Do NOT use Lithium House batteries for “BOOST” or cranking a Diesel???

[Jim McGarvie]

I guess since the website for our new PowerUrus lithium batteries says "Our batteries cannot be used as starting batteries for cars", I should probably avoid using the battery booster switch....

[Rocketman3]

Battery boost problem goes to the type of bms you have in the batteries multiplied by the number of batteries. 

if you use the boost to “recharge” the starting battery for 10min or so - no problem. However if you want to hit the starter - you need to know your overall capacities.

My diesel engine wants something like 900 to 1000 CCA (cold cranking amps) for the battery.
 

If your lithium bms can only deliver 100amps by spec, and you don’t want to take it to 100% - so let’s derate it 20% - now have 80amps available- multiply by say six batteries- that only gives 480amps for starting.  That may be enough for the generator- but not for the main engine. 
 

Now if your bms is rated at 200 amps - 20% derate would be 160amps - times four batteries is 640amps. Still a bit low. But maybe with the starting battery and a warmer engine- you might be ok or you could blow the FETs in the bms. 
 

One of the issues is the Locked Rotor Amps needed to start the starter turning - takes a lot of energy for that initial hit of power

That is why the manufacturers say you can’t use them as a starter battery. With enough batteries you could… but…

[Jim McGarvie]

1 hour ago, Rocketman3 said:

Battery boost problem goes to the type of bms you have in the batteries multiplied by the number of batteries. 

if you use the boost to “recharge” the starting battery for 10min or so - no problem. However if you want to hit the starter - you need to know your overall capacities.

My diesel engine wants something like 900 to 1000 CCA (cold cranking amps) for the battery.
 

If your lithium bms can only deliver 100amps by spec, and you don’t want to take it to 100% - so let’s derate it 20% - now have 80amps available- multiply by say six batteries- that only gives 480amps for starting.  That may be enough for the generator- but not for the main engine. 
 

Now if your bms is rated at 200 amps - 20% derate would be 160amps - times four batteries is 640amps. Still a bit low. But maybe with the starting battery and a warmer engine- you might be ok or you could blow the FETs in the bms. 
 

One of the issues is the Locked Rotor Amps needed to start the starter turning - takes a lot of energy for that initial hit of power

That is why the manufacturers say you can’t use them as a starter battery. With enough batteries you could… but…

Thanks Michael. I think I will avoid using the boost.

[Tom Cherry]

36 minutes ago, Jim McGarvie said:

Thanks Michael. I think I will avoid using the boost.

Yes…INDEED.  This information is good to know……..  I was not aware of that.  The info Mike posted seems logical and folks that are running Lithiums SHOULD be aware of this.  The topic title was edited for perhaps “more attention” as this is very important.  Too many times the “hype and advertising” glosses over certain issues and only promotes the features that folks “grab”.  Along theses lines, the AGM advantages are extolled but, the fundamental fact that one must exercise AGM’s, just like flooded is often “not emphasized”.  Thus we have members that pay a premium and don’t get any increase in life…often times, a decrease from the buggy whip “flooded”.

I would comment that a “warmer” diesel doesn’t mean one just shut off and still very HOT…. The “simple” load test is to turn off a diesel, on a really hot (90+) day.  Wait about 5 - 10 minutes….then, restart.  If you get that dreaded “OMG it ain’t gonna start” silence….and then it fires up….odds are you might think about new starting batteries.  When the engine has not really dissipated heat on a hot day, everything has expanded and you need all the amps you can get.

The comments about using the boost for a surface charge are inline with the owner’s manual.  BTW, the ISL’s have been known to need upwards of 1400 A.  Mine cranks a lot better since I replaced the 750 CCA’s with the 950’s that came as stock OEM on  the Dynasty ISL.

Here is a topic about an option.  I bought one and others have commented that it works.

