| Schedule of disaggregated net sales | 
    |  |  | Three months ended September 30,
 |  |  
    |  |  | 2019 (Unaudited) |  |  | 2018 (Unaudited) |  |  
    | DC power systems |  | $ | 6,713,525 |  |  | $ | 4,958,670 |  |  
    | Engineering & Tech Support Services |  |  | 63,011 |  |  |  | 39,445 |  |  
    | Accessories |  |  | 162,782 |  |  |  | 63,043 |  |  
    | Total net sales |  | $ | 6,939,318 |  |  | $ | 5,061,158 |  |    
    |  |  | Nine months ended September 30,
 |  |  
    |  |  | 2019 (Unaudited) |  |  | 2018 (Unaudited) |  |  
    | DC power systems |  | $ | 23,146,223 |  |  | $ | 15,288,835 |  |  
    | Engineering & Tech Support Services |  |  | 232,998 |  |  |  | 69,667 |  |  
    | Accessories |  |  | 543,430 |  |  |  | 390,343 |  |  
    | Total net sales |  | $ | 23,922,651 |  |  | $ | 15,748,845 |  |    
    |  |  | Three months ended September 30,
 |  |  
    |  |  | 2019 (Unaudited) |  |  | 2018 (Unaudited) |  |  
    | Telecom |  | $ | 6,753,226 |  |  | $ | 4,246,099 |  |  
    | Government/Military |  |  | 39,822 |  |  |  | 659,912 |  |  
    | Marine |  |  | — |  |  |  | 32,016 |  |  
    | Other (backup DC power to various industries) |  |  | 146,270 |  |  |  | 123,131 |  |  
    | Total net sales |  | $ | 6,939,318 |  |  | $ | 5,061,158 |  |    
    |  |  | Nine months ended September 30,
 |  |  
    |  |  | 2019 (Unaudited) |  |  | 2018 (Unaudited) |  |  
    | Telecom |  | $ | 22,497,099 |  |  | $ | 14,054,886 |  |  
    | Government/Military |  |  | 588,482 |  |  |  | 1,257,292 |  |  
    | Marine |  |  | 60,642 |  |  |  | 87,010 |  |  
    | Other (backup DC power to various industries) |  |  | 776,428 |  |  |  | 349,657 |  |  
    | Total net sales |  | $ | 23,922,651 |  |  | $ | 15,748,845 |  |  | 
| Schedule of components of inventory | 
    |  |  | September 30,  2019 (Unaudited) |  |  | December 31, 2018 |  |  
    |  |  |  |  |  |  |  |  
    | Raw materials |  | $ | 9,654,350 |  |  | $ | 6,060,448 |  |  
    | Finished goods |  |  | 4,818,545 |  |  |  | 2,741,321 |  |  
    |  |  |  | 14,472,895 |  |  |  | 8,801,769 |  |  
    | Less: Inventory reserve |  |  | (330,000 | ) |  |  | (330,000 | ) |  
    | Total Inventories, net |  | $ | 14,802,895 |  |  | $ | 8,471,769 |  |  | 
| Schedule of reconciliation of the product warranty liability | 
    | Changes in estimates for warranties |  | September 30, 2019 (Unaudited) |  |  | December 31, 2018 |  |  
    | Balance at beginning of the period |  | $ | 175,000 |  |  | $ | 175,000 |  |  
    | Payments |  |  | (381,301 | ) |  |  | (364,163 | ) |  
    | Provision for warranties |  |  | 381,301 |  |  |  | 364,163 |  |  
    | Balance at end of the period |  | $ | 175,000 |  |  | $ | 175,000 |  |  |