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====== Self-jumpstarting ======

Self-jumpstarting means jumpstarting one's own vehicle without the use of another vehicle.  It's done by [[electrical:12v:alternator|combining]] house and chassis batteries by one of several methods discussed below. 
 
Note:  regardless of specific method used, it will be gentlest on the system to **combine the batteries and wait a few minutes for the starter battery to come up** instead of immediately attempting to start. This will minimize((or eliminate, if the connection is broken prior to starting)) the amount of current flowing from house bank to vehicle chassis. This may be especially important with Li chemistries that have BMS protections. 

===== jumping from the house bank =====


This will be easiest if one already has some kind of [[electrical:12v:alternator#isolators|isolator/combiner]] setup. If not, one can run jumper cables from the house bank, or physically remove the house bank and carry it to the starter battery area. 
==== manual switches ====

Switches used as manual isolators will self-jumpstart when in the ON position. 
==== solenoids ====

Solenoids/relays //always// self-jumpstart assuming there is enough voltage in the starter battery to energize the solenoid.((If starter batt voltage is too low you can use a jumper wire to energize the solenoid from the battery bank. It's not passing charging current, just powering the electromagnet in the solenoid.)) It is a mechanical connection and power will flow both ways.

==== voltage sensing relays ====

Some VSRs have a provision to combine the batteries for self-jumpstarting.  

Examples:  

  * [[https://amzn.to/2Ri2jQV|Battery Doctor]] - integrated button
  * [[http://amzn.to/2h2tDxp|Sure Power 1314]] - user-added wiring(("Connect a #14 gauge wire from the start position of the ignition switch to the Start terminal of the Battery Separator. Make this connection at the ignition switch. This wire should only have voltage when the ignition switch is in the start position. Note: The start signal must be able to produce at least 3V* in order to provide automatic boost, see connection diagram above for manual operation option." - https://www.ase-supply.com/Sure_Power_1314_200_Battery_Separator_p/sp-1314-200.htm))
  * [[https://amzn.to/3h5iMUd|Victron CT]] - user-added wiring to "start assist" terminal
  * Precision Circuits [[http://precisioncircuitsinc.com/product/battery-isolation-manager-2/|BIM]] and [[https://amzn.to/3c6XwMv|Li-BIM]] - user added wiring to "sig" terminal((http://www.precisioncircuitsinc.com/wp-content/uploads/2017/06/00-10041-2xx-Battery-Isolation-Manager-Rev7-1.pdf)) - see [[https://www.explorist.life/how-to-wire-a-li-bim-battery-isolator/|this article]]
  * [[https://amzn.to/3CHoTt4|Blue Sea ML-ACR]] can combine banks manually or with the included remote switch


==== diode isolators ====

[[electrical:12v:alternator#isolators|Solid state isolators]] are diode based and will not allow power to flow from the house battery to the starter battery.  Therefore they cannot be used to self-jumpstart on their own (see [[electrical:12v:self-jumpstarting#adding_self-jumpstart_to_diode_isolators_and_dc-dc_chargers|below]], including the Ctek exception). 
==== DC-DC chargers ====

As with diode-based isolators, DC-DC chargers typically cannot pass power back from the battery bank to the vehicle; there are exceptions.  Read below for workarounds and different approaches. 



==== adding self-jumpstart to diode isolators and DC-DC chargers ====

It adds a layer of complexity, but a relay with a switch can be used to [[https://www.redarc.com.au/bcdc-dual-with-jump-start-feature-the-ultimate-battery-setup|bridge the batteries manually]].

Note the Smartpass does this when added to the CTEK D250-series chargers.


===== maintaining starter batteries =====

Some [[electrical:12v:b2b#examples_-_combo_with_solar_charge_controller|combo DC-DC chargers]] contain logic to maintain the starter battery when solar power is present.

Some standalone solar charge controllers like the [[https://amzn.to/2PPTD2L|Morningstar SunSaver Duo]] can, for example,  charge the start battery with 10% of solar harvest and the house battery with 90% using different charging profiles.  As with DC-DC above, it's not self-jumpstarting but can help prevent the dead starter battery. 

[[electrical:12v:alternator#voltage-sensing_relays|dVSR isolators]] (including [[electrical:12v:alternator#lithium-specific_vsr|the Li-BIM]]) automatically connect the banks when the voltage on either side reaches defined setpoints. 

Some Victron Multiplus models have a 4A starter battery maintenance feature. 


There are dedicated maintainers:

  * Some RVs were equipped with original Trik-L-Start or lithium-compatible Amp-L-Start modules by LSL Products, which is [[http://www.lslproducts.net/|apparently out of business]].
  * The [[https://amzn.to/47HMMyn|Xantrex echo charge]] maintains the chassis battery at up to 15A.


Experimental:  RV With Tito has [[https://www.youtube.com/watch?v=exQSsTiclOo|uses a PWM solar charge controller to maintain starter battery from the house bank]].  

Also see [[electrical:12v:alternator#gotchas|the subarticle on combiner gotchas]].

==== starter battery chargers alongside DC-DC chargers ====

If a DC-DC is present and relatively weak shore power charging is applied to the starter battery there are circumstances where the DC-DC can cycle on-off constantly.  Let's consider a 20A DC-DC and a 10A starter battery maintainer.

  - starter battery at 12.7v before charging applied
  - starter battery voltage rises from 10A charging
  - DC-DC sees >13.4v and [[electrical:12v:b2b#sizing|starts pulling ~22A]] to charge house battery at 20A
  - starter battery drops to 12.6v and DC-DC charger stops
   - repeat forever

To avoid this scenario either:

  * ensure the DC-DC rating is smaller than the starter battery rating; or
  * apply the shore power charging to the house bank side instead((for DC-DC models with starter battery maintenance, see above))


===== waking lithium batteries =====

Lithium banks can go dormant at low voltages in order to protect themselves:

  - the BMS turns off the DISCHARGE channel to keep cell voltage from going any lower
  - so the battery internally has ~11.0v or whatever but does not pass that voltage to the terminals on the outside of the battery case
  - which means smart chargers don't see battery voltage
  - and think there's a problem so they won't start(("too smart for their own good"))

What we need is a //dumb// voltage source to get the party restarted.  The starter battery will do nicely.  

  * Rigs with IGN-triggered relays can briefly turn the key to ACC then back off.((don't leave it on ACC long or the dead Li will suck power from the starter battery.  Either turn ACC off again or actually start the vehicle.))
  * Rigs with voltage-sensing relays will have to actually start the engine or press a manual override switch to activate the VSR and wake the lithium bank.
  * Rigs with diode- or FET-based isolators would start the engine to spin the alternator and get power flowing through the isolator to the sleeping lithium









===== jump packs =====
[[https://amzn.to/2ITeBba|Lithium "jump packs"]] have become more popular.  Lithium-chemistry batteries can discharge quickly, so even relative small packs can jumpstart a car. 

'Dwellers may want to pick a jump pack that has 12v or USB outlets so it can have other uses.
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