) then the switch would be used to avoid charging at idle.

Exactly.....and yes you can disable the Orion with a physical switch, didn't do that but it would certainly work.