An alternator controller is by far the most effective approach to alternator-charging lithium batteries. I stock and install the Wakespeed WS500 and Mastervolt Alpha Pro and they bring alternator control to a whole new level. The WS500 is advanced with innovative features including CAN Bus integration with Victron & the REC-BMS among others. The Alpha Pro is more fit & forget. The end result is a powerful, efficient and reliable alternator charging system.

There’s a misconception you need an expensive Balmar or Mastervolt alternator – you don’t and I can fit them to all factory domestic alternators used by the big marinisers. For some Barrus, Beta & Isuzu engines I’ve developed custom kits based around an awesome 200 amp Bosch alternator, running a 6PK poly-v drive-belt setup. It’s the same alternator used by Mastervolt in their top-of-the-line £2500 14/200 system. This 200A alternator can replace a 3.5 Dometic Travel Power – particularly useful with lithiums since the high loads caused by a Travel Power + large domestic alternator can mean one becomes redundant.

Up until now narrowboat engine marinsers haven’t had a solution to lithium charging – as of late 2021 Beta Marine have added options fitting a Mastervolt 12V 130A setup to the Beta 43 & Beta 50, and a Mastervolt 12V 90A setup to the Beta 38.


Both controllers I install share features necessary for optimised lithium charging:

‘Small Engine Mode’. Sets a 20% alternator output (ie. alternator load) somewhere below tickover, and a higher engine speed for full output. There’s a smooth linear progression between these 2 points. This enables you to set a precise lower load at idle reducing further at the lower in-gear tickover speed.

For the high output alternator it works so well – fitting a large (12V 100+ amp) alternator to a typical narrowboat engine (Isuzu, Barrus, Beta Marine) creates high loads at in-gear tickover speeds – this causes poor engine running and belt problems. On the Beta 43 & 50 engines it increases the likelihood of serious crank pulley issues.

This tool makes it possible to fit a much bigger alternator to an engine or belt drive system than you would normally be able to use. The system is dialled down to work closer to the edge of belt or engine limitations and the larger alternator enables unstrained reliability and continuous high output.

Alternator temperature sensing. Enables alternator temperature to be set where output begins to back off and then a high temperature at where the alternator stops charging. It’s similar to how the ‘small engine’ feature works and allows you to get the very most out of the alternator but keep things safe and comfortable. A 50% rule is often bandied around about max continuous alternator output. With so many variables (engine speed, pulley ratios, ambient air temperature, alternator type etc.) it takes just one occasion with extreme ambient air temp to melt the alternator – the rule just doesn’t work. A well setup system with good pulley ratios and a decent alternator enables far in excess of this 50%. With temperature sensing output is dynamic and always optimised.

Max Percentage Alternator Output. Good quality Lead Acid & Lithium batteries have a recommended max charge rate. This function can derate max alternator output to suit, or set a max alternator load based on belt drive limitations.

Integration with a Lithium BMS. A premium lithium setup with standalone BMS such as a Victron VE.Bus BMS, REC-BMS or 123BMS can enable full automatic alternator control. This completely removes the risk of a load disconnect damaging the alternator. When using drop in batteries it’s possible for these controllers to be managed by a Victron BMV monitor, with absorption voltage dialled down to limit chances of a load disconnect.

Any queries/questions call Ed 07922 163072

Example of a standard alternator being modified for charging lithium.

During build of new 2021 mega yacht limousine tender they looked at ways to charge 2* Mastervolt MLI Ultra 12/5500 lithium banks from the twin Sole Hyundai engines. It was impossible to physically mount Mastervolt alternators to the standard engines. I convert the factory fitted 150 amp Denso alternators to work with the Alpha Pro’s and full Mastervolt setup.


Practically any alternator can be adapted and the factory alternator is often a better solution than a full Mastervolt or Balmar system.

Example of a large alternator installation only possible with a Alpha Pro.

Basic spec of this new narrowboat: 510AH Victron AGM battery bank. Victron 3000 Multiplus. Victron BMV712 monitor. High power demands: Wallas diesel oven, Webasto CH (no stove), small induction hob, coffee machine etc.. Engine is the latest Beta 38 Greenline with standard budget-chinese 100A alternator.

Customer finds the standard setup struggles to charge the large AGM battery bank. The factory 100A alternator (Chinese copy of a quality European Iskra) has a massive ~75mm aluminium pulley. Due to non standard shaft thread size unable to fit a freewheeling pulley. Beta offer to make a 60mm aluminium pulley but customer wants to get things right. I fit a 200 amp Bosch alternator with Mastervolt Alpha Pro & increase cable sizes to suit.

Normally, with the small Beta 38 you couldn’t install such a big alternator. The 6PK belt & freewheeling alternator pulley combination is close to belt limitations and will just about run a 200A alternator. Limiting factor is engine power. The large ~230mm crank pulley enables near full alternator output at the 800rpm tickover – which the engine just isn’t capable of running. This is the case with other popular engines too: Beta 43, Beta 50, Isuzu & Barrus. With the Alpha Pro it’s possible. Absorption voltage is set to 14.6V and ‘small engine mode’ is setup to reduce output at lower rpm: At 800rpm tickover programmed to achieve ~65 amps. In gear tickover drops engine speed slightly and output to ~55 amps. Slowly raising revs, output gradually increases to 240 amps (3+kw) at 1200rpm. We back the max alternator percentage output to 70% to suit the max charge rate of the Victron AGM’s.

Alternator temperature sensor is added and Alpha Pro programmed to keep temperatures ultra safe. With the freewheeling pulley customer notices everything is significantly smoother. Alternator performance is transformed.

Mastervolt Alpha Pro + 12V 175A conversion on Isuzu to charge Valence Lithiums.

My customer has installed a 390AH Valence battery system along with other kit (Victron 3000 Multiplus, Victron BMV 712 Smart, Solar etc) and has found the standard 80 amp alternator on the Isuzu Canaline 42 doesn’t work with Lithium. I install my custom 6PK poly-v crank pulley upgrade along with a high quality & powerful 175 amp Iskra alternator & freewheeling pulley.

A Mastervolt Alpha Pro is added and absorption voltage is set to the recommended 14.2V. It’s important to keep max absorption voltage conservative with most lithium’s to protect cells from over voltage. Often the BMS is built in and a disconnect due to cell over voltage can potentially damage the alternator. Small engine mode brings alternator current down to ~ 55amps @ 800rpm tickover dropping to ~35amps at in-gear tickover. Full power is dialled back to ~130amps at 1100rpm. Without small engine mode alternator load is just too high – Engine runs very badly almost stalling on tickover and won’t rev.

An alternator temp sensor is added – as alternator temperatures rise over a pre-set level, output is gradually backed off and never exceeds a very safe 90 degrees C. The setup is superb and takes full advantage of the large alternator without compromising reliability or engine performance/refinement. I add a control switch in series with the ignition switch so alternator can be shut down when required. This is an important feature particularly useful for drop-in type lithiums with no alternator BMS control. My customer is delighted with the new setup. The video clip below shows the Alpha Pro’s current control – There’s a slight lag with sound due to the Victron BMV Smart connection.


Mastervolt Alpha Pro fitted to Barrus Shire 40 to charge 200AH Relion lithium on new build.

Customer originally installed a Victron Orion 12/12-30 DC to DC converter. I fit a Alpha Pro to the factory 12V 150A Prestolite avi144 domestic alternator. Derated to suit the Relion drop-in 200AH battery. Temperature sensor to keep alternator temperatures modest. Customer delighted with the new simple efficient setup and ability to recharge so quickly.

Example of a Dometic Travel Power swapout for 200A Bosch alternator + Alpha Pro.

The boat had a failed  3.5 powerbox and expensive estimate for repair. I fit a 200A Bosch + Mastervolt Alpha Pro package as a replacement and my engineer customer believes it’s far superior to the old Travel Power.

Features alternator temp sensing and small engine mode make this such a great option. For Lithium it enables charging far in excess of the typical Victron Multiplus 3000/120 + 3.5 Travel Power system, and uses ‘small engine mode’ which the Travel Power setup doesn’t have.

Alongside I install the full CAN Bus Mastervolt kit with MasterShunt, MassCombi & Easyview display. And fit a new set of Leoch AGM Lead Carbon batteries with leads to perfectly balance. A great feature of the Alpha Pro is you dial the current back to suit max charge rate of the AGM batteries.