 

[StellaTariche]

I did some research into replacing the starting batteries with a couple of “super capacitor” banks. Each bank looks like a 6-pack of tall boy beer cans (or spray paint cans)

Pro:

• They last 20 years
• They require no maintenance
• They deliver an insane amount of starting current.  You’ll end up leaving the undersized wire to your starter in place to limit the current (home made fusible link)
• They work in very cold conditions
• You can place them under your bed with all your house lithium batteries
• They don’t weigh much.
• They can be hooked up in parallel with your lithium house bank which simplifies converter charging off solar, pedestal and genset 

Con:

• Expensive. Not insanely so, but still more.
• Our typical rig requires two - and they don’t combine the typical way two batteries do (because they are capacitors and have almost no internal resistance, so they sometimes combine electrically like capacitors and sometimes combine like batteries). Easy to hookup, but calculating your CCA (cold cranking amps) is different than lead acid batteries in parallel.  The manufacturer will help you.
• Alternator charging (as always) is the problem. When you ditch the lead acid bank, you will lose the “buffering” and “regulation” of the choppy signal coming out of your alternator.  So the charging circuit off the alternator must be modified to prevent unintended reverse voltage / current dumps (back EMF) and you might have to “smooth” the the alternator signal yourself.
• They can only crank the engine 4 or 5 times (for about 20-25 seconds of cranking) before the super capacitor must “recharge”.  Recharge means letting them sit in parallel with your big lithium house bank for about 15 minutes before trying again.
• Their ‘self discharge’ rate is higher than both lead acid and lithium batteries.  You’ll want to keep your rig plugged in or on solar if storing for a long time (months). You could wire in a disconnect, but the you’d have to wait 15 minutes for them to recharge off your lithium house bank before starting.

Interesting concept though if you want to rid yourself of lead acid batteries and go all Lithium. 

Edited June 14, 2023 by StellaTariche

[dl_racing427]

1 hour ago, StellaTariche said:

I did some research into replacing the starting batteries with a couple of “super capacitor” banks. Each bank looks like a 6-pack of tall boy beer cans (or spray paint cans)

Pro:

• They last 20 years
• They require no maintenance
• They deliver an insane amount of starting current.  You’ll end up leaving the undersized wire to your starter in place to limit the current (home made fusible link)
• They work in very cold conditions
• You can place them under your bed with all your house lithium batteries
• They don’t weigh much.
• They can be hooked up in parallel with your lithium house bank which simplifies converter charging off solar, pedestal and genset 

Con:

• Expensive. Not insanely so, but still more.
• Our typical rig requires two - and they don’t combine the typical way two batteries do (because they are capacitors and have almost no internal resistance, so they sometimes combine electrically like capacitors and sometimes combine like batteries). Easy to hookup, but calculating your CCA (cold cranking amps) is different than lead acid batteries in parallel.  The manufacturer will help you.
• Alternator charging (as always) is the problem. When you ditch the lead acid bank, you will lose the “buffering” and “regulation” of the choppy signal coming out of your alternator.  So the charging circuit off the alternator must be modified to prevent unintended reverse voltage / current dumps (back EMF) and you might have to “smooth” the the alternator signal yourself.
• They can only crank the engine 4 or 5 times (for about 20-25 seconds of cranking) before the super capacitor must “recharge”.  Recharge means letting them sit in parallel with your big lithium house bank for about 15 minutes before trying again.
• Their ‘self discharge’ rate is higher than both lead acid and lithium batteries.  You’ll want to keep your rig plugged in or on solar if storing for a long time (months). You could wire in a disconnect, but the you’d have to wait 15 minutes for them to recharge off your lithium house bank before starting.

Interesting concept though if you want to rid yourself of lead acid batteries and go all Lithium. 

You have to be careful with ultracapacitors.  They can accept as much charge current as they can deliver.
Connecting a large capacitor bank directly to a large battery bank could easily destroy a battery switch, or even cause a dangerous arc flash. It's also not good for the capacitors or batteries.
You need a way to limit the charge current to protect your batteries and alternator from overload.

 

[StellaTariche]

Yup. Exactly. 

I originally thought they were a great way to replace a starting battery, but (as my lab guys, who actually know what they are doing have said) “nope. Not for the casual RVuser”

[6Wheels]

When on standby, a resistive element can be made part of the circuit to limit current.  During a starting event, a relay could be used to remove the resistive element and put the caps "on line" to start the engine.  Now for the math!  And boy what a relay.

 

We have put the Discovery up for sale and have already had a valid offer.  And, no, it is not a tag rig.  The listing went up while I was out of town. She didn't know the difference! 🙃

https://www.rvtrader.com/listing/2013-Fleetwood-DISCOVERY+40G-5026631705

I think I'll still hang around here for a while just to see how the group is doing.

[Ivylog]

If you don’t know how many amps your BMSs are, I would use the boost for several minutes to top off the engine batteries but disconnect before actually starting.
The size (amps and cost) of the BMS is often overlooked… the cheaper the battery the smaller (cheaper) the BMS. In building my own Lithiums I went with larger BMS and my combined amps is 1000… will use the boost when starting